Planet Python

Last update: January 24, 2020 01:48 PM UTC

January 24, 2020

Abhijeet Pal

Python Program To Reverse a Sentence

Problem Definition Create a python program to reverse a sentence. Algorithm Take a string as input. Convert the sentence into a list of words. Join the list in the reverse order which ultimately is the reversed sentence. Program sentence = "dread it run from it destiny still arrives" word_list = sentence.split() reversed_list = word_list[:: -1] reversed_sentence = " ".join(reversed_list) print(reversed_sentence) Output arrives still destiny it from run it dread This program can be further be compressed. sentence = "dread it run from it destiny still arrives" print(" ".join(sentence.split()[::-1])) Output arrives still destiny it from run it dread Python lists can be reversed using the reversed() method, which can be used in place of list[ : : -1] in the program as follows. sentence = "dread it run from it destiny still arrives" word_list = sentence.split() reversed_list = reversed(word_list) reversed_sentence = " ".join(reversed_list) print(reversed_sentence) Program for user-provided input sentence = input("Enter a sentence :") print(" ".join(reversed(sentence.split()))) Output Enter a sentence :This is an input input an is This

The post Python Program To Reverse a Sentence appeared first on Django Central.

January 24, 2020 01:24 PM UTC

Stack Abuse

Using SQLAlchemy with Flask and PostgreSQL

Introduction

Databases are a crucial part of modern applications since they store the data used to power them. Generally, we use the Structured Query Language (SQL) to perform queries on the database and manipulate the data inside of it. Though initially done via dedicated SQL tools, we've quickly moved to using SQL from within applications to perform queries.

Naturally, as time passed, Object Relational Mappers (ORMs) came to be - which enable us to safely, easily and conveniently connect to our database programmatically without needing to actually run queries to manipulate the data.

One such ORM is SQLAlchemy. In this post, we will delve deeper into ORMs and specifically SQLAlchemy, then use it to build a database-driven web application using the Flask framework.

What is an ORM and why use it?

Object-relational mapping, as the name suggests, maps objects to relational entities. In object-oriented programming languages, objects aren't that different from relational entities - they have certain fields/attributes that can be mapped interchangeably.

That being said, as it's fairly easy to map an object to a database, the reverse is also very simple. This eases the process of developing software and reduces the chances of making manual mistakes when writing plain SQL code.

Another advantage of using ORMs is that they help us write code that adheres to the DRY (Don't Repeat Yourself) principles by allowing us to use our models to manipulate data instead of writing SQL code every time we need to access the database.

ORMs abstract databases from our application, enabling us to use multiple or switch databases with ease. Say, if we used SQL in our application to connect to a MySQL database, we would need to modify our code if we were to switch to an MSSQL database since they differ in syntax.

If our SQL was integrated at multiple points in our application, this will prove to be quite the hassle. Through an ORM, the changes we would need to make would be limited to just changing a couple of configuration parameters.

Even though ORMs make our life easier by abstracting the database operations, we need to be careful to not forget what is happening under the hood as this will also guide how we use ORMs. We also need to be familiar with ORMs and learn them in order to use them more efficiently and this introduces a bit of a learning curve.

SQLAlchemy ORM

SQLAlchemy is an ORM written in Python to give developers the power and flexibility of SQL, without the hassle of really using it.

SQLAlchemy wraps around the Python Database API (Python DBAPI) which ships with Python and was created to facilitate the interaction between Python modules and databases.

The DBAPI was created to establish consistency and portability when it came to database management though we will not need to interact with it directly as SQLAlchemy will be our point of contact.

It is also important to note that the SQLAlchemy ORM is built on top of SQLAlchemy Core - which handles the DBAPI integration and implements SQL. In other words, SQLAlchemy Core provides the means to generate SQL queries.

While SQLAlchemy ORM makes our applications database-agnostic, it is important to note that specific databases will require specific drivers to connect to them. One good example is Pyscopg which is a PostgreSQL implementation of the DBAPI which when used in conjunction with SQLAlchemy allows us to interact with Postgres databases.

For MySQL databases, the PyMySQL library offers the DBAPI implementation require to interact with them.

SQLAlchemy can also be used with Oracle and the Microsoft SQL Server. Some big names in the industry that rely on SQLAlchemy include Reddit, Yelp, DropBox and Survey Monkey.

Having introduced the ORM, let us build a simple Flask API that interacts with a Postgres database.

Flask with SQLAlchemy

Flask is a lightweight micro-framework that is used to build minimal web applications and through third-party libraries, we can tap into its flexibility to build robust and feature-rich web applications.

In our case, we will build a simple RESTful API and use the Flask-SQLAlchemy extension to connect our API to a Postgres database.

Prerequisites

We will use PostgreSQL (also known as Postgres) to store our data that will be handled and manipulated by our API.

To interact with our Postgres database, we can use the command line or clients that come equipped with graphical user interfaces making them easier to use and much faster to navigate.

For Mac OS, I recommend using Postico which is quite simple and intuitive and provides a clean user interface.

PgAdmin is another excellent client that supports all major operating systems and even provides a Dockerized version.

We will use these clients to create the database and also view the data during the development and execution of our application.

With the installations out of the way, let us create our environment and install the dependencies we will need for our application:

$ virtualenv --python=python3 env --no-site-packages
$ source env/bin/activate
$ pip install psycopg2-binary
$ pip install flask-sqlalchemy
$ pip install Flask-Migrate

The above commands will create and activate a virtualenv, install the Psycopg2 driver, install flask-sqlalchemy, and install Flask-Migrate to handle database migrations.

Flask-Migrate uses Alembic, which is a light database migration tool that helps us interact with our database in a much clearer way by helping us create and recreate databases, move data into and across databases, and identify the state of our database.

In our case, we will not have to recreate the database or tables every time our application starts and will do that automatically for us in case neither exists.

Implementation

We will build a simple API to handle and manipulate information about cars. The data will be stored in a PostgreSQL database and through the API we will perform CRUD operations.

First, we have to create the cars_api database using our PostgreSQL client of choice:

With the database in place, let's connect to it. We'll start by bootstrapping our Flask API in the apps.py file:

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello():
    return {"hello": "world"}

if __name__ == '__main__':
    app.run(debug=True)

We start by creating a Flask application and a single endpoint that returns a JSON object.

For our demo, we will be using Flask-SQLAlchemy which is an extension specifically meant to add SQLAlchemy functionality to Flask applications.

Let us now integrate Flask-SQLAlchemy and Flask-Migrate into our app.py and create a model that will define the data about our cars that we will store:

# Previous imports remain...
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = "postgresql://postgres:postgres@localhost:5432/cars_api"
db = SQLAlchemy(app)
migrate = Migrate(app, db)

class CarsModel(db.Model):
    __tablename__ = 'cars'

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String())
    model = db.Column(db.String())
    doors = db.Column(db.Integer())

    def __init__(self, name, model, doors):
        self.name = name
        self.model = model
        self.doors = doors

    def __repr__(self):
        return f"<Car {self.name}>"

After importing flask_sqlalchemy, we start by adding the database URI to our application's config. This URI contains our credentials, the server address, and the database that we will use for our application.

We then create a Flask-SQLAlchemy instance called db and used for all our database interactions. The Flask-Migrate instance, called migrate, is created after that and will be used to handle the migrations for our project.

The CarsModel is the model class that will be used to define and manipulate our data. The attributes of the class represent the fields we want to store in the database.

We define the name of the table by using the __tablename__ alongside the columns containing our data.

Flask ships with a command line interface and dedicated commands. For instance, to start our application, we use the command flask run. To tap into this script, we just need to define an environment variable that specifies the script that hosts our Flask application:

$ export FLASK_APP=app.py
$ flask run
 * Serving Flask app "app.py" (lazy loading)
 * Environment: development
 * Debug mode: on
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 172-503-577

With our model in place, and Flask-Migrate integrated, let's use it to create the cars table in our database:

$ flask db init
$ flask db migrate
$ flask db upgrade

We start by initializing the database and enabling migrations. The generated migrations are just scripts that define the operations to be undertaken on our database. Since this is the first time, the script will just generate the cars table with columns as specified in our model.

The flask db upgrade command executes the migration and creates our table:

In case we add, delete, or change any columns, we can always execute the migrate and upgrade commands to reflect these changes in our database too.

Creating and Reading Entities

With the database in place and connected to our app, all that's left is to implement the CRUD operations. Let's start off with creating a car, as well as retrieving all currently existing ones:

# Imports and CarsModel truncated

@app.route('/cars', methods=['POST', 'GET'])
def handle_cars():
    if request.method == 'POST':
        if request.is_json:
            data = request.get_json()
            new_car = CarsModel(name=data['name'], model=data['model'], doors=data['doors'])
            db.session.add(new_car)
            db.session.commit()
            return {"message": f"car {new_car.name} has been created successfully."}
        else:
            return {"error": "The request payload is not in JSON format"}

    elif request.method == 'GET':
        cars = CarsModel.query.all()
        results = [
            {
                "name": car.name,
                "model": car.model,
                "doors": car.doors
            } for car in cars]

        return {"count": len(results), "cars": results}

We begin by defining a /cars route which accepts both GET and POST requests. The GET request will return a list of all cars stored in our database while the POST method will receive a car's data in JSON format and populate our database with the information provided.

To create a new car, we use the CarsModel class and provide the information required to fill in the columns for our cars table. After creating a CarsModel object, we create a database session and add our car to it.

To save our car to the database, we commit the session through db.session.commit() which closes the DB transaction and saves our car.

Let's try adding a car using a tool like Postman:

The response message notifies us that our car has been created and saved in the database:

You can see that there is now a record of the car in our database.

With the cars saved in our database, the GET request will help us fetch all the records. We query all the cars stored in our database by using the CarsModel.query.all() function, which is provided by Flask-SQLAlchemy.

This returns a list of CarsModel objects, which we then format and add to a list using a list comprehension and pass it to the response alongside the number of cars in our database. When we request for the list of cars through the API in Postman:

The GET method on the /cars endpoint returns the list of cars as they appear in our database, as well as the total count.

Note: Notice how there's not a single SQL query present in the code. SQLAlchemy takes care of that for us.

Updating and Deleting Entities

So far, we can create a single car and get a list of all cars stored in the database. To complete the set of CRUD operations on cars in our API, we need to add functionality to return the details, modify, and delete a single car.

The HTTP methods/verbs that we will use to achieve this will be GET, PUT, and DELETE, which will be brought together in a single method called handle_car():

# Imports, Car Model, handle_cars() method all truncated

@app.route('/cars/<car_id>', methods=['GET', 'PUT', 'DELETE'])
def handle_car(car_id):
    car = CarsModel.query.get_or_404(car_id)

    if request.method == 'GET':
        response = {
            "name": car.name,
            "model": car.model,
            "doors": car.doors
        }
        return {"message": "success", "car": response}

    elif request.method == 'PUT':
        data = request.get_json()
        car.name = data['name']
        car.model = data['model']
        car.doors = data['doors']
        db.session.add(car)
        db.session.commit()
        return {"message": f"car {car.name} successfully updated"}

    elif request.method == 'DELETE':
        db.session.delete(car)
        db.session.commit()
        return {"message": f"Car {car.name} successfully deleted."}

Our method handle_car() receives the car_id from the URL and gets the car object as it is stored in our database. If the request method is GET, the car details will be simply returned:

To update the details of our car, we use the PUT method and not PATCH. Both methods can be used to update the details, however, the PUT method accepts an updated version of our resource and replaces the one that we have stored in the database.

The PATCH method simply modifies the one we have in our database without replacing it. Therefore, to update a CarsModel record in our database, we have to supply all the attributes of our car including the ones to be updated.

We use the details to modify our car object and commit these changes using db.session.commit() and then return a response to the user:

Our car has been successfully updated.

Lastly, to delete a car, we send a DELETE request to the same endpoint. With the CarsModel object already queried, all we will need to do is use the current session to delete it by executing db.session.delete(car) and committing our transaction to reflect our changes on the database:

Conclusion

Real life applications are not as simple as ours and usually handle data that is related and spread across multiple tables.

SQLAlchemy allows us to define relationships and manipulate related data as well. More information on handling relationships can be found in the official Flask-SQLAlchemy documentation.

Our application can easily be extended to accommodate relationships and even more tables. We can also connect to multiple databases using Binds. More information on Binds can be found in the Binds documentation page.

In this post we have introduced ORMs and specifically the SQLAlchemy ORM. Using Flask and Flask-SQLAlchemy, we have created a simple API that exposes and handles data about cars as stored in a local PostgreSQL database.

The source code for the project in this post can be found on GitHub.

January 24, 2020 01:12 PM UTC

Abhijeet Pal

Python Program to Convert Octal Number to Decimal and vice-versa

The octal numeral system, or oct for short, is the base-8 number system and uses the digits 0 to 7. The main characteristic of an Octal Numbering System is that there are only 8 distinct counting digits from 0 to 7 with each digit having a weight or value of just 8 starting from the least significant bit (LSB). In the decimal number system, each digit represents the different power of 10 making them base-10 number system. Problem definition Create a python program to convert an octal number into a decimal number. Algorithm for octal to decimal conversion Take an octal number as input. Multiply each digit of the octal number starting from the last with the powers of 8 respectively. Add all the multiplied digits. The total sum gives the decimal number. Program num = input("Enter an octal number :") OctalToDecimal(int(num)) def OctalToDecimal(num): decimal_value = 0 base = 1 while (num): last_digit = num % 10 num = int(num / 10) decimal_value += last_digit * base base = base * 8 print("The decimal value is :",decimal_value) Output Enter an octal number :24 The …

The post Python Program to Convert Octal Number to Decimal and vice-versa appeared first on Django Central.

January 24, 2020 12:21 PM UTC

Peter Bengtsson

How to pad/fill a string by a variable in Python using f-strings

I often find myself Googling for this. Always a little bit embarrassed that I can't remember the incantation (syntax).

Suppose you have a string mystr that you want to fill with with spaces so it's 10 characters wide:

>>> mystr = 'peter'
>>> mystr.ljust(10)
'peter     '
>>> mystr.rjust(10)
'     peter'

Now, with "f-strings" you do:

>>> mystr = 'peter'
>>> f'{mystr:<10}'
'peter     '
>>> f'{mystr:>10}'
'     peter'

What also trips me up is, suppose that the number 10 is variable. I.e. it's not hardcoded into the f-string but a variable from somewhere else. Here's how you do it:

>>> width = 10
>>> f'{mystr:<{width}}'
'peter     '
>>> f'{mystr:>{width}}'
'     peter'

What I haven't figured out yet, is how you specify a different character than a simple single whitespace. I.e. does anybody know how to do this, but with f-strings:

>>> width = 10
>>> mystr.ljust(width, '*')
'peter*****'

January 24, 2020 03:19 AM UTC

January 23, 2020

Erik Marsja

Rename Files in Python: A Guide with Examples using os.rename()

The post Rename Files in Python: A Guide with Examples using os.rename() appeared first on Erik Marsja.

In this post, we are going to work with Python 3 to rename files. Specifically, we will use the Python module os to rename a file and rename multiple files.

First, we will rename a single file in 4 easy steps. After that, we will learn how to rename multiple files using Python 3. To be able to change the name of multiple files using Python can come in handy. For example, if we have a bunch of data files (e.g., .csv files) with long, or strange names, we may want to rename them to make working with them easier later in our projects (e.g., when loading the CSV files into a Pandas dataframe).

Example of a folder with multiple files

How to Rename a File in Python

For instance, if we have a file called python-rename-files.txt we need to know where we have stored it. There are, of course, different ways to do this. Either, we can place the Python script in the same directory and just run it to rename the file. Here’s a simple example on how to rename a file in Python:

import os
os.rename('python-rename-files.txt', 'renamed-file.txt')

4 Simple Steps to Rename a File in Python

In the first section, we are going to learn how to rename a single file in Python step-by-step. Now, the general procedure is similar when we are using Linux or Windows. However, how we go about in the first step to rename a file in Python may differ depending on which OS we use. In the renaming a file in Python examples below, we will learn how to carry on and changing names both in Linux and Windows.

1. Getting the File Path of the File we Want to Rename With Python

First, to get Python to rename a file Python needs to know where the file is located. That is, step 1 is finding the location of the file we want to change the name on.

That is, if we store our Python scripts (or Jupyter notebooks) in certain directories, we need to tell Python the complete path to the file we want to rename.

Finding the File Path in Windows

If we use Windows, we can open up the File Explorer. First, go to the folder where the file is located (e.g., “Files_To_Rename”) and click on the file path (see image below) It should look something like “C:\Users\erima96\Documents\Files_To_Rename”.

How to find the Path in Windows

Finding the File Path in Linux

Now, if we are to rename a file, using Python, in Linux we need to know the path. There are, of course, many methods to find the file path in Linux. One method is to open up a Terminal Window and use the readlink and xclip command-line applications:

readlink -f FILE_AND PATH | xclip -i

For instance, if the file we want to rename with Python is located in the folder “/home/jhf/Documents/Files_To_Rename/python-rename-files.txt” this is how we would do it:

2. Copy the Path of the File to Rename

Second, we copy the path of the file we want to rename. Note, this is as simple as just right-clicking on the path we already have marked:

Copy the file path

3. Importing the os Module

Third, we need to import a Python module called os. Luckily, this is very easy and we just type: import os. In the next step, we will actually rename a file using Python!

4. Renaming the File

Finally, we are ready to change the name of the file using the os module from Python. As the file path can be long we will create a string variable, fist, and then rename the file using os.rename. Here’s how to rename a file using Python:os.rename(PATH_TO_THE_FILE, PATH_TO_THE_NEW_FILE)

Changing a Name of a File in Windows

Here’s a full code example, for Windows users, on how to change the name of a file using Python:

import os
file_path = 'C:\\Users\\erima96\\Documents\\Files_To_Rename\\'
os.rename(file_path + 'renamed-file.txt', 
          file_path + 'python-rename-files.txt')

Note, how we added an extra ”\” to each subfolder (and at the end). In the os.rename method we also added the file_path to both the file we want to rename and the new file name (the string variable with the path to the file) and added the file name using ‘+’. If we don’t do this the file will also be moved to the folder of the Python script. If we run the above code, we can see that we have successfully renamed the file using Python:

Renaming a File in Linux

Here’s how to rename the file in Linux. Note, the file path will be a bit different (as we saw earlier when we found the file path):

import os
file_path = '/home/jhf/Documents/Files_To_Rename/python-rename-files.txt'
os.rename(file_path + 'renamed-file.txt', 
          file_path + 'python-rename-files.txt')

Now that we have learned how to rename a file in Python we are going to continue with an example in which we change the name of multiple files. As previously mentioned, renaming multiple files can come in handy if we have many files that need new names.

How to Rename Multiple Files in Python

In this section, we are going to learn how to rename multiple files in Python. There are, of course, several ways to do this. One method could be to create a Python list with all the file names that we want to change. However, if we have many files this is not an optimal way to change the name of multiple files. Thus, we are going to use another method from the os module; listdir. Furthermore, we will also use the filter method from the module called fnmatch.

The first step, before renaming the files, is to create a list of all text files in a folder (e.g., in the subfolder “Many_Files”). Note, that we have added the subfolder to the file_path string.

import os, fnmatch

file_path = 'C:\\Users\\erima96\\Documents\\Files_To_Rename\\Many_Files\\'

files_to_rename = fnmatch.filter(os.listdir(file_path), '*.txt')

print(files_to_rename)

Next, we are going to loop through each file name and rename them. In the example below, we are using the file_path string, from the code chunk above, because this is where the files are located. If we were to have the files we want to rename in a different folder, we’d change file_path to that folder. Furthermore, we are creating a new file name (e.g., new_name = ‘new_file’) and we use the enumerate method to give them a unique name. For example, the file ‘euupbihlaqgk.txt’ will be renamed ‘Datafile1.txt’.

new_name = 'Datafile'

for i, file_name in enumerate(files_to_rename):
    new_file_name = new_name + str(i) + '.txt'
    
    os.rename(file_path + file_name, 
          file_path + new_file_name)

As can be seen in the rename a file in Python example above, we also used the str() method to change the data type of the integer variable called i to a string.

Remember, if we were using Linux we’d have to change the file_path so that it will find the files we want to rename.

Renaming Multiple Files by Replacing Characters in the File Name

Now, sometimes we have files that we want to replace certain characters from. In this final example, we are going to use the replace method to replace underscores (“_”) from file names. This, of course, means that we need to rename the files.

Files with underscores

import os, fnmatch

file_path = 'C:\\Users\\erima96\\Documents\\Files_To_Rename\\Many_Files\\'

files_to_rename = fnmatch.filter(os.listdir(file_path), '*.txt')

for file_name in files_to_rename:    
    os.rename(file_path + file_name, 
          file_path + file_name.replace(' ', '-'))

Now, in the code above we have successfully replaced the “_” from the filenames using replace and then we renamed the files. Again, remember if we were to rename files in Linux the file_path string need be changed (e.g. ” “).

Underscores replaced

Conclusion: Renaming Files in Python

In this post, we have learned how to rename a single file, as well as multiple files, using Python. This was accomplished using the os and fnmatch modules. Finally, we learned how to replace underscores (and rename) files using Python.

The post Rename Files in Python: A Guide with Examples using os.rename() appeared first on Erik Marsja.

January 23, 2020 08:40 PM UTC

IslandT

Create a project to track total sales at different locations with the Python program

In the previous posts, we have gone through a project which will receive the user input and commit those data into the earning table. This program has been further modified to include the plotting of a bar chart to indicate the total sales of various inventories in various locations.

This project has been uploaded to this site, you can download the source code of this project for free through this link. If you like this project, don’t forget to award me with stars on the same project page or share the project page with friends!

Once you have downloaded the files, run the ui.py file and play around with the program.

I am using the Pandas module to plot the graph.

# begin plotting the bar chart
            s = pd.Series(index=label_x, data=label_y)
            s.plot(color="green", kind="bar", title = cc + " Sales for January at " + location)
            plt.show()

The bar chart of total sales for each inventory

Below are the steps to use the program, under the Shoe Sale and Shirt Sale section, select either the type of shoe or the shirt, then select the amount under earning and select a place under location. Just go ahead and pressed the submit button beside the shoe sale’s Combobox or else pressed the submit button beside the shirt sale’s Combobox to commit the data to the earning table!

The data we have entered are inside the earning table

In order to display the bar chart, all you need to do is to select the location under the plotting graph section and then pressed either the shoe or the shirt button within that same section.

There are more to come, you can edit the program as you wish to suit your needs. Enjoy!

January 23, 2020 04:10 PM UTC

Stack Abuse

String Formatting with Python 3's f-Strings

Introduction

Python 3.6 introduced a new way to format strings: f-Strings. It is faster than other string formatting methods in Python, and they allow us to evaluate Python expressions inside a string.

In this post, we'll look at the various ways we can format strings in Python. Then we'll have a deeper look at f-Strings, looking at how we can use it when displaying different data.

Traditional String Formatting in Python

Before we get into f-Strings, let's have a look at the more "traditional" string formatting options available in Python. If you just want to skip to learning about f-Strings, check out the section String Formatting with f-Strings in this article.

String Concatenation

String concatenation means that we are combining two strings to make a new one. In Python, we typically concatenate strings with the + operator.

In your Python interpreter, let's use concatenation to include a variable in a string:

name = "Python"
print("I like " + name + " very much!")

You would see the following output:

I like Python very much!

String concatenation works only on strings. If you want non-string data to be included, you have to convert it manually.

Let's see by concatenating a number with a string:

age = (10 + 5) * 2
print("You wouldn't believe me, but I am only " + age + " years old")

Running the above you'll see this error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can only concatenate str (not "int") to str

Now, let's convert age to a string:

age = (10 + 5) * 2
print("You wouldn't believe me, but I am only " + str(age) + " years old")

The interpreter would correctly show:

You wouldn't believe me, but I am only 30 years old

This method is not always the quickest for Python to evaluate, nor is it easy for humans to manage with many variables. It's better to use Python's dedicated string formatting methods.

C-Style String Formatting

C-style string formatting, also referred to as the printf style, uses strings as templates that are marked with % so that variables can be substituted.

For example, %d tells Python that we are substituting a number, whereas %s tells Python that we are substituting a string.

There are a few controlling mechanisms available too, for example %02d ensures that the number is at least 2 digits, and if it is not, the rest will be filled by zeros. We can use a marker like %.4f to substitute a decimal with exactly 4 floating points in the string.

In your Python interpreter, type the following code so we can see C-style string formatting in action:

print('Here is an integer %02d' % 4)
print('And a float: %.2f' % 3.141592)
print("And a %s with %d replacements" % ("mess", 2))

Your output should be:

Here is an integer 04
And a float: 3.14
And a mess with 2 replacements

As you could see, with more and more arguments it gets pretty convoluted and hard to follow. So Python takes this one step further and allows you to use dictionaries in % formatting.

Although it isn't much of an improvement in its overall aesthetics, it could help a little bit on the readability front.

Try formatting a C-style string with a dictionary:

print('Using %(dictionary)s format in C-style string formatting, here is %(num)d number to make it more interesting!' % {'dictionary': "named", "num": 1})

As you can see, we can specify the name within parenthesis between the % and the rest of the identifier.

Your interpreter should display:

Using named format in C-style string formatting, here is 1 number to make it more interesting!

If you haven't spent the last 42 years developing in C, the above syntax might not be to your liking. As such, Python gives us another option using the format() method on strings.

Python format() Function

The format() function behaves similarly to the C-style formatting, but it is much more readable. It works by invoking the format() method on your string while providing the replacements in the template within curly brackets - {}.

Using your Python interpreter, we'll use the format() method to format a string. Let's start by substituting one string:

print("This is a first {}".format("attempt!"))

The output will be:

This is a first attempt!

We can use curly brackets multiple times, substituting the variables in order:

print("And {} can add {} string too.".format("we", "more"))

Output:

And we can add more string too.

We can also name the variables we are formatting:

print("String format also supports {dictionary} arguments.".format(dictionary="named"))

The above code should print:

String format also supports named arguments.

While this method is very readable, Python is more efficient with f-Strings, while also being readable. Let's have a look at f-Strings more closely.

String Formatting with f-Strings

F-Strings, or formatted string literals, are prefixed with an f and contain the replacement fields with curly braces. They are evaluated at run-time, which makes them the fastest string formatting option in Python (at least in the standard CPython implementation).

First, verify that you have a Python version that's 3.6 or higher:

$ python3 --version
Python 3.6.0

If your Python version is less than 3.6, you need to upgrade to use this feature.

F-String literals start with an f, followed by any type of strings (i.e. single quotation, double quotation, triple quotation), then you can include your Python expression inside the string, in between curly brackets.

Let's string to use an f-String in your Python shell:

name = "f-String"
print(f"hello {name}!")

And now run it to see the magic:

hello f-String!

It's very similar to using the format() function. However, it comes with a lot of features that are not available with other formatting methods.

Let's have a look at those features, starting with multi-line strings.

Multi-line f-Strings

F-Strings allows for multi-line strings, all you have to do is wrap them in parentheses:

name = "World"
message = (
  f"Hello {name}. "
  "This is from a multi-lined f-string. "
  f"Have a good day, {name}"
)
print(message)

You will see this on printed out:

Hello World. This is from a multi-lined f-string. Have a good day, World

Don't forget to put the f literal in front of lines that have replacements. The substitutions won't work otherwise.

Evaluating Python Expressions in f-Strings

Python's f-Strings allow you to do expressions right in the string itself. The following string is valid:

number = 10
print(f"{number} + 1 = {number+1}")

And outputs:

10 + 1 = 11

You can include any valid expression you want, as long as it doesn't have special characters. For example, we can have function calls:

def func():
  return 42

print(f"func() = {func()}")

This returns:

func() = 42

Formatting Classes with f-Strings

You can include objects created from classes in an f-String. Every class has two different methods that allow an object to be converted to a string:

• The __str__() method of an object should return a string that is both displayable to the user, and understandable by them. That means it should not have any secret information that should be kept hidden from the user, and it should not have any debug messages.
• The __repr__() method of an object should return a more detailed string, possibly containing debug information.

f-Strings automatically call the __str__() for the object you provide them.

Let's try our f-Strings with a class to see for ourselves. We will create a User class that stores our name and associated database ID that our imaginary system uses.

Create a new file called fstring_classes.py and add the following:

# fstring_classes.py

class User:
    def __init__(self, name, db_id):
        self.name = name
        self.db_id = db_id

    def __str__(self):
        return f"User with name: {self.name}"

my_user = User("Sajjad", 12)
print(f"{my_user}")

In your Terminal, run the file with Python:

$ python fstring_classes.py

This program will show:

User with name: Sajjad

If we wanted to use an f-String with the __repr_() method of an object, you can put an !r in front of your object being substituted.

Edit the fstring_classes.py file and change the last line:

print(f"{my_user}")

Into the following, which includes the !r suffix:

print(f"{my_user!r}")

Now we can run this program again:

$ python fstring_classes.py

And our output will be:

User with name: Sajjad with id 12

Handling Special Characters in f-Strings

F-Strings, like any other Python string, support the use of backslashes to escape characters. All the following are valid Python f-Strings:

print(f'escaping with \\ is also possible, like: \'')

Running this will print:

escaping with \ is also possible, like: '

However, there is one limitation, we cannot use backslashes within the curly braces (the expression part of the f-String). If you try the following in your Python interpreter:

print(f'{ord("\n")}')

You'll get the following error:

  File "<stdin>", line 1
SyntaxError: f-string expression part cannot include a backslash

The same limitation is true for same-type quotation marks. The code below:

a = {"key": "value"}
print(f"the value is {a["key"]}")

Gives us this syntax error:

  File "<stdin>", line 1
    print(f"the value is {a["key"]}")
                               ^
SyntaxError: invalid syntax

To avoid these problems, we can either calculate them outside of the f-String:

ord_newline = ord("\n")
print(f'{ord_newline}')

Which prints:

10

Or we can use different quotation types:

a = {"key": "val"}
print(f"The value is {a['key']}")

Which displays:

The value is val

Conclusion

In this post, we looked at different methods of string formatting in Python, with a focus on the f-String method. In Python, we are spoiled for options as we can concatenate strings, use C-Style formatting with %, or the format() method on strings.

However, with f-Strings, we get a readable solution that Python has optimized for. Aside from its speed benefits, we've seen how well f-Strings work with evaluating expressions and objects from classes.

January 23, 2020 01:23 PM UTC

PyCon

Refund policy for Attendees and Financial Aid recipients traveling to PyCon internationally

For All International Travellers to PyCon

• If despite holding a visa you are denied entry upon arrival to the United States, then after you pursue and receive whatever refund your airline might be able to offer, PyCon wants to send you enough money to cover the rest of the cost of your airfare. You will need to document that you indeed arrived in the United States and were denied entry.
• If despite holding a visa you are denied entry upon arrival to the United States, but used our registration page to book a room in a conference hotel, our staff will personally work with the hotel to make sure you do not have to pay a cancellation fee.
• If despite holding a visa you are denied entry upon arrival to the United States, PyCon will fully refund your registration fee. While this is more serious for our conference budget — at such a late date, we will be unlikely to be able to register someone else in your place — we have decided to put the financial safety of our international travelers first.

For International Travellers who are applying for Financial Aid

• Approved financial aid applicants can ask to have their visa fee reimbursed, even if their visa is denied. See https://us.pycon.org/2020/financial-assistance/faq/#Q6 for a complete list of costs that are covered by PyCon's Financial Aid award. You should apply for your visa, if you decided to attend, right after you receive our response to your Financial Aid application (Jan 31, 2020).

• As you start the visa application process, go ahead and register for the conference. You can do so without risk: we always fully refund a registration fee when a visa application is denied. We even waive our usual $50 fee for processing a cancellation — you receive back the full registration fee that you paid!
• We advise you to delay any non-refundable travel purchases until after you have been granted a visa. Many applicants wait until they have their visa in hand before they even book a hotel room, and almost everyone waits until the visa arrives before purchasing airfare.
• Beyond those guidelines, we have historically provided only the promise that each Financial Aid recipient, if they make it to PyCon, will receive their disbursement. This obviously burdens each applicant with a risk: that if their travel plans go awry and they cannot reach Pittsburgh, that they will receive no Financial Aid. They will have to try cancelling their hotel room in time to receive a refund, and ask their airline if any kind of a refund is possible. With travel risks in mind, we have added the following stipulations to our policy:
• First, if despite holding a visa you are denied entry upon arrival to the United States, then after you pursue and receive whatever refund your airline might be able to offer, PyCon wants to send you enough of your Financial Aid grant to cover the rest of the cost of your airfare (or the whole grant, if the airfare cost more). You will need to document that you indeed arrived in the United States and were denied entry.

• Second: if despite holding a visa you are denied entry upon arrival to the United States, but used our registration page to book a room in a conference hotel, our staff will personally work with the hotel to make sure you do not receive a cancellation fee.

• Third: if despite holding a visa you are denied entry upon arrival to the United States, PyCon will fully refund your registration fee. While this is more serious for our conference budget — at such a late date, we will be unlikely to be able to register someone else in your place — we have decided to put the financial safety of our Financial Aid recipients from overseas first.

In conclusion

January 23, 2020 12:22 PM UTC

Abhijeet Pal

Python Program to Convert Binary Number to Decimal and Vice-Versa

A binary number is a number expressed in the base-2 numeral system or binary numeral system, which uses only two symbols 0 and 1. The decimal numeral system is the standard system for denoting integer and non-integer numbers. All decimal numbers can be converted to equivalent binary values and vice versa for example, the binary equivalent of “2” is “10” to explore more visit binary to decimal converter. In this article, we will create python programs for converting a binary number into decimal and vice versa Convert Binary to Decimal # Taking binary input binary = input("Enter a binary number:") # Calling the function BinaryToDecimal(binary) def BinaryToDecimal(binary): decimal = 0 for digit in binary: decimal = decimal*2 + int(digit) print("The decimal value is:", decimal) Output Enter a binary number:10 The decimal value is: 2 Pythonic way to convert binary into decimal We can use the built-in int() function to convert binary numbers into decimals. The int() function converts the binary string in base 2 number. binary_string = input("Enter a binary number :") try: decimal = int(binary_string,2) print("The decimal value is …

The post Python Program to Convert Binary Number to Decimal and Vice-Versa appeared first on Django Central.

January 23, 2020 06:04 AM UTC

Artem Rys

“Effective Python” by Brett Slatkin book review

January 23, 2020 01:32 AM UTC

January 22, 2020

Learn PyQt

Matplotlib plots in PyQt5, embedding charts in your GUI applications

pip install matplotlib

import sys
import matplotlib
matplotlib.use('Qt5Agg')

from PyQt5 import QtCore, QtWidgets

from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg
from matplotlib.figure import Figure


class MplCanvas(FigureCanvasQTAgg):

    def __init__(self, parent=None, width=5, height=4, dpi=100):
        fig = Figure(figsize=(width, height), dpi=dpi)
        self.axes = fig.add_subplot(111)
        super(MplCanvas, self).__init__(fig)


class MainWindow(QtWidgets.QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        # Create the maptlotlib FigureCanvas object, 
        # which defines a single set of axes as self.axes.
        sc = MplCanvas(self, width=5, height=4, dpi=100)
        sc.axes.plot([0,1,2,3,4], [10,1,20,3,40])
        self.setCentralWidget(sc)

        self.show()


app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
app.exec_()

Basic plot with embedded Matplotlib

import sys
import matplotlib
matplotlib.use('Qt5Agg')

from PyQt5 import QtCore, QtGui, QtWidgets

from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg, NavigationToolbar2QT as NavigationToolbar
from matplotlib.figure import Figure


class MplCanvas(FigureCanvasQTAgg):

    def __init__(self, parent=None, width=5, height=4, dpi=100):
        fig = Figure(figsize=(width, height), dpi=dpi)
        self.axes = fig.add_subplot(111)
        super(MplCanvas, self).__init__(fig)


class MainWindow(QtWidgets.QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        sc = MplCanvas(self, width=5, height=4, dpi=100)
        sc.axes.plot([0,1,2,3,4], [10,1,20,3,40])

        # Create toolbar, passing canvas as first parament, parent (self, the MainWindow) as second.
        toolbar = NavigationToolbar(sc, self)

        layout = QtWidgets.QVBoxLayout()
        layout.addWidget(toolbar)
        layout.addWidget(sc)

        # Create a placeholder widget to hold our toolbar and canvas.
        widget = QtWidgets.QWidget()
        widget.setLayout(layout)
        self.setCentralWidget(widget)

        self.show()


app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
app.exec_()

Matplotlib plot with Toolbar

Matplotlib figure options

Matplotlib curves figure options

import sys
import random
import matplotlib
matplotlib.use('Qt5Agg')

from PyQt5 import QtCore, QtWidgets

from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure


class MplCanvas(FigureCanvas):

    def __init__(self, parent=None, width=5, height=4, dpi=100):
        fig = Figure(figsize=(width, height), dpi=dpi)
        self.axes = fig.add_subplot(111)
        super(MplCanvas, self).__init__(fig)


class MainWindow(QtWidgets.QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        self.canvas = MplCanvas(self, width=5, height=4, dpi=100)
        self.setCentralWidget(self.canvas)

        n_data = 50
        self.xdata = list(range(n_data))
        self.ydata = [random.randint(0, 10) for i in range(n_data)]
        self.update_plot()

        self.show()

        # Setup a timer to trigger the redraw by calling update_plot.
        self.timer = QtCore.QTimer()
        self.timer.setInterval(100)
        self.timer.timeout.connect(self.update_plot)
        self.timer.start()

    def update_plot(self):
        # Drop off the first y element, append a new one.
        self.ydata = self.ydata[1:] + [random.randint(0, 10)]
        self.canvas.axes.cla()  # Clear the canvas.
        self.canvas.axes.plot(self.xdata, self.ydata, 'r')
        # Trigger the canvas to update and redraw.
        self.canvas.draw()


app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
app.exec_()

class MainWindow(QtWidgets.QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        self.canvas = MplCanvas(self, width=5, height=4, dpi=100)
        self.setCentralWidget(self.canvas)

        n_data = 50
        self.xdata = list(range(n_data))
        self.ydata = [random.randint(0, 10) for i in range(n_data)]

        # We need to store a reference to the plotted line 
        # somewhere, so we can apply the new data to it.
        self._plot_ref = None
        self.update_plot()

        self.show()

        # Setup a timer to trigger the redraw by calling update_plot.
        self.timer = QtCore.QTimer()
        self.timer.setInterval(100)
        self.timer.timeout.connect(self.update_plot)
        self.timer.start()

    def update_plot(self):
        # Drop off the first y element, append a new one.
        self.ydata = self.ydata[1:] + [random.randint(0, 10)]

        # Note: we no longer need to clear the axis.       
        if self._plot_ref is None:
            # First time we have no plot reference, so do a normal plot.
            # .plot returns a list of line <reference>s, as we're
            # only getting one we can take the first element.
            plot_refs = self.canvas.axes.plot(self.xdata, self.ydata, 'r')
            self._plot_ref = plot_refs[0]
        else:
            # We have a reference, we can use it to update the data for that line.
            self._plot_ref.set_ydata(self.ydata)

        # Trigger the canvas to update and redraw.
        self.canvas.draw()

plot_refs = self.canvas.axes.plot(self.xdata, self.ydata, 'r')
self._plot_ref = plot_refs[0]

self._plot_ref, = self.canvas.axes.plot(self.xdata, self.ydata, 'r')

DataFrame.plot(
    x=None, y=None, kind='line', ax=None, subplots=False,
    sharex=None, sharey=False, layout=None, figsize=None,
    use_index=True, title=None, grid=None, legend=True, style=None,
    logx=False, logy=False, loglog=False, xticks=None, yticks=None,
    xlim=None, ylim=None, rot=None, fontsize=None, colormap=None,
    table=False, yerr=None, xerr=None, secondary_y=False, 
    sort_columns=False, **kwargs
)

import sys
import matplotlib
matplotlib.use('Qt5Agg')

from PyQt5 import QtCore, QtWidgets

from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg
from matplotlib.figure import Figure

import pandas as pd


class MplCanvas(FigureCanvasQTAgg):

    def __init__(self, parent=None, width=5, height=4, dpi=100):
        fig = Figure(figsize=(width, height), dpi=dpi)
        self.axes = fig.add_subplot(111)
        super(MplCanvas, self).__init__(fig)


class MainWindow(QtWidgets.QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        # Create the maptlotlib FigureCanvas object, 
        # which defines a single set of axes as self.axes.
        sc = MplCanvas(self, width=5, height=4, dpi=100)

        # Create our pandas DataFrame with some simple
        # data and headers.
        df = pd.DataFrame([
           [0, 10], [5, 15], [2, 20], [15, 25], [4, 10], 
        ], columns=['A', 'B'])

        # plot the pandas DataFrame, passing in the 
        # matplotlib Canvas axes.
        df.plot(ax=sc.axes)

        self.setCentralWidget(sc)
        self.show()


app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
app.exec_()

Pandas plot embedded in PyQt5

import sys
import matplotlib
matplotlib.use('Qt5Agg')

from PyQt5 import QtCore, QtWidgets

from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg, NavigationToolbar2QT as NavigationToolbar
from matplotlib.figure import Figure

import pandas as pd


class MplCanvas(FigureCanvasQTAgg):

    def __init__(self, parent=None, width=5, height=4, dpi=100):
        fig = Figure(figsize=(width, height), dpi=dpi)
        self.axes = fig.add_subplot(111)
        super(MplCanvas, self).__init__(fig)


class MainWindow(QtWidgets.QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        # Create the maptlotlib FigureCanvas object, 
        # which defines a single set of axes as self.axes.
        sc = MplCanvas(self, width=5, height=4, dpi=100)

        # Create our pandas DataFrame with some simple
        # data and headers.
        df = pd.DataFrame([
           [0, 10], [5, 15], [2, 20], [15, 25], [4, 10], 
        ], columns=['A', 'B'])

        # plot the pandas DataFrame, passing in the 
        # matplotlib Canvas axes.
        df.plot(ax=sc.axes)

        # Create toolbar, passing canvas as first parament, parent (self, the MainWindow) as second.
        toolbar = NavigationToolbar(sc, self)

        layout = QtWidgets.QVBoxLayout()
        layout.addWidget(toolbar)
        layout.addWidget(sc)

        # Create a placeholder widget to hold our toolbar and canvas.
        widget = QtWidgets.QWidget()
        widget.setLayout(layout)
        self.setCentralWidget(widget)
        self.show()


app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
app.exec_()

Pandas plot with Matplotlib toolbar

January 22, 2020 09:57 PM UTC

Python Circle

Hello Word in Django: How to start with Django

Creating a hello world Django app, Starting the development of Django application in less than 5 minutes, How to start development in python Django, your first application in Django

January 22, 2020 04:46 PM UTC

Catalin George Festila

Python 3.7.5 : Django security issues - part 003.

Let's update this subject today with another new tutorial. In the last tutorial about Django security I wrote about python package named django-axes. First, let's fix an old issue about a URL pattern that matches anything and expects an integer that generates errors like: ... File "/home/mythcat/.local/lib/python3.7/site-packages/django/db/models/fields/__init__.py", line 1772, in

January 22, 2020 02:26 PM UTC

Davy Wybiral

ESP32-Cam Quickstart with Arduino Code

Learn how to add a camera to your Arduino projects the easy way using one of these cheap ESP32-Cam modules. Great for pet cams, home surveillance, time lapses, and computer vision applications.

January 22, 2020 02:15 PM UTC

Real Python

Python GUI Programming With Tkinter

Python has a lot of GUI frameworks, but Tkinter is the only framework that’s built into the Python standard library. Tkinter has several strengths. It’s cross-platform, so the same code works on Windows, macOS, and Linux. Visual elements are rendered using native operating system elements, so applications built with Tkinter look like they belong on the platform where they’re run.

Although Tkinter is considered the de-facto Python GUI framework, it’s not without criticism. One notable criticism is that GUIs built with Tkinter look outdated. If you want a shiny, modern interface, then Tkinter may not be what you’re looking for.

However, Tkinter is lightweight and relatively painless to use compared to other frameworks. This makes it a compelling choice for building GUI applications in Python, especially for applications where a modern sheen is unnecessary, and the top priority is to build something that’s functional and cross-platform quickly.

In this tutorial, you’ll learn how to:

• Get started with Tkinter with a “Hello, World!” application
• Work with widgets, such as buttons and text boxes
• Control your application layout with geometry managers
• Make your applications interactive by associating button clicks to Python functions

Once you’ve mastered these skills by working through the exercises at the end of each section, you’ll tie everything together by building two applications. The first is a temperature converter, and the second is a text editor. It’s time to dive right in and see how to build an application with Tkinter!

Building Your First Python GUI Application With Tkinter

The foundational element of a Tkinter GUI is the window. Windows are the containers in which all other GUI elements live. These other GUI elements, such as text boxes, labels, and buttons, are known as widgets. Widgets are contained inside of windows.

First, create a window that contains a single widget. Start up a new Python shell session and follow along!

$ sudo add-apt-repository ppa:deadsnakes/ppa
$ sudo apt-get update
$ sudo apt-get install python3.8 python3-tk

$ sudo apt-get install python3.8 python3-tk

With your Python shell open, the first thing you need to do is import the Python GUI Tkinter module:

>>> import tkinter as tk

A window is an instance of Tkinter’s Tk class. Go ahead and create a new window and assign it to the variable window:

>>> window = tk.Tk()

When you execute the above code, a new window pops up on your screen. How it looks depends on your operating system:

Throughout the rest of this tutorial, you’ll see Windows screenshots.

Adding a Widget

Now that you have a window, you can add a widget. Use the tk.Label class to add some text to a window. Create a Label widget with the text "Hello, Tkinter" and assign it to a variable called greeting:

>>> greeting = tk.Label(text="Hello, Tkinter")

The window you created earlier doesn’t change. You just created a Label widget, but you haven’t added it to the window yet. There are several ways to add widgets to a window. Right now, you can use the Label widget’s .pack() method:

>>> greeting.pack()

The window now looks like this:

When you .pack() a widget into a window, Tkinter sizes the window as small as it can while still fully encompassing the widget. Now execute the following:

>>> window.mainloop()

Nothing seems to happen, but notice that a new prompt does not appear in the shell.

window.mainloop() tells Python to run the Tkinter event loop. This method listens for events, such as button clicks or keypresses, and blocks any code that comes after it from running until the window it’s called on is closed. Go ahead and close the window you’ve created, and you’ll see a new prompt displayed in the shell.

Creating a window with Tkinter only takes a couple of lines of code. But blank windows aren’t very useful! In the next section, you’ll learn about some of the widgets available in Tkinter, and how you can customize them to meet your application’s needs.

Check Your Understanding

Expand the code blocks below to check your understanding:

You can expand the code block below to see a solution:

import tkinter as tk

window = tk.Tk()
label = tk.Label(text="Python rocks!")
label.pack()

window.mainloop()

When you’re ready, you can move on to the next section.

Working With Widgets

Widgets are the bread and butter of the Python GUI framework Tkinter. They are the elements through which users interact with your program. Each widget in Tkinter is defined by a class. Here are some of the widgets available:

You’ll see how to work with each of these in the following sections. Note that Tkinter has many more widgets than the ones listed here. For a full list, check out Basic Widgets and More Widgets in the TkDocs tutorial. For now, take a closer look at the Label widget.

Displaying Text and Images With Label Widgets

Label widgets are used to display text or images. The text displayed by a Label widget can’t be edited by the user. It’s for display purposes only. As you saw in the example at the beginning of this tutorial, you can create a Label widget by instantiating the Label class and passing a string to the text parameter:

label = tk.Label(text="Hello, Tkinter")

Label widgets display text with the default system text color and the default system text background color. These are typically black and white, respectively, but you may see different colors if you have changed these settings in your operating system.

You can control Label text and background colors using the foreground and background parameters:

label = tk.Label(
    text="Hello, Tkinter",
    foreground="white",  # Set the text color to white
    background="black"  # Set the background color to black
)

There are numerous valid color names, including:

• "red"
• "orange"
• "yellow"
• "green"
• "blue"
• "purple"

Many of the HTML color names work with Tkinter. A chart with most of the valid color names is available here. For a full reference, including macOS and Windows-specific system colors that are controlled by the current system theme, check out the colors manual page.

You can also specify a color using hexadecimal RGB values:

label = tk.Label(text="Hello, Tkinter", background="#34A2FE")

This sets the label background to a nice, light blue color. Hexadecimal RGB values are more cryptic than named colors, but they’re also more flexible. Fortunately, there are tools available that make getting hexadecimal color codes relatively painless.

If you don’t feel like typing out foreground and background all the time, then you can use the shorthand fg and bg parameters to set the foreground and background colors:

label = tk.Label(text="Hello, Tkinter", fg="white", bg="black")

You can also control the width and height of a label with the width and height parameters:

label = tk.Label(
    text="Hello, Tkinter",
    fg="white",
    bg="black",
    width=10,
    height=10
)

Here’s what this label looks like in a window:

It may seem strange that the label in the window isn’t square even though the width and height are both set to 10. This is because the width and height are measured in text units. One horizontal text unit is determined by the width of the character "0", or the number zero, in the default system font. Similarly, one vertical text unit is determined by the height of the character "0".

Labels are great for displaying some text, but they don’t help you get input from a user. The next three widgets that you’ll look at are all used to get user input.

Displaying Clickable Buttons With Button Widgets

Button widgets are used to display clickable buttons. They can be configured to call a function whenever they’re clicked. You’ll cover how to call functions from button clicks in the next section. For now, take a look at how to create and style a Button.

There are many similarities between Button and Label widgets. In many ways, a Button is just a Label that you can click! The same keyword arguments you use to create and style a Label will work with Button widgets. For example, the following code creates a Button with a blue background and yellow text. It also sets the width and height to 25 and 5 text units, respectively:

button = tk.Button(
    text="Click me!",
    width=25,
    height=5,
    bg="blue",
    fg="yellow",
)

Here’s what the button looks like in a window:

Pretty nifty! The next two widgets you’ll see are used to collect text input from a user.

Getting User Input With Entry Widgets

When you need to get a little bit of text from a user, like a name or an email address, use an Entry widget. They display a small text box that the user can type some text into. Creating and styling an Entry widget works pretty much exactly like Label and Button widgets. For example, the following code creates a widget with a blue background, some yellow text, and a width of 50 text units:

entry = tk.Entry(fg="yellow", bg="blue", width=50)

The interesting bit about Entry widgets isn’t how to style them, though. It’s how to use them to get input from a user. There are three main operations that you can perform with Entry widgets:

1. Retrieving text with .get()
2. Deleting text with .delete()
3. Inserting text with .insert()

The best way to get an understanding of Entry widgets is to create one and interact with it. Open up a Python shell and follow along with the examples in this section. First, import tkinter and create a new window:

>>> import tkinter as tk
>>> window = tk.Tk()

Now create a Label and an Entry widget:

>>> label = tk.Label(text="Name")
>>> entry = tk.Entry()

The Label describes what sort of text should go in the Entry widget. It doesn’t enforce any sort of requirements on the Entry, but it tells the user what your program expects them to put there. You need to .pack() the widgets into the window so that they’re visible:

>>> label.pack()
>>> entry.pack()

Here’s what that looks like:

Notice that Tkinter automatically centers the Label above the Entry widget in the window. This is a feature of .pack(), which you’ll learn more about in later sections.

Click inside the Entry widget with your mouse and type "Real Python":

Now you’ve got some text entered into the Entry widget, but that text hasn’t been sent to your program yet. You can use .get() to retrieve the text and assign it to a variable called name:

>>> name = entry.get()
>>> name
'Real Python'

You can .delete() text as well. This method takes an integer argument that tells Python which character to remove. For example, the code block below shows how .delete(0) deletes the first character from the Entry:

>>> entry.delete(0)

The text remaining in the widget is now "eal Python":

Note that, just like Python string objects, text in an Entry widget is indexed starting with 0.

If you need to remove several characters from an Entry, then pass a second integer argument to .delete() indicating the index of the character where deletion should stop. For example, the following code deletes the first four letters in the Entry:

>>> entry.delete(0, 4)

The remaining text now reads "Python":

Entry.delete() works just like string slicing. The first argument determines the starting index, and the deletion continues up to but not including the index passed as the second argument. Use the special constant tk.END for the second argument of .delete() to remove all text in an Entry:

>>> entry.delete(0, tk.END)

You’ll now see a blank text box:

On the opposite end of the spectrum, you can also .insert() text into an Entry widget:

>>> entry.insert(0, "Python")

The window now looks like this:

The first argument tells .insert() where to insert the text. If there is no text in the Entry, then the new text will always be inserted at the beginning of the widget, no matter what value you pass as the first argument. For example, calling .insert() with 100 as the first argument instead of 0, as you did above, would have generated the same output.

If an Entry already contains some text, then .insert() will insert the new text at the specified position and shift all existing text to the right:

>>> entry.insert(0, "Real ")

The widget text now reads "Real Python":

Entry widgets are great for capturing small amounts of text from a user, but because they’re only displayed on a single line, they’re not ideal for gathering large amounts of text. That’s where Text widgets come in!

Getting Multiline User Input With Text Widgets

Text widgets are used for entering text, just like Entry widgets. The difference is that Text widgets may contain multiple lines of text. With a Text widget, a user can input a whole paragraph or even several pages of text! Just like Entry widgets, there are three main operations you can perform with Text widgets:

1. Retrieve text with .get()
2. Delete text with .delete()
3. Insert text with .insert()

Although the method names are the same as the Entry methods, they work a bit differently. It’s time to get your hands dirty by creating a Text widget and seeing what all it can do.

>>> window.destroy()

In your Python shell, create a new blank window and .pack() a Text() widget into it:

>>> window = tk.Tk()
>>> text_box = tk.Text()
>>> text_box.pack()

Text boxes are much larger than Entry widgets by default. Here’s what the window created above looks like:

Click anywhere inside the window to activate the text box. Type in the word "Hello". Then press Enter and type "World" on the second line. The window should now look like this:

Just like Entry widgets, you can retrieve the text from a Text widget using .get(). However, calling .get() with no arguments doesn’t return the full text in the text box like it does for Entry widgets. It raises an exception:

>>> text_box.get()
Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    text_box.get()
TypeError: get() missing 1 required positional argument: 'index1'

Text.get() required at least one argument. Calling .get() with a single index returns a single character. To retrieve several characters, you need to pass a start index and an end index. Indices in Text widgets work differently than Entry widgets. Since Text widgets can have several lines of text, an index must contain two pieces of information:

1. The line number of a character
2. The position of a character on that line

Line numbers start with 1, and character positions start with 0. To make an index, you create a string of the form "<line>.<char>", replacing <line> with the line number and <char> with the character number. For example, "1.0" represents the first character on the first line, and "2.3" represents the fourth character on the second line.

Use the index "1.0" to get the first letter from the text box you created earlier:

>>> text_box.get("1.0")
'H'

There are five letters in the word "Hello", and the character number of o is 4, since character numbers start from 0, and the word "Hello" starts at the first position in the text box. Just like Python string slices, in order to get the entire word "Hello" from the text box, the end index must be one more than the index of the last character to be read.

So, to get the word "Hello" from the text box, use "1.0" for the first index and "1.5" for the second index:

>>> text_box.get("1.0", "1.5")
'Hello'

To get the word "World" on the second line of the text box, change the line numbers in each index to 2:

>>> text_box.get("2.0", "2.5")
'World'

To get all of the text in a text box, set the starting index in "1.0" and use the special tk.END constant for the second index:

>>> text_box.get("1.0", tk.END)
'Hello\nWorld\n'

Notice that text returned by .get() includes any newline characters. You can also see from this example that every line in a Text widget has a newline character at the end, including the last line of text in the text box.

.delete() is used to delete characters from a text box. It work just like .delete() for Entry widgets. There are two ways to use .delete():

1. With a single argument
2. With two arguments

Using the single-argument version, you pass to .delete() the index of a single character to be deleted. For example, the following deletes the first character H from the text box:

>>> text_box.delete("1.0")

The first line of text in the window now reads "ello":

With the two-argument version, you pass two indices to delete a range of characters starting at the first index and up to, but not including, the second index.

For example, to delete the remaining "ello" on the first line of the text box, use the indices "1.0" and "1.4":

>>> text_box.delete("1.0", "1.4")

Notice that the text is gone from the first line. This leaves a blank line followed the word World on the second line:

Even though you can’t see it, there’s still a character on the first line. It’s a newline character! You can verify this using .get():

>>> text_box.get("1.0")
'\n'

If you delete that character, then the rest of the contents of the text box will shift up a line:

>>> text_box.delete("1.0")

Now, "World" is on the first line of the text box:

Try to clear out the rest of the text in the text box. Set "1.0" as the start index and use tk.END for the second index:

>>> text_box.delete("1.0", tk.END)

The text box is now empty:

You can insert text into a text box using .insert():

>>> text_box.insert("1.0", "Hello")

This inserts the word "Hello" at the beginning of the text box, using the same "<line>.<column>" format used by .get() to specify the insertion position:

Check out what happens if you try to insert the word "World" on the second line:

>>> text_box.insert("2.0", "World")

Instead of inserting the text on the second line, the text is inserted at the end of the first line:

If you want to insert text onto a new line, then you need to insert a newline character manually into the string being inserted:

>>> text_box.insert("2.0", "\nWorld")

Now "World" is on the second line of the text box:

.insert() will do one of two things:

1. Insert text at the specified position if there’s already text at or after that position.
2. Append text to the specified line if the character number is greater than the index of the last character in the text box.

It’s usually impractical to try and keep track of what the index of the last character is. The best way to insert text at the end of a Text widget is to pass tk.END to the first parameter of .insert():

text_box.insert(tk.END, "Put me at the end!")

Don’t forget to include the newline character (\n) at the beginning of the text if you want to put it on a new line:

text_box.insert(tk.END, "\nPut me on a new line!")

Label, Button, Entry, and Text widgets are just a few of the widgets available in Tkinter. There are several others, including widgets for checkboxes, radio buttons, scroll bars, and progress bars. For more information on all of the available widgets, see the Additional Widgets list in the Additional Resources section.

Assigning Widgets to Frames With Frame Widgets

In this tutorial, you’re going to work with only five widgets. These are the four you’ve seen so far plus the Frame widget. Frame widgets are important for organizing the layout of your widgets in an application.

Before you get into the details about laying out the visual presentation of your widgets, take a closer look at how Frame widgets work, and how you can assign other widgets to them. The following script creates a blank Frame widget and assigns it to the main application window:

import tkinter as tk

window = tk.Tk()
frame = tk.Frame()
frame.pack()

window.mainloop()

frame.pack() packs the frame into the window so that the window sizes itself as small as possible to encompass the frame. When you run the above script, you get some seriously uninteresting output:

An empty Frame widget is practically invisible. Frames are best thought of as containers for other widgets. You can assign a widget to a frame by setting the widget’s master attribute:

frame = tk.Frame()
label = tk.Label(master=frame)

To get a feel for how this works, write a script that creates two Frame widgets called frame_a and frame_b. In this script, frame_a contains a label with the text "I'm in Frame A", and frame_b contains the label "I'm in Frame B". Here’s one way to do this:

import tkinter as tk

window = tk.Tk()

frame_a = tk.Frame()
frame_b = tk.Frame()

label_a = tk.Label(master=frame_a, text="I'm in Frame A")
label_a.pack()

label_b = tk.Label(master=frame_b, text="I'm in Frame B")
label_b.pack()

frame_a.pack()
frame_b.pack()

window.mainloop()

Note that frame_a is packed into the window before frame_b. The window that opens shows the label in frame_a above the label in frame_b:

Now see what happens when you swap the order of frame_a.pack() and frame_b.pack():

import tkinter as tk

window = tk.Tk()

frame_a = tk.Frame()
label_a = tk.Label(master=frame_a, text="I'm in Frame A")
label_a.pack()

frame_b = tk.Frame()
label_b = tk.Label(master=frame_b, text="I'm in Frame B")
label_b.pack()

# Swap the order of `frame_a` and `frame_b`
frame_b.pack()
frame_a.pack()

window.mainloop()

The output looks like this:

Now label_b is on top. Since label_b is assigned to frame_b, it moves to wherever frame_b is positioned.

All four of the widget types you’ve learned about—Label, Button, Entry, and Text—have a master attribute that’s set when you instantiate them. That way, you can control which Frame a widget is assigned to. Frame widgets are great for organizing other widgets in a logical manner. Related widgets can be assigned to the same frame so that, if the frame is ever moved in the window, then the related widgets stay together.

In addition to grouping your widgets logically, Frame widgets can add a little flare to the visual presentation of your application. Read on to see how to create various borders for Frame widgets.

Adjusting Frame Appearance With Reliefs

Frame widgets can be configured with a relief attribute that creates a border around the frame. You can set relief to be any of the following values:

• tk.FLAT: Has no border effect (the default value).
• tk.SUNKEN: Creates a sunken effect.
• tk.RAISED: Creates a raised effect.
• tk.GROOVE: Creates a grooved border effect.
• tk.RIDGE: Creates a ridged effect.

To apply the border effect, you must set the borderwidth attribute to a value greater than 1. This attribute adjusts the width of the border in pixels. The best way to get a feel for what each effect looks like is to see them for yourself. Here’s a script that packs five Frame widgets into a window, each with a different value for the relief argument:

 1 import tkinter as tk
 2 
 3 border_effects = {
 4     "flat": tk.FLAT,
 5     "sunken": tk.SUNKEN,
 6     "raised": tk.RAISED,
 7     "groove": tk.GROOVE,
 8     "ridge": tk.RIDGE,
 9 }
10 
11 window = tk.Tk()
12 
13 for relief_name, relief in border_effects.items():
14     frame = tk.Frame(master=window, relief=relief, borderwidth=5)
15     frame.pack(side=tk.LEFT)
16     label = tk.Label(master=frame, text=relief_name)
17     label.pack()
18 
19 window.mainloop()

Here’s a breakdown of this script:

• Lines 3 to 9 create a dictionary whose keys are the names of the different relief effects available in Tkinter. The values are the corresponding Tkinter objects. This dictionary is assigned to the border_effects variable.

• Line 13 starts a for loop to loop over each item in the border_effects dictionary.

• Line 14 creates a new Frame widget and assigns it to the window object. The relief attribute is set to the corresponding relief in the border_effects dictionary, and the border attribute is set to 5 so that the effect is visible.

• Line 15 packs the Frame into the window using .pack(). The side keyword argument tells Tkinter in which direction to pack the frame objects. You’ll see more about how this works in the next section.

• Lines 16 and 17 create a Label widget to display the name of the relief and pack it into the frame object you just created.

The window produced by the above script looks like this:

In this image, you can see the following effects:

• tk.FLAT creates a frame that appears to be flat.
• tk.SUNKEN adds a border that gives the frame the appearance of being sunken into the window.
• tk.RAISED gives the frame a border that makes it appear to protrude from the screen.
• tk.GROOVE adds a border that appears as a sunken groove around an otherwise flat frame.
• tk.RIDGE gives the appearance of a raised lip around the edge of the frame.

These effects give your Python GUI Tkinter application a bit of visual appeal.

Understanding Widget Naming Conventions

When you create a widget, you can give it any name you like, as long as it’s a valid Python identifier. It’s usually a good idea to include the name of the widget class in the variable name you assign to the widget instance. For example, if a Label widget is used to display a user’s name, then you might name the widget label_user_name. An Entry widget used to collect a user’s age might be called entry_age.

When you include the widget class name in the variable name, you help yourself (and anyone else that needs to read your code) to understand what type of widget the variable name refers to. However, using the full name of the widget class can lead to long variable names, so you may want to adopt a shorthand for referring to each widget type. For the rest of this tutorial, you’ll use the following shorthand prefixes to name widgets:

In this section, you learned how to create a window, use widgets, and work with frames. At this point, you can make some plain windows that display messages, but you’ve yet to create a full-blown application. In the next section, you’ll learn how to control the layout of your applications using Tkinter’s powerful geometry managers.

Check Your Understanding

Expand the code block below for an exercise to check your understanding:

You can expand the code block below to see a solution:

import tkinter as tk

window = tk.Tk()

entry = tk.Entry(width=40, bg="white", fg="black")
entry.pack()

entry.insert(0, "What is your name?")

window.mainloop()

import tkinter as tk

window = tk.Tk()

entry = tk.Entry(width=40)
entry.pack()

entry.insert(0, "What is your name?")

window.mainloop()

When you’re ready, you can move on to the next section.

Controlling Layout With Geometry Managers

Up until now, you’ve been adding widgets to windows and Frame widgets using .pack(), but you haven’t learned what exactly this method does. Let’s clear things up! Application layout in Tkinter is controlled with geometry managers. While .pack() is an example of a geometry manager, it isn’t the only one. Tkinter has two others:

• .place()
• .grid()

Each window and Frame in your application can use only one geometry manager. However, different frames can use different geometry managers, even if they’re assigned to a frame or window using another geometry manager. Start by taking a closer look at .pack().

The .pack() Geometry Manager

.pack() uses a packing algorithm to place widgets in a Frame or window in a specified order. For a given widget, the packing algorithm has two primary steps:

1. Compute a rectangular area called a parcel that’s just tall (or wide) enough to hold the widget and fills the remaining width (or height) in the window with blank space.
2. Center the widget in the parcel unless a different location is specified.

.pack() is powerful, but it can be difficult to visualize. The best way to get a feel for .pack() is to look at some examples. See what happens when you .pack() three Label widgets into a Frame:

import tkinter as tk

window = tk.Tk()

frame1 = tk.Frame(master=window, width=100, height=100, bg="red")
frame1.pack()

frame2 = tk.Frame(master=window, width=50, height=50, bg="yellow")
frame2.pack()

frame3 = tk.Frame(master=window, width=25, height=25, bg="blue")
frame3.pack()

window.mainloop()

.pack() places each Frame below the previous one by default, in the order that they’re assigned to the window:

Each Frame is placed at the top-most available position. The red Frame is placed at the top of the window. Then the yellow Frame is placed just below the red one and the blue Frame just below the yellow one.

There are three invisible parcels containing each of the three Frame widgets. Each parcel is as wide as the window and as tall as the Frame that it contains. Since no anchor point was specified when .pack() was called for each Frame, they’re all centered inside of their parcels. That’s why each Frame is centered in the window.

.pack() accepts some keyword arguments for more precisely configuring widget placement. For example, you can set the fill keyword argument to specify in which direction the frames should fill. The options are tk.X to fill in the horizontal direction, tk.Y to fill vertically, and tk.BOTH to fill in both directions. Here’s how you would stack the three frames so that each one fills the whole window horizontally:

import tkinter as tk

window = tk.Tk()

frame1 = tk.Frame(master=window, height=100, bg="red")
frame1.pack(fill=tk.X)

frame2 = tk.Frame(master=window, height=50, bg="yellow")
frame2.pack(fill=tk.X)

frame3 = tk.Frame(master=window, height=25, bg="blue")
frame3.pack(fill=tk.X)

window.mainloop()

Notice that the width is not set on any of the Frame widgets. width is no longer necessary because each frame sets .pack() to fill horizontally, overriding any width you may set.

The window produced by this script looks like this:

One of the nice things about filling the window with .pack() is that the fill is responsive to window resizing. Try widening the window generated by the previous script to see how this works. As you widen the window, the width of the three Frame widgets grow to fill the window:

Notice, though, that the Frame widgets don’t expand in the vertical direction.

The side keyword argument of .pack() specifies on which side of the window the widget should be placed. These are the available options:

• tk.TOP
• tk.BOTTOM
• tk.LEFT
• tk.RIGHT

If you don’t set side, then .pack() will automatically use tk.TOP and place new widgets at the top of the window, or at the top-most portion of the window that isn’t already occupied by a widget. For example, the following script places three frames side-by-side from left to right and expands each frame to fill the window vertically:

import tkinter as tk

window = tk.Tk()

frame1 = tk.Frame(master=window, width=200, height=100, bg="red")
frame1.pack(fill=tk.Y, side=tk.LEFT)

frame2 = tk.Frame(master=window, width=100, bg="yellow")
frame2.pack(fill=tk.Y, side=tk.LEFT)

frame3 = tk.Frame(master=window, width=50, bg="blue")
frame3.pack(fill=tk.Y, side=tk.LEFT)

window.mainloop()

This time, you have to specify the height keyword argument on at least one of the frames to force the window to have some height.

The resulting window looks like this:

Just like when you set fill=tk.X to make the frames responsive when you resized the window horizontally, you can set fill=tk.Y to make the frames responsive when you resize the window vertically:

To make the layout truly responsive, you can set an initial size for your frames using the width and height attributes. Then, set the fill keyword argument of .pack() to tk.BOTH and set the expand keyword argument to True:

import tkinter as tk

window = tk.Tk()

frame1 = tk.Frame(master=window, width=200, height=100, bg="red")
frame1.pack(fill=tk.BOTH, side=tk.LEFT, expand=True)

frame2 = tk.Frame(master=window, width=100, bg="yellow")
frame2.pack(fill=tk.BOTH, side=tk.LEFT, expand=True)

frame3 = tk.Frame(master=window, width=50, bg="blue")
frame3.pack(fill=tk.BOTH, side=tk.LEFT, expand=True)

window.mainloop()

When you run the above script, you’ll see a window that initially looks the same as the one you generated in the previous example. The difference is that now you can resize the window however you want and the frames will expand and fill the window responsively:

Pretty cool!

The .place() Geometry Manager

You can use .place() to control the precise location that a widget should occupy in a window or Frame. You must provide two keyword arguments, x and y, which specify the x- and y-coordinates for the top-left corner of the widget. Both x and y are measured in pixels, not text units.

Keep in mind that the origin (where x and y are both 0) is the top-left corner of the Frame or window. So, you can think of the y argument of .place() as the number of pixels from the top of the window, and the x argument as the number of pixels from the left of the window.

Here’s an example of how the .place() geometry manager works:

 1 import tkinter as tk
 2 
 3 window = tk.Tk()
 4 
 5 frame = tk.Frame(master=window, width=150, height=150)
 6 frame.pack()
 7 
 8 label1 = tk.Label(master=frame, text="I'm at (0, 0)", bg="red")
 9 label1.place(x=0, y=0)
10 
11 label2 = tk.Label(master=frame, text="I'm at (75, 75)", bg="yellow")
12 label2.place(x=75, y=75)
13 
14 window.mainloop()

Here’s how this code works:

• Lines 5 and 6 create a new Frame widget called frame1, one that’s 150 pixels wide and 150 pixels tall, and pack it into the window with .pack().
• Lines 8 and 9 create a new Label called label1 with a yellow background and place it in frame1 at position (0, 0).
• Lines 11 and 12 create a second Label called label2 with a red background and place it in frame1 at position (75, 75).

Here’s the window the code produces:

.place() is not used often. It has two main drawbacks:

1. Layout can be difficult to manage with .place(). This is especially true if your application has lots of widgets.
2. Layouts created with .place() are not responsive. They don’t change as the window is resized.

One of the main challenges of cross-platform GUI development is making layouts that look good no matter which platform they are viewed on, and .place() is a poor choice for making responsive and cross-platform layouts.

That’s not to say .place() should never be used! In some cases, it might be just what you need. For example, if you’re creating a GUI interface for a map, then .place() might be the perfect choice to ensure widgets are placed at the correct distance from each other on the map.

.pack() is usually a better choice than .place(), but even .pack() has some downsides. The placement of widgets depends on the order in which .pack() is called, so it can be difficult to modify existing applications without fully understanding the code controlling the layout. The .grid() geometry manager solves a lot of these issues, as you’ll see in the next section.

The .grid() Geometry Manager

The geometry manager you’ll likely use most often is .grid(), which provides all the power of .pack() in a format that’s easier to understand and maintain.

.grid() works by splitting a window or Frame into rows and columns. You specify the location of a widget by calling .grid() and passing the row and column indices to the row and column keyword arguments, respectively. Both row and column indices start at 0, so a row index of 1 and a column index of 2 tells .grid() to place a widget in the third column of the second row.

The following script creates a 3 × 3 grid of frames with Label widgets packed into them:

import tkinter as tk

window = tk.Tk()

for i in range(3):
    for j in range(3):
        frame = tk.Frame(
            master=window,
            relief=tk.RAISED,
            borderwidth=1
        )
        frame.grid(row=i, column=j)
        label = tk.Label(master=frame, text=f"Row {i}\nColumn {j}")
        label.pack()

window.mainloop()

Here’s what the resulting window looks like:

Two geometry managers are being used in this example. Each Frame is attached to the window with the .grid() geometry manager:

import tkinter as tk

window = tk.Tk()

for i in range(3):
    for j in range(3):
        frame = tk.Frame(
            master=window,
            relief=tk.RAISED,
            borderwidth=1
        )
        frame.grid(row=i, column=j)
        label = tk.Label(master=frame, text=f"Row {i}\nColumn {j}")
        label.pack()

window.mainloop()

Each label is attached to its master Frame with .pack():

import tkinter as tk

window = tk.Tk()

for i in range(3):
    for j in range(3):
        frame = tk.Frame(
            master=window,
            relief=tk.RAISED,
            borderwidth=1
        )
        frame.grid(row=i, column=j)
        label = tk.Label(master=frame, text=f"Row {i}\nColumn {j}")
        label.pack()

window.mainloop()

The important thing to realize here is that even though .grid() is called on each Frame object, the geometry manager applies to the window object. Similarly, the layout of each frame is controlled with the .pack() geometry manager.

The frames in the previous example are placed tightly next to one another. To add some space around each Frame, you can set the padding of each cell in the grid. Padding is just some blank space that surrounds a widget and separates it visually from its contents.

The two types of padding are external and internal padding. External padding adds some space around the outside of a grid cell. It’s controlled with two keyword arguments to .grid():

1. padx adds padding in the horizontal direction.
2. pady adds padding in the vertical direction.

Both padx and pady are measured in pixels, not text units, so setting both of them to the same value will create the same amount of padding in both directions. Try to add some padding around the outside of the frames in the previous example:

import tkinter as tk

window = tk.Tk()

for i in range(3):
    for j in range(3):
        frame = tk.Frame(
            master=window,
            relief=tk.RAISED,
            borderwidth=1
        )
        frame.grid(row=i, column=j, padx=5, pady=5)
        label = tk.Label(master=frame, text=f"Row {i}\nColumn {j}")
        label.pack()

window.mainloop()

Here’s the resulting window:

.pack() also has padx and pady parameters. The following code is nearly identical to the previous code, except that you add 5 pixels of additional padding around each Label in both the x and y directions:

import tkinter as tk

window = tk.Tk()

for i in range(3):
    for j in range(3):
        frame = tk.Frame(
            master=window,
            relief=tk.RAISED,
            borderwidth=1
        )
        frame.grid(row=i, column=j, padx=5, pady=5)

        label = tk.Label(master=frame, text=f"Row {i}\nColumn {j}")
        label.pack(padx=5, pady=5)

window.mainloop()

The extra padding around the Label widgets gives each cell in the grid a little bit of breathing room between the Frame border and the text in the Label:

That looks pretty nice! But if you try and expand the window in any direction, then you’ll notice that the layout isn’t very responsive:

The whole grid stays at the top-left corner as the window expands.

You can adjust how the rows and columns of the grid grow as the window is resized using .columnconfigure() and .rowconfigure() on the window object. Remember, the grid is attached to window, even though you’re calling .grid() on each Frame widget. Both .columnconfigure() and .rowconfigure() take three essential arguments:

1. The index of the grid column or row that you want to configure (or a list of indices to configure multiple rows or columns at the same time)
2. A keyword argument called weight that determines how the column or row should respond to window resizing, relative to the other columns and rows
3. A keyword argument called minsize that sets the minimum size of the row height or column width in pixels

weight is set to 0 by default, which means that the column or row doesn’t expand as the window resizes. If every column and row is given a weight of 1, then they all grow at the same rate. If one column has a weight of 1 and another a weight of 2, then the second column expands at twice the rate of the first. Adjust the previous script to better handle window resizing:

import tkinter as tk

window = tk.Tk()

for i in range(3):
    window.columnconfigure(i, weight=1, minsize=75)
    window.rowconfigure(i, weight=1, minsize=50)

    for j in range(0, 3):
        frame = tk.Frame(
            master=window,
            relief=tk.RAISED,
            borderwidth=1
        )
        frame.grid(row=i, column=j, padx=5, pady=5)

        label = tk.Label(master=frame, text=f"Row {i}\nColumn {j}")
        label.pack(padx=5, pady=5)

window.mainloop()

.columnconfigure() and .rowconfigure() are placed in the body of the outer for loop. (You could explicitly configure each column and row outside of the for loop, but that would require writing an additional six lines of code.)

On each iteration of the loop, the i-th column and row are configured to have a weight of 1. This ensures that each row and column expands at the same rate whenever the window is resized. The minsize argument is set to 75 for each column and 50 for each row. This makes sure the Label widget always displays its text without chopping off any characters, even if the window size is extremely small.

The result is a grid layout that expands and contracts smoothly as the window is resized:

Try it yourself to get a feel for how it works! Play around with the weight and minsize parameters to see how they affect the grid.

By default, widgets are centered in their grid cells. For example, the following code creates two Label widgets and places them in a grid with one column and two rows:

import tkinter as tk

window = tk.Tk()
window.columnconfigure(0, minsize=250)
window.rowconfigure([0, 1], minsize=100)

label1 = tk.Label(text="A")
label1.grid(row=0, column=0)

label2 = tk.Label(text="B")
label2.grid(row=1, column=0)

window.mainloop()

Each grid cell is 250 pixels wide and 100 pixels tall. The labels are placed in the center of each cell, as you can see in the following figure:

You can change the location of each label inside of the grid cell using the sticky parameter. sticky accepts a string containing one or more of the following letters:

• "n" or "N" to align to the top-center part of the cell
• "e" or "E" to align to the right-center side of the cell
• "s" or "S" to align to the bottom-center part of the cell
• "w" or "W" to align to the left-center side of the cell

The letters "n", "s", "e", and "w" come from the cardinal directions north, south, east, and west. Setting sticky to "n" on both Labels in the previous code positions each Label at the top-center of its grid cell:

import tkinter as tk

window = tk.Tk()
window.columnconfigure(0, minsize=250)
window.rowconfigure([0, 1], minsize=100)

label1 = tk.Label(text="A")
label1.grid(row=0, column=0, sticky="n")

label2 = tk.Label(text="B")
label2.grid(row=1, column=0, sticky="n")

window.mainloop()

Here’s the output:

You can combine multiple letters in a single string to position each Label in the corner of its grid cell:

import tkinter as tk

window = tk.Tk()
window.columnconfigure(0, minsize=250)
window.rowconfigure([0, 1], minsize=100)

label1 = tk.Label(text="A")
label1.grid(row=0, column=0, sticky="ne")

label2 = tk.Label(text="B")
label2.grid(row=1, column=0, sticky="sw")

window.mainloop()

In this example, the sticky parameter of label1 is set to "ne", which places the label at the top-right corner of its grid cell. label2 is positioned in the bottom-left corner by passing "sw" to sticky. Here’s what that looks like in the window:

When a widget is positioned with sticky, the size of the widget itself is just big enough to contain any text and other contents inside of it. It won’t fill the entire grid cell. In order to fill the grid, you can specify "ns" to force the widget to fill the cell in the vertical direction, or "ew" to fill the cell in the vertical direction. To fill the entire cell, set sticky to "nsew". The following example illustrates each of these options:

import tkinter as tk

window = tk.Tk()

window.rowconfigure(0, minsize=50)
window.columnconfigure([0, 1, 2, 3], minsize=50)

label1 = tk.Label(text="1", bg="black", fg="white")
label2 = tk.Label(text="2", bg="black", fg="white")
label3 = tk.Label(text="3", bg="black", fg="white")
label4 = tk.Label(text="4", bg="black", fg="white")

label1.grid(row=0, column=0)
label2.grid(row=0, column=1, sticky="ew")
label3.grid(row=0, column=2, sticky="ns")
label4.grid(row=0, column=3, sticky="nsew")

window.mainloop()

Here’s what the output looks like:

What the above example illustrates is that the .grid() geometry manager’s sticky parameter can be used to achieve the same effects as the .pack() geometry manager’s fill parameter. The correspondence between the sticky and fill parameters is summarized in the following table:

.grid() is a powerful geometry manager. It’s often easier to understand than .pack() and is much more flexible than .place(). When you’re creating new Tkinter applications, you should consider using .grid() as your primary geometry manager.

Now that you’ve got the fundamentals of geometry managers down for the Python GUI framework Tkinter, the next step is to assign actions to buttons to bring your applications to life.

Check Your Understanding

Expand the code block below for an exercise to check your understanding:

You can expand the code block below to see a solution:

import tkinter as tk

# Create a new window with the title "Address Entry Form"
window = tk.Tk()
window.title("Address Entry Form")

# Create a new frame `frm_form` to contain the Label
# and Entry widgets for entering address information.
frm_form = tk.Frame(relief=tk.SUNKEN, borderwidth=3)
# Pack the frame into the window
frm_form.pack()

# Create the Label and Entry widgets for "First Name"
lbl_first_name = tk.Label(master=frm_form, text="First Name:")
ent_first_name = tk.Entry(master=frm_form, width=50)
# Use the grid geometry manager to place the Label and
# Entry widgets in the first and second columns of the
# first row of the grid
lbl_first_name.grid(row=0, column=0, sticky="e")
ent_first_name.grid(row=0, column=1)

# Create the Label and Entry widgets for "Last Name"
lbl_last_name = tk.Label(master=frm_form, text="Last Name:")
ent_last_name = tk.Entry(master=frm_form, width=50)
# Place the widgets in the second row of the grid
lbl_last_name.grid(row=1, column=0, sticky="e")
ent_last_name.grid(row=1, column=1)

# Create the Label and Entry widgets for "Address Line 1"
lbl_address1 = tk.Label(master=frm_form, text="Address Line 1:")
ent_address1 = tk.Entry(master=frm_form, width=50)
# Place the widgets in the third row of the grid
lbl_address1.grid(row=2, column=0, sticky="e")
ent_address1.grid(row=2, column=1)

# Create the Label and Entry widgets for "Address Line 2"
lbl_address2 = tk.Label(master=frm_form, text="Address Line 2:")
ent_address2 = tk.Entry(master=frm_form, width=5)
# Place the widgets in the fourth row of the grid
lbl_address2.grid(row=3, column=0, sticky=tk.E)
ent_address2.grid(row=3, column=1)

# Create the Label and Entry widgets for "City"
lbl_city = tk.Label(master=frm_form, text="City:")
ent_city = tk.Entry(master=frm_form, width=50)
# Place the widgets in the fifth row of the grid
lbl_city.grid(row=4, column=0, sticky=tk.E)
ent_city.grid(row=4, column=1)

# Create the Label and Entry widgets for "State/Province"
lbl_state = tk.Label(master=frm_form, text="State/Province:")
ent_state = tk.Entry(master=frm_form, width=50)
# Place the widgets in the sixth row of the grid
lbl_state.grid(row=5, column=0, sticky=tk.E)
ent_state.grid(row=5, column=1)

# Create the Label and Entry widgets for "Postal Code"
lbl_postal_code = tk.Label(master=frm_form, text="Postal Code:")
ent_postal_code = tk.Entry(master=frm_form, width=50)
# Place the widgets in the seventh row of the grid
lbl_postal_code.grid(row=6, column=0, sticky=tk.E)
ent_postal_code.grid(row=6, column=1)

# Create the Label and Entry widgets for "Country"
lbl_country = tk.Label(master=frm_form, text="Country:")
ent_country = tk.Entry(master=frm_form, width=50)
# Place the widgets in the eight row of the grid
lbl_country.grid(row=7, column=0, sticky=tk.E)
ent_country.grid(row=7, column=1)

# Create a new frame `frm_buttons` to contain the
# Submit and Clear buttons. This frame fills the
# whole window in the horizontal direction and has
# 5 pixels of horizontal and vertical padding.
frm_buttons = tk.Frame()
frm_buttons.pack(fill=tk.X, ipadx=5, ipady=5)

# Create the "Submit" button and pack it to the
# right side of `frm_buttons`
btn_submit = tk.Button(master=frm_buttons, text="Submit")
btn_submit.pack(side=tk.RIGHT, padx=10, ipadx=10)

# Create the "Clear" button and pack it to the
# right side of `frm_buttons`
btn_clear = tk.Button(master=frm_buttons, text="Clear")
btn_clear.pack(side=tk.RIGHT, ipadx=10)

# Start the application
window.mainloop()

import tkinter as tk

# Create a new window with the title "Address Entry Form"
window = tk.Tk()
window.title("Address Entry Form")

# Create a new frame `frm_form` to contain the Label
# and Entry widgets for entering address information.
frm_form = tk.Frame(relief=tk.SUNKEN, borderwidth=3)
# Pack the frame into the window
frm_form.pack()

# List of field labels
labels = [
    "First Name:",
    "Last Name:",
    "Address Line 1:",
    "Address Line 2:",
    "City:",
    "State/Province:",
    "Postal Code:",
    "Country:",
]

# Loop over the list of field labels
for idx, text in enumerate(labels):
    # Create a Label widget with the text from the labels list
    label = tk.Label(master=frm_form, text=text)
    # Create an Entry widget
    entry = tk.Entry(master=frm_form, width=50)
    # Use the grid geometry manager to place the Label and
    # Entry widgets in the row whose index is idx
    label.grid(row=idx, column=0, sticky="e")
    entry.grid(row=idx, column=1)

# Create a new frame `frm_buttons` to contain the
# Submit and Clear buttons. This frame fills the
# whole window in the horizontal direction and has
# 5 pixels of horizontal and vertical padding.
frm_buttons = tk.Frame()
frm_buttons.pack(fill=tk.X, ipadx=5, ipady=5)

# Create the "Submit" button and pack it to the
# right side of `frm_buttons`
btn_submit = tk.Button(master=frm_buttons, text="Submit")
btn_submit.pack(side=tk.RIGHT, padx=10, ipadx=10)

# Create the "Clear" button and pack it to the
# right side of `frm_buttons`
btn_clear = tk.Button(master=frm_buttons, text="Clear")
btn_clear.pack(side=tk.RIGHT, ipadx=10)

# Start the application
window.mainloop()

When you’re ready, you can move on to the next section.

Making Your Applications Interactive

By now, you have a pretty good idea of how to create a window with Tkinter, add some widgets, and control the application layout. That’s great, but applications shouldn’t just look good—they actually need to do something! In this section, you’ll learn how to bring your applications to life by performing actions whenever certain events occur.

Using Events and Event Handlers

When you create a Tkinter application, you must call window.mainloop() to start the event loop. During the event loop, your application checks if an event has occurred. If so, then some code can be executed in response.

The event loop is provided for you with Tkinter, so you don’t have to write any code that checks for events yourself. However, you do have to write the code that will be executed in response to an event. In Tkinter, you write functions called event handlers for the events that you use in your application.

You’ll write your own event loop in order to understand better how Tkinter’s event loop works. That way, you can see how Tkinter’s event loop fits into your application, and which parts you need to write yourself.

Assume there’s a list called events_list that contains event objects. A new event object is automatically appended to events_list every time an event occurs in your program. (You don’t need to implement this updating mechanism. It just automatically happens for you in this conceptual example.) Using an infinite loop, you can continually check if there are any event objects in events_list:

# Assume that this list gets updated automatically
events_list = []

# Run the event loop
while True:
    # If events_list is empty, then no events have occurred and you
    # can skip to the next iteration of the loop
    if events_list == []:
        continue

    # If execution reaches this point, then there is at least one
    # event object in events_list
    event = events_list[0]

Right now, the event loop you’ve created doesn’t do anything with event. Let’s change that. Suppose your application needs to respond to keypresses. You need to check that event was generated by a user pressing a key on their keyboard, and, if so, pass event to an event handler function for key presses.

Assume that event has a .type attribute set to the string "keypress" if the event is a keypress event object, and a .char attribute containing the character of the key that was pressed. Create a new function handle_keypress() and update your event loop code:

events_list = []

# Create an event handler
def handle_keypress(event):
    """Print the character associated to the key pressed"""
    print(event.char)

while True:
    if events_list == []:
        continue
    event = events_list[0]

    # If event is a keypress event object
    if event.type == "keypress":
        # Call the keypress event handler
        handle_keypress(event)

When you call window.mainloop(), something like the above loop is run for you. This method takes care of two parts of the loop for you:

1. It maintains a list of events that have occurred.
2. It runs an event handler any time a new event is added to that list.

Update your event loop to use window.mainloop() instead of your own event loop:

import tkinter as tk

# Create a window object
window = tk.Tk()

# Create an event handler
def handle_keypress(event):
    """Print the character associated to the key pressed"""
    print(event.char)

# Run the event loop
window.mainloop()

.mainloop() takes care of a lot for you, but there’s something missing from the above code. How does Tkinter know when to use handle_keypress()? Tkinter widgets have a method called .bind() for just this purpose.

Using .bind()

To call an event handler whenever an event occurs on a widget, use .bind(). The event handler is said to be bound to the event because it’s called every time the event occurs. You’ll continue with the keypress example from the previous section and use .bind() to bind handle_keypress() to the keypress event:

import tkinter as tk

window = tk.Tk()

def handle_keypress(event):
    """Print the character associated to the key pressed"""
    print(event.char)

# Bind keypress event to handle_keypress()
window.bind("<Key>", handle_keypress)

window.mainloop()

Here, the handle_keypress() event handler is bound to a "<Key>" event using window.bind(). Whenever a key is pressed while the application is running, your program will print the character of the key pressed.

.bind() always takes at least two arguments:

1. An event that’s represented by a string of the form "<event_name>", where event_name can be any of Tkinter’s events
2. An event handler that’s the name of the function to be called whenever the event occurs

The event handler is bound to the widget on which .bind() is called. When the event handler is called, the event object is passed to the event handler function.

In the example above, the event handler is bound to the window itself, but you can bind an event handler to any widget in your application. For example, you can bind an event handler to a Button widget that will perform some action whenever the button is pressed:

def handle_click(event):
    print("The button was clicked!")

button = tk.Button(text="Click me!")

button.bind("<Button-1>", handle_click)

In this example, the "<Button-1>" event on the button widget is bound to the handle_click event handler. The "<Button-1>" event occurs whenever the left mouse button is pressed while the mouse is over the widget. There are other events for mouse button clicks, including "<Button-2>" for the middle mouse button and "<Button-3>" for the right mouse button.

You can bind any event handler to any kind of widget with .bind(), but there’s an easier way to bind event handlers to button clicks using the Button widget’s command attribute.

Using command

Every Button widget has a command attribute that you can assign to a function. Whenever the button is pressed, the function is executed.

Take a look at an example. First, you’ll create a window with a Label widget that holds a numerical value. You’ll put buttons on the left and right side of the label. The left button will be used to decrease the value in the Label, and the right one will increase the value. Here’s the code for the window:

import tkinter as tk

window = tk.Tk()

window.rowconfigure(0, minsize=50, weight=1)
window.columnconfigure([0, 1, 2], minsize=50, weight=1)

btn_decrease = tk.Button(master=window, text="-")
btn_decrease.grid(row=0, column=0, sticky="nsew")

lbl_value = tk.Label(master=window, text="0")
lbl_value.grid(row=0, column=1)

btn_increase = tk.Button(master=window, text="+")
btn_increase.grid(row=0, column=2, sticky="nsew")

window.mainloop()

The window looks like this:

With the app layout defined, you can bring it to life by giving the buttons some commands. Start with the left button. When this button is pressed, it should decrease the value in the label by 1. There are two things you need to know how to do in order to do this:

1. How do you get the text in a Label?
2. How do you update the text in a Label?

Label widgets don’t have .get() like Entry and Text widgets do. However, you can retrieve the text from the label by accessing the text attribute with a dictionary-style subscript notation:

label = Tk.Label(text="Hello")

# Retrieve a Label's text
text = label["text"]

# Set new text for the label
label["text"] = "Good bye"

Now that you know how to get and set a label’s text, write a function increase() that increases the value in the lbl_value by 1:

def increase():
    value = int(lbl_value["text"])
    lbl_value["text"] = f"{value + 1}"

increase() gets the text from lbl_value and converts it to an integer with int(). Then, it increases this value by 1 and sets the label’s text attribute to this new value.

You’ll also need decrease() to decrease the value in value_label by 1:

def decrease():
    value = int(lbl_value["text"])
    lbl_value["text"] = f"{value - 1}"

Put increase() and decrease() in your code just after the import statement.

To connect the buttons to the functions, assign the function to the button’s command attribute. You can do this when you instantiate the button. For example, to assign increase() to increase_button, update the line that instantiates the button to the following:

btn_increase = tk.Button(master=window, text="+", command=increase)

Now assign decrease() to decrease_button:

btn_decrease = tk.Button(master=window, text="-", command=decrease)

That’s all you need to do to bind the buttons to increase() and decrease() and make the program functional. Try saving your changes and running the application! Click the buttons to increase and decrease the value in the center of the window:

Here’s the full application code for your reference:

import tkinter as tk

def increase():
    value = int(lbl_value["text"])
    lbl_value["text"] = f"{value + 1}"


def decrease():
    value = int(lbl_value["text"])
    lbl_value["text"] = f"{value - 1}"

window = tk.Tk()

window.rowconfigure(0, minsize=50, weight=1)
window.columnconfigure([0, 1, 2], minsize=50, weight=1)

btn_decrease = tk.Button(master=window, text="-", command=decrease)
btn_decrease.grid(row=0, column=0, sticky="nsew")

lbl_value = tk.Label(master=window, text="0")
lbl_value.grid(row=0, column=1)

btn_increase = tk.Button(master=window, text="+", command=increase)
btn_increase.grid(row=0, column=2, sticky="nsew")

window.mainloop()