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How to build an API in Python with Flask | Python Flask Tutorial

Last updated on Dec. 14, 2020, 7:01 p.m. 6545 Views


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How to build an API in Python with Flask | Python Flask Tutorial

Last updated on Dec. 14, 2020, 7:01 p.m. 6545 Views



how to build an api with python

Creating an API in Python with Flask

Basic API or Application Programming Interface makes data access easier. This blog is all about Python APIs and Flask.

Python is a high level and object-oriented programming language. The language is known for its simple syntax and is used to build RESTful APIs. The customizable Python framework helps the developers in providing complete control over data access. Python with flask is a web “micro-framework” that is used for RESTful API development.

Many popular websites like Netflix, LinkedIn, and Pinterest have incorporated Flasks. Here we are going to explain how one can access data from the server by using the Flask application through the Python Flask Tutorial.

Before diving into deep let us understand what is API and Flasks and how you can install and use them with a Python application? You can also find the answer to the question “how to use API in python?”

Introduction to Python API

Are you familiar with the term API? APIs are used in general and for specific purposes developers also use APIs. However, a web API allows users to manipulate functionality and information over the internet. The Python or JavaScript or Python rest API of Twitter can be used to perform tasks like collecting metadata and tweet information.

In programming, the term API is a computer program that is used to be manipulated by other programs. However, with a human-written program, this is not possible. Computer programs have to communicate either with the underlying operating system or amongst themselves and APIs make this communication easier.  Here we are going to discuss web APIs of Python.

When to Create API in Python?

Mostly the APIs are created for the below-listed cases:

  • For a large data set that makes download through FTP resource-intensive or unwieldy
  • When data changes and updated frequently
  • When you need real-time data access  like for an application or other websites
  • When the user needs to perform other data related actions like data retrieval or delete or update of data.
  • Your user needs only some part of the data

APIs are used to share data with the world, they are known as the best means to share data with others. However, if the data size is small then it can be shared through a data-dump that can be in downloadable forms like in the form of JSON, CSV, XML, or SQLite file. Only a few gigabytes size can be downloaded through this method.

You can also use APIs and data dump both to provide data access to the user and they can use the best one as per their requirement.

API Terminology for API tutorial python

There are a few standard terminologies associated with APIs. Here we are going to explain to them:

URL (Uniform Resource Locator) – address of the website to access any resource like is an URL. The URL consists of a protocol (HTTPS://), the domain name of the website like ( and path (/about)

 HTTP (Hypertext Transfer Protocol): This is the initial means of data communication over the web. Several methods are implemented in HTTPS that are used to define the data movement direction and their use. The two most popular methods are GET and POST that are used respectively to access or push data from and to the server.

REST (Representational State Transfer): This philosophy of API describes the best practices to implement APIs. Specifically, we cannot define REST APIs as there are many disagreements as well for this term, so we are going to define only web APIs.

JSON(JavaScript Object Notation) is a text-based data storage format. User and machine can easily read JSON data. JSON data can be easily returned by APIs, however XML data files can also be used to return and provide data to the user.

What is Flask? Why it is used in Python?

Flask is a web framework of Python that provides the functionalities to build web applications. The functionalities like rendering templates and managing HTTP requests.

We are going to create an online python flask application in the form of a flask tutorial. If you wonder why we should use Flask, then the answer to this question is that it provides the functionality to build web applications and APIs. Django is one of the most used frameworks that have many built-in tools and a pre-set project structure to build a web application.

This is a most overwhelmed flask framework that can save the time and efforts of the experts. A blank canvas is used to write Flask applications. We here assume that you have already installed and configured Python in your system by pip.

Creating Flask Application | How to Create API in Python?

Firstly create a new folder for the project with its name and create a sub-directory named “API” within the “project” folder. Now in a text editor like Notepad++ or any other of your choice write the following code to create flask:

The code can be saved inside the API folder as an file. Now to run the application, you can use the following command:

cd projects/api

The command “pwd” can be used to check the current folder, from where you have to run your flask application. With the help of the following command you can check your api application:


If the command will run successfully then the following line will be seen as output:

*Running on (Press CTRL+C to quit)



python outputMain Phase - API Creation with Flask in Python

When we have created the flask for the web application, we can now implement the flask as API with data. We will use that is defined right in our application.

Let us define a list of Python dictionaries, in which the keys and values are grouped as pair.


‘key’: ‘value’,

‘key’: ‘value’


Here, the type of information is identified by keys like ‘id’ or ‘title’. One example of a Python dictionary with data is given below:



     'name': 'Alexander Graham Bell',

     'number': '1-333-444-5555'



     'name': 'Thomas A. Watson',

     'number': '1-444-555-6666'



Here in this phone book, there is a list of two dictionaries, where each entry consists of two keys ‘name’ and ‘number’ and they have one value associated with them that can be used to store actual information.By replacing the code of with the following code, we can get a list of dictionaries, like shown in the below code:


import flask

from flask import request, jsonify

app = flask.Flask(__name__)

app.config["DEBUG"] = True

#Create some test data for our catalog in the form of a list of dictionaries.

books = [

{'id': 0,

  'title': 'A Fire Upon the Deep',

  'author': 'Vernor Vinge',

  'first_sentence': 'The coldsleep itself was dreamless.',

  'year_published': '1992'},

{'id': 1,

  'title': 'The Ones Who Walk Away From Omelas',

  'author': 'Ursula K. Le Guin',

  'first_sentence': 'With a clamor of bells that set the swallows soaring, the Festival of Summer came to the city Omelas, bright-towered by the sea.',

  'published': '1973'},

{'id': 2,

  'title': 'Dhalgren',

  'author': 'Samuel R. Delany',

  'first_sentence': 'to wound the autumnal city.',

  'published': '1975'}


 @app.route('/', methods=['GET'])

def home():

return '''<h1>Distant Reading Archive</h1>

<p>A prototype API for distant reading of science fiction novels.</p>'''

 #A route to return all of the available entries in our catalog.

@app.route('/api/v1/resources/books/all', methods=['GET'])

def api_all():

return jsonify(books)

Now, run the code through the command: “python” from the API directory. Now through URL, you can check the new filtering capability. So when we add the url /api/v1/resources/books/all it returns the list of all books defined.


how to create api with python flask output

Final Words

Python and flasks can be easily used to build APIs. We can develop our APIs for the application requirement. Some of the benefits of using Flasks are:

  • Flasks are lightweight and minimalistic
  • Rich in documentation with lots of clear, working examples
  • Flasks are more secure
  • One who knows Python can use Flasks as well.

Flasks are used to build APIs, they are powerful and robust that can be used and make the project documentation easily as well. There are some drawbacks as well of the flasks as they do not have prefabricated components and bundled libraries. Moreover, the cost of flask customization is quite higher. Python 3 tutorial covers all of the required and essential aspects of flask and web API.

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