Flask Framework

Basic Description

Flask is a micro web framework written in Python. It is classified as a microframework because it does not require particular tools or libraries. It has no database abstraction layer, form validation, or any other components where pre-existing third-party libraries provide common functions. However, Flask supports extensions that can add application features as if they were implemented in Flask itself.

Known companies that use Flask are Pinterest and LinkedIn.

More info about Flask can be found in its documentation page.

Advantages

• Flask is easier to understand and implement
• Integrated support for testing
• Flexible, you can only have the features you want thanks to its microframework approach
• Scalable, you can build a simple app and grow it later
• Helpful and well written documentation

Disadvantages

• Harder to maintain with extensions
• Community is smaller compared to Django
• Not suitable for big applications
• Need to manually add extensions about ORM, Authentication

Tutorials

We will create a simple flask app for tutorials, with external tutorial links added for more coverage of features. We will follow Flask's own documentation and tutorials but omit the details, for that its documentation page or other resources can be checked.

Other Resources:

• DigitalOcean
• Javatpoint

Setting up Flask

When setting up/installing Flask it is strongly recommended to use virtualenv. To install virtualenv:

pip install virtualenv

Then after installation, we will create a virtual environment named testenv:

mkdir test-env
cd test-env
virtualenv testenv

Then to activate the environment

source testenv/bin/activate

After creating and activating our environment we will install flask

pip install flask

Creating the application

We will create a simple "Hello, World!" application to show how to populate/create your app. We will name our file as hello.py

from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello_world():
    return "<p>Hello, World!</p>"

Running

To run our app we will export the FLASK_APP environment variable ass our app's name hello and run the framework.

export FLASK_APP=hello
flask run

Also we can set FLASK to development mode to unlock debug/development features with:

export FLASK_ENV=development

More info can be found in Flask's quick start page

Testing

For testing, generally pytest framework is used which can be installed with:

pip install pytest

After installing pytest we will create a new file called test_targetfilename.py which pytest will find automatically. For this tutorial we will use test_hello.py.

from hello import app

def test_hello():
    response = app.test_client().get('/')

    assert response.status_code == 200
    assert response.data == b'Hello, World!'

After saving the test_hello.py file, running the command py.test will automatically run the tests.

More info about testing can be found in this Flask documentation page

Example apps

There are many example applications implementing Flask framework in github. These are some repositories implementing simple Flask apps:

• Realworld Example App
• My Flask App
• Web App Tutorial

References

1. Wikipedia
2. Testing Flask App