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Running a python flask app

Preparation

In VScode's terminal, create the folder flask-helloto complete the following tasks.

mkdir flask-hello
cd flask-hello

Create and run a Python flask app

Python Flask is a web framework for Python which provides functionality for building web applications. You can build websites or REST API easily with Python flask. Visit https://stackshare.io/flask to know more about the companies who are using Python Flask

In this tutorial, you will learn how to create a REST API using python flask.

First, check the version of python in the host.

python --version

What is the version of Python in the Docker host within your workspace?

Inside the flask-hello folder, create a python script app.py as follows.

import os
import socket
from flask import Flask,request,jsonify

app = Flask(__name__)

@app.route("/")
def main():
    return "Welcome Python flask!"

@app.route('/about')
def about():
    return 'I am '+socket.gethostname()

@app.route('/users')
def get_users():
    json_data = [{"name":"alice","age":18},{"name":"bob", "age": 22}]
    return jsonify(json_data),200

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000, debug=True, use_reloader=True)

The above script creates a python flask app with three endpoints.

  • / endpoint returns a string Welcome Python flask!
  • /about endpoint returns the hostname of the container
  • /users endpoint returns a JSON object with two users alice and bob

Save the file (Ctrl+S).

To run the python flask app, execute in the VSCode's terminal

python app.py

You may encounter the following error. Why?

We first initiate a Python virtual environment to install the python flask dependency for executing the app.

Execute in the terminal the following command.

virtualenv venv

If your system does have virtualenv installed, you can install it by using the pip tool.

pip install virtualenv

A folder named venv will be created for storing the libraries installed in the virtual environment.

To activate the virtual environment, execute

source venv/bin/activate

The shortcut for the above command is 

. venv/bin/activate

To install flask the Python virtual environment, execute

pip install flask

After installing the Python flask package, check the installed Python libraries with the command pip freeze.

pip freeze

To exit the virtual environment, execute

deactivate

Now, re-run the python flask app. Execute in the VSCode's terminal

python app.py

The application will listen at http://localhost:5000.

Sample output:

The python flask app has started up a web application at http://localhost:5000. If you are running this application using your own machine, you can access the application by navigating to this URL using your browser.

In GitHub Codespaces, you can navigate to the application by the URL mapped to the port 5000 at localhost.

In the browser, navigates to the / and /about and /users endpoint.

Sample output for the/users endpoint.

In the terminal running the python flask, press Ctrl+C to stop your Flask Apps.

To exit the Python virtual environment, execute

deactivate

Re-run the python flask app. 

python app.py

Can you execute the app?

Commit your work and push the changes to the remote repository

Create a new branch "task1" and commit your changes. Push the changes to the remote repository.

git checkout -b task1
git add .
git commit -m "Create a python flask app"
git push origin task1