How to Create a Web Server in Python (Flask)

In this article, I will show you how to create a Web server using Python.

There are a number of ways to create a Web server using Python.  If you want to create something simple, like a microservice, all you need is Flask.

Step 1. Setup requirements

For this article, I am using:

• Visual Studio Code (VS Code)
• Docker
• Dev Container Extension in VS Code
• Python Version 3.10 or higher

If you are unfamiliar with dev containers, see my article:

How to use Microsoft Dev Containers (Visual Studio Code, Python)

In this article, I will show you how to use Microsoft Dev Containers to build a simple “Hello World” application in Python on a Mac.

scriptableMitch Allen

Step 2. Create a project folder

• Create a project folder:

mkdir -p ~/projects/python/flask-demo
cd ~/projects/python/flask-demo

Step 3. Start Docker

• Start Docker (open -a Docker)

• Open VS Code (note dot)

code .

Step 4. Add a .gitignore file

For this step, you will need a .gitignore extension, like the one found here:

• https://marketplace.visualstudio.com/items?itemName=codezombiech.gitignore

Once that extension is installed, do the following:

• Add a Python-specific .gitignore file
• In VS Code, call up the palette with this key combo: Cmd-Shift-P
• Type in Add gitignore and select it
• Type in Python and select it

This will generate a Python-specific .gitignore file.

Step 5. Add Dev Container

• If you don't have the dev container extension installed - see my article referenced previously
• Open the command palette (Cmd-Shift-P)
• Search for: Dev Containers: Add Dev Container Configuration Files
• Select Python 3 as the container configuration template
• If not listed, select Show All
• Select the default version (3.11 or higher)
• Click OK for any other default options
• When it appears, click Reopen in Container
• Open up the terminal window in VS Code (Ctrl-` or View / Terminal)

Step 6. Install Flask

From within the VS Code terminal window, run this command to install Flask:

pip install flask

Step 7. Create an app file

Create a new file in the root of your project called app.py.

On a Mac, you can create the new file with this command:

touch app.py

Open app.py in the editor, paste in this code, and save the file:

from flask import Flask,jsonify

# flask run

app = Flask(__name__)

@app.route('/', methods = ['GET'])
def health():
    with open('/proc/uptime', 'r') as f:
        uptime_seconds = float(f.readline().split()[0])

    data = {
        'app': __name__,
        'uptime': uptime_seconds
    }
    return jsonify(data)

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

The code does the following:

• Imports Flask from the flask package
• Also imports jsonify from the flask package
• Sets the variable app to a new Flask instance

Root response

• The combination of the decorator and the function (health()) defines an HTTP GET response for the root route (/)
• The function gets the uptime of the app
• forms a data structure for a response
• uses jsonify to convert the structure to a JSON response

Second route

• The second route defined simply returns a string of HTML to the browser.

Step 8. Run the app

In the VS Code terminal window, run the app with this command:

flask run

• If the default port (5000) is not available you can override it with the --port flag, like this:

flask run --port 3003

• If things are working correctly, click the Open in Brower button when it appears
• You should see a JSON response, similar to this (your uptime should vary):

{"app":"app","uptime":199.19}

• Browse to the other endpoint by adding it's path to the address in the browser:

http://127.0.0.1:5000/hello

You should see the simple Hello, World! message in the browser

Example Project

You can find the example project here:

• https://github.com/mitchallen/flask-demo

I've added notes to the project's README about how to freeze the installation settings and restore them via the Dev container.

Conclusion

In this article, you learned how to:

• Setup a Python dev container
• Install Flask, a simple Web server that is useful for creating microservices, etc
• Return JSON from a Flask server
• Return HTML from a Flask server
• Run the server with VS Code
• Test the server in the browser

References

• Flask Installation
• Flask: A Minimal Application
• Deploying to Production