A Flask server provides the essential tools for web development—like routing URLs to your Python code—without forcing a specific structure or including non-essential features.

It has a built-in development server that’s perfect for building and testing your app. For a live website, you’d run your Flask app with a more powerful, WSGI production-ready server.

Key Concepts

• Micro Framework: Flask’s core is small and extendable. It handles the basics and lets you choose libraries for other tasks (like database access), giving you maximum flexibility.
• WSGI: It’s built on the Web Server Gateway Interface (WSGI), the standard Python interface between web servers and web applications.
• Development vs. Production Server: The server started with the flask run command is only for development. It’s not secure or efficient enough to handle real user traffic. Production apps use robust WSGI servers like Gunicorn or uWSGI.

How to Set It Up

Here’s a step-by-step guide to creating a simple “Home page” Flask application.

1. Set Up the Project and Virtual Environment

First, make sure you have Python installed. It’s a best practice to use a virtual environment to manage project dependencies separately.

Create a project folder and navigate into it

mkdir flask_server

cd flask_server

Create a virtual environment

python -m venv venv

• Activate the environment:

  • macOS/Linux: source venv/bin/activate
  • Windows: .\venv\Scripts\activate

  You’ll see (venv) appear in your command prompt.

2. Install Flask

With the virtual environment active, install Flask using pip.

pip install Flask

3. Create the Flask Application File

Create a Python file named server.py and add the following code:

Import the Flask class

from flask import Flask

# Create an instance of the app
# __name__ tells Flask where to find resources

app = Flask(__name__)

Use the route() decorator to bind a URL to a function

@app.route('/')
def index():
# The function returns the text to display in the browser
    return 'Home page'

flask --app server run

You should see output indicating the server is running:

 * Serving Flask app 'app'
 * Running on http://127.0.0.1:5000
  Press CTRL+C to quit

TIP

You can enable debug mode by run the with --debug parameter

flask --app server run --debug

The final code looks like this in the end

from flask import Flask

app = Flask(__name__)

app.route('/')
def index():
    return 'Home page'

Now, open your web browser and go to http://127.0.0.1:5000. You’ll see your “Home page” message. That’s it! You’ve successfully run a basic Flask server.