Build a Python Web Server with Flask

Install Flask

• Open the Terminal
• Enter the command pip3 install flask

• Make a new directory named webapp using the Terminal command mkdir webapp
• Enter the new directory with the command cd webapp

First web application =

• Open up Thonny.
• Paste the following code into Thonny.
• Save the file as app.py in the webapp directory.

from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return 'Hello world'

if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0')

Run Flask from Terminal

• Open the Terminal
• To run the app.py program enter the command python3 app.py from within the /home/pi/webapp directory
• You should see a similar response.

• Now open your web browser and enter the IP address of your Raspberry Pi.
• You can find the IP address of your Pi by hovering your mouse over the WiFi symbol.
  • Or by entering the URL localhost in the browser search bar.
  • Or entering the command ifconfig in a new Terminal window.
• You should see this response.

Local Network Web site access

• Any computer on the same local network can access your Flask web server.
• On my local network the IP address of the Raspberry Pi is 192.168.1.118
• My Mac computer can also access the Flash web server running on the Raspberry Pi by entering the IP address of the Pi in a web browser.
• The result is shown below.