Flask web server on Raspberry Pi - Step-by-Step Execution

Concept Flow - Flask web server on Raspberry Pi

Start Raspberry Pi

↓

Run Flask app script

↓

Flask server starts

↓

Wait for HTTP request

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Receive request

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Process request in Flask route

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Send response back

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Wait for next request or stop

The Raspberry Pi runs the Flask app script which starts a web server. It waits for web requests, processes them, and sends back responses.

Execution Sample

Raspberry Pi

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello from Pi!'

app.run(host='0.0.0.0', port=5000)

This code starts a Flask web server on the Raspberry Pi that responds with 'Hello from Pi!' when the home page is accessed.

Execution Table

Step	Action	Evaluation	Result
1	Import Flask and create app	app = Flask(__name__)	Flask app object created
2	Define route '/'	@app.route('/')	Route '/' linked to home() function
3	Define home() function	def home(): return 'Hello from Pi!'	Function ready to respond
4	Run app with host='0.0.0.0', port=5000	app.run(...)	Server starts, listens on all interfaces
5	Receive HTTP GET request at '/'	Request received	home() function called
6	Execute home()	return 'Hello from Pi!'	Response 'Hello from Pi!' sent
7	Wait for next request	Idle	Server running
8	Stop server (Ctrl+C)	Interrupt signal	Server stops

💡 Server stops when interrupted or Raspberry Pi shuts down

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 6	Final
app	None	Flask app object	Flask app object with route '/'	Same	Server running	Same	Server stopped

Key Moments - 3 Insights

Why do we use host='0.0.0.0' in app.run()?

Using host='0.0.0.0' makes the Flask server listen on all network interfaces, allowing other devices on the network to access the Raspberry Pi server. See execution_table step 4.

What happens if we don't define a route with @app.route?

Without defining a route, Flask won't know which function to call for a URL, so requests to that URL will return 404 errors. See execution_table step 2.

How does Flask handle multiple requests?

Flask runs a simple server that processes one request at a time by default, waiting for each request to finish before handling the next. See execution_table steps 5-7.

Visual Quiz - 3 Questions

Look at the execution_table, what is the server doing at step 7?

A Processing a request

B Waiting for the next request

C Starting the Flask app

D Stopping the server

💡 Hint

Check the 'Action' and 'Result' columns at step 7 in execution_table

At which step does the Flask app start listening on the network?

A Step 2

B Step 6

C Step 4

D Step 8

💡 Hint

Look for when app.run() is called in execution_table

If we change host='127.0.0.1' in app.run(), what changes in the server behavior?

A Server listens only on the Raspberry Pi itself

B Server listens on all network interfaces

C Server stops immediately

D Server listens on port 80

💡 Hint

Refer to key_moments about host='0.0.0.0' and network access

Concept Snapshot

Flask web server on Raspberry Pi:
- Import Flask and create app object
- Define routes with @app.route decorator
- Run app with app.run(host='0.0.0.0', port=5000) to listen on all interfaces
- Server waits for HTTP requests and responds
- Stop server with interrupt (Ctrl+C)

Full Transcript

This visual execution shows how to run a Flask web server on a Raspberry Pi. First, the Flask app object is created. Then, a route '/' is defined with a function that returns a greeting. Running app.run with host='0.0.0.0' starts the server listening on all network interfaces, allowing other devices to connect. When a request comes to '/', Flask calls the function and sends back the response. The server waits for more requests until stopped. Key points include why host='0.0.0.0' is used and how routes connect URLs to functions.