Module 2 Exercises: Mastering the Foundations

You've covered a lot of ground in this module: the logic of Async, the precision of Type Hints, and the language of REST. Now, let's put it all together.

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Exercise 1: Refactoring to Type Hints

Take the following legacy Python function and refactor it to use Type Hints. Requirement: The function takes a list of integers and returns their average as a float.

# Refactor this
def calculate_average(numbers):
    total = sum(numbers)
    return total / len(numbers)

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Exercise 2: Debugging the "Thread Block"

Look at the code below. If 1,000 users call the /heavy-task endpoint at once, what will happen to the server's ability to handle other requests? How would you fix it?

import time
from fastapi import FastAPI

app = FastAPI()

@app.get("/heavy-task")
async def heavy_task():
    # Simulate a network request to an external API
    time.sleep(2) 
    return {"message": "Task complete"}

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Exercise 3: The REST Designer

You are designing an API for a Fitness App. Map out the Method, URL, and Expected Status Code (on success) for the following actions:

1. Getting a list of all user workouts.
2. Logging a brand new workout.
3. Updating a user's weight (partial update).
4. Deleting an old workout entry.

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Self-Correction / Discussion

Exercise 1 Answer:

from typing import List

def calculate_average(numbers: List[int]) -> float:
    total = sum(numbers)
    return total / len(numbers)

Exercise 2 Answer:

The server will block. Even though the function is async, time.sleep is synchronous. It will hold the event loop hostage for 2 seconds. No other requests can be handled during this time. The Fix: Use await asyncio.sleep(2) OR define the function as a standard def heavy_task() (FastAPI will then run it in a separate thread pool automatically, though asyncio is preferred for I/O).

Exercise 3 Answer:

1. GET /workouts -> 200 OK
2. POST /workouts -> 201 Created
3. PATCH /users/me/weight -> 200 OK
4. DELETE /workouts/{id} -> 204 No Content (common for deletes) or 200 OK.

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Summary of Module 2

You now have the "Language" of FastAPI under your belt. You understand:

• How Type Hints power validation.
• Why Async is critical for concurrency.
• How REST principles architecture your communication.

Well done! In Module 3: FastAPI Project Structure, we will finally stop talking theory and start building the skeleton of a production-ready application.