First FastAPI application - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this FastAPI endpoint?

Consider this FastAPI app code. What will the endpoint /hello return when accessed?

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get('/hello')
async def say_hello():
    return {'message': 'Hello, FastAPI!'}

A {"message": "Hello, FastAPI!"}

B "Hello, FastAPI!"

C {"hello": "message"}

D 404 Not Found error

💡 Hint

Look at the dictionary returned by the endpoint function.

The endpoint returns a JSON response with a key 'message' and value 'Hello, FastAPI!'. FastAPI automatically converts the dictionary to JSON.

📝 Syntax

intermediate

Which option will cause a syntax error in this FastAPI app?

Identify the option that will cause a syntax error when running this FastAPI app code snippet.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get('/items/{item_id}')
async def read_item(item_id: int):
    return {"item_id": item_id}

A Using async def with a return statement

B Removing the colon after the function definition line

C Changing the route decorator to @app.get('/items/{item_id}') without quotes

D Returning a dictionary from the function

💡 Hint

Check Python function syntax carefully.

Python functions require a colon at the end of the definition line. Removing it causes a SyntaxError.

❓ state_output

advanced

What is the value of counter after 3 requests?

Given this FastAPI app, what will be the value of counter after three separate requests to /count?

FastAPI

from fastapi import FastAPI

app = FastAPI()
counter = 0

@app.get('/count')
async def count():
    global counter
    counter += 1
    return {"count": counter}

A Raises an error due to global variable

B 1

C 3

D 0

💡 Hint

Think about how global variables behave in a running FastAPI app.

The global variable increments by 1 on each request, so after 3 requests it will be 3.

🔧 Debug

advanced

Why does this FastAPI app raise a runtime error?

Examine the code and select the reason for the runtime error when accessing /data.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get('/data')
def get_data():
    return await fetch_data()

def fetch_data():
    return {"data": 123}

A Using await inside a non-async function

B Missing return statement in fetch_data

C Route decorator syntax is incorrect

D fetch_data is not defined

💡 Hint

Check if the function using await is declared async.

You cannot use await inside a regular function; it must be inside an async function.

🧠 Conceptual

expert

Which option best describes FastAPI's automatic data validation?

FastAPI automatically validates request data using which feature?

A Manual checks inside endpoint functions

B Custom middleware that intercepts requests

C Using Python's built-in type hints without extra libraries

D Pydantic models that define data schemas

💡 Hint

Think about how FastAPI knows what data to expect and how to check it.

FastAPI uses Pydantic models to define and validate data automatically based on schemas.