Accepting connections in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a FastAPI app receives a GET request?

Consider a FastAPI app with this route:

from fastapi import FastAPI
app = FastAPI()

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

What is the output when a client sends a GET request to /hello?

FastAPI

from fastapi import FastAPI
app = FastAPI()

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

A The server responds with plain text: Hello!

B The server responds with JSON: {"message": "Hello!"}

C The server returns a 404 Not Found error

D The server crashes with a runtime error

💡 Hint

Think about what the return value of the route function means in FastAPI.

FastAPI automatically converts the returned dictionary into JSON and sends it as the response body with the correct content type.

📝 Syntax

intermediate

Which code correctly starts a FastAPI server on port 8080?

You want to run your FastAPI app on port 8080 using uvicorn. Which code snippet below does this correctly?

A uvicorn.run(app, port=8080, host="localhost")

B uvicorn.run(app, "0.0.0.0", 8080)

C uvicorn.run(app, host="0.0.0.0", port=8080)

D uvicorn.run(app, port="8080", host=0.0.0.0)

💡 Hint

Check the parameter names and types uvicorn.run expects.

uvicorn.run requires host as a string and port as an integer. Option C uses correct parameter names and types.

🔧 Debug

advanced

Why does this FastAPI app fail to accept connections?

Given this code:

from fastapi import FastAPI
app = FastAPI()

@app.get("/")
def read_root():
    return {"msg": "Hi"}

You run uvicorn main:app but get no response on http://localhost:8000/. What is the likely cause?

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get("/")
def read_root():
    return {"msg": "Hi"}

A The app variable is not named correctly for uvicorn to find

B The route function is not async, so uvicorn ignores it

C The server is not running because uvicorn was not installed

D The server is running but the route returns a 404 because of a typo

💡 Hint

Check the command and the app variable name in the code.

uvicorn expects the app variable to be named exactly as specified after the colon. If the app variable name is different, uvicorn won't find it.

❓ state_output

advanced

What is the output after multiple requests to this FastAPI app?

Consider this FastAPI app:

from fastapi import FastAPI
app = FastAPI()
counter = 0

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

If a client sends 3 GET requests to /count in a row, what is the JSON response to the third request?

FastAPI

from fastapi import FastAPI
app = FastAPI()
counter = 0

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

A The server crashes with a runtime error

B {"count": 1}

C {"count": 0}

D {"count": 3}

💡 Hint

Think about how the global variable changes with each request.

The global counter increments by 1 on each request. After 3 requests, it will be 3.

🧠 Conceptual

expert

Which statement about FastAPI connection handling is true?

FastAPI uses ASGI servers like uvicorn to accept connections. Which of these statements is correct?

A FastAPI can handle many connections concurrently using async functions and event loop

B FastAPI requires all route functions to be synchronous to accept connections

C FastAPI automatically retries failed connections without developer code

D FastAPI handles connections synchronously, blocking other requests until one finishes

💡 Hint

Think about how async functions and ASGI servers work together.

FastAPI leverages async functions and ASGI servers to handle many connections at once without blocking.