Async HTTP client calls in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this FastAPI async client call?

Consider this FastAPI endpoint using httpx.AsyncClient to fetch data from an external API asynchronously. What will be the response content when calling /fetch-data?

FastAPI

from fastapi import FastAPI
import httpx

app = FastAPI()

@app.get('/fetch-data')
async def fetch_data():
    async with httpx.AsyncClient() as client:
        response = await client.get('https://httpbin.org/get')
        return response.json()

A A JSON dictionary with keys like 'args', 'headers', 'origin', and 'url' from httpbin.org

B A plain text string with the raw HTML content of https://httpbin.org/get

C A runtime error because httpx.AsyncClient cannot be used inside FastAPI endpoints

D An empty JSON object {} because the response is not awaited properly

💡 Hint

Think about what response.json() returns after awaiting the HTTP GET request.

The httpx.AsyncClient fetches JSON data from the external API. Awaiting the client.get call returns a response object. Calling response.json() returns the parsed JSON dictionary. So the endpoint returns a JSON dictionary with keys like 'args', 'headers', 'origin', and 'url'.

📝 Syntax

intermediate

Which option correctly uses async HTTP client in FastAPI?

Which code snippet correctly performs an asynchronous HTTP GET request inside a FastAPI endpoint using httpx.AsyncClient?

A

client = httpx.AsyncClient()
response = await client.get('https://example.com')
return response.text

B

async with httpx.AsyncClient() as client:
    response = await client.get('https://example.com')
    return response.text

C

with httpx.AsyncClient() as client:
    response = await client.get('https://example.com')
    return response.text

D

async with httpx.AsyncClient() as client:
    response = client.get('https://example.com')
    return response.text

💡 Hint

Remember to await async calls and use async context managers properly.

Option B correctly uses async with to create the client and await to wait for the HTTP GET request. Option B misses await, so it returns a coroutine. Option B uses a synchronous context manager which is invalid for async client. Option B misses the async context manager, which can cause resource leaks.

🔧 Debug

advanced

Why does this FastAPI async client code raise an error?

Given this FastAPI endpoint, why does it raise a RuntimeError: Cannot run the event loop while another loop is running?

FastAPI

from fastapi import FastAPI
import httpx
import asyncio

app = FastAPI()

@app.get('/data')
def get_data():
    async def fetch():
        async with httpx.AsyncClient() as client:
            response = await client.get('https://httpbin.org/get')
            return response.json()
    return asyncio.run(fetch())

A Because httpx.AsyncClient() must be used synchronously, not asynchronously

B Because FastAPI endpoints cannot define inner functions

C Because the inner async function fetch() is missing the await keyword before client.get()

D Because asyncio.run() cannot be called inside an already running event loop like FastAPI's async server

💡 Hint

Think about how FastAPI runs async endpoints and event loops.

FastAPI runs on an async event loop. Calling asyncio.run() inside an already running event loop causes a RuntimeError. Instead, the endpoint itself should be async and await the async calls directly.

❓ state_output

advanced

What is the value of 'result' after this async HTTP call?

In this async function, what will be the value of result after execution?

FastAPI

import httpx

async def fetch_status():
    async with httpx.AsyncClient() as client:
        response = await client.get('https://httpbin.org/status/204')
        return response.status_code

import asyncio
result = asyncio.run(fetch_status())

A 204

B 200

C None

D Raises an HTTPError because 204 is no content

💡 Hint

Check the HTTP status code returned by the URL.

The URL https://httpbin.org/status/204 returns HTTP status code 204 (No Content). The response.status_code will be 204, which is returned and assigned to result.

🧠 Conceptual

expert

Which statement about async HTTP client calls in FastAPI is TRUE?

Choose the correct statement about using async HTTP clients like httpx.AsyncClient in FastAPI applications.

A Async HTTP clients automatically cache responses to improve performance without extra code

B Using <code>httpx.AsyncClient</code> requires running FastAPI with multiple worker processes to enable async behavior

C Using <code>httpx.AsyncClient</code> inside FastAPI endpoints improves concurrency by not blocking the event loop during HTTP calls

D FastAPI endpoints must be synchronous when using async HTTP clients to avoid runtime errors

💡 Hint

Think about how async calls help with concurrency in web servers.

Async HTTP clients like httpx.AsyncClient allow FastAPI endpoints to perform HTTP requests without blocking the event loop. This improves concurrency and scalability. Running multiple workers is unrelated to async client usage. Async clients do not cache responses automatically. FastAPI endpoints should be async to use async clients properly.