Async path operations in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an async GET path operation in FastAPI.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    return {"item_id": item_id, "message": "This is an async path"}

# The function must be [1]

Drag options to blanks, or click blank then click option'

Async

Bdef

Clambda

Dasync

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'def' instead of 'async def' for async path operations.

Trying to use 'sync' which is not a Python keyword.

In FastAPI, to define an asynchronous path operation, the function must be declared with 'async'.

2fill in blank

medium

Complete the code to await an async function inside a FastAPI path operation.

FastAPI

from fastapi import FastAPI
import asyncio

app = FastAPI()

async def fetch_data():
    await asyncio.sleep(1)
    return "data"

@app.get("/data")
async def get_data():
    result = [1] fetch_data()
    return {"result": result}

Drag options to blanks, or click blank then click option'

Afetch_data()

Bawait

Casync

Dyield

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the async function without 'await' causing a coroutine object to be returned.

Using 'async' instead of 'await' inside the function body.

To call an async function and wait for its result, use 'await' before the function call.

3fill in blank

hard

Fix the error in the async path operation by completing the code.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/users/{user_id}")
def get_user(user_id: int):
    return {"user_id": user_id}

# To make this async, add [1] before def

Drag options to blanks, or click blank then click option'

Aasync

Bawait

Casync def

Ddef async

Attempts:

3 left

💡 Hint

Common Mistakes

Writing 'async def' as one token in the blank instead of just 'async'.

Placing 'async' after 'def' which is invalid syntax.

To fix the error, add 'async' before 'def' to declare the function as asynchronous.

4fill in blank

hard

Fill both blanks to create an async POST path operation that receives JSON data and returns it.

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float

@app.post("/items")
async def create_item(item: [1]):
    return [2]

Drag options to blanks, or click blank then click option'

AItem

Bitem.dict()

Cdict()

DItem()

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'dict()' instead of 'item.dict()' which returns an empty dict.

Returning the model instance directly without converting to dict.

The path operation receives an 'Item' model instance and returns its dictionary representation using 'item.dict()'.

5fill in blank

hard

Fill all three blanks to define an async path operation that waits for a background task and returns a message.

FastAPI

from fastapi import FastAPI
import asyncio

app = FastAPI()

async def background_task():
    await asyncio.sleep(2)

@app.get("/wait")
async def wait_task():
    await [1]()
    return [2]

Drag options to blanks, or click blank then click option'

Abackground_task

B{"message": "Task completed"}

Cbackground_task()

D"Task completed"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'background_task()' inside await which calls the function twice.

Returning a plain string instead of a dictionary for JSON response.

You await the function name without parentheses to call it, and return a JSON message as a dictionary.

Practice

1. What is the main benefit of using async def for path operations in FastAPI?

easy

A. It makes the code run faster by using multiple CPU cores automatically.

B. It allows the app to handle many requests at the same time without waiting.

C. It forces the app to run all requests one after another in order.

D. It disables the use of await inside the function.

Solution

1. Step 1: Understand async behavior in FastAPI

   Using async def allows the server to pause on waiting tasks and handle other requests meanwhile.

2. Step 2: Compare options

   It allows the app to handle many requests at the same time without waiting. correctly describes this concurrency benefit. Options B, C, and D are incorrect because async does not automatically use multiple CPU cores, does not force sequential execution, and does not disable await.

3. Final Answer:

   It allows the app to handle many requests at the same time without waiting. -> Option B

4. Quick Check:

   Async = concurrent handling [OK]

Hint: Async means handling many requests without waiting [OK]

Common Mistakes:

• Thinking async uses multiple CPU cores automatically
• Believing async forces sequential request handling
• Confusing async with disabling await

2. Which of the following is the correct way to define an async path operation in FastAPI?

easy

A. async def read_item(): return {'item': 'value'}

B. def read_item(): return {'item': 'value'}

C. async read_item(): return {'item': 'value'}

D. def async read_item(): return {'item': 'value'}

Solution

1. Step 1: Recall async function syntax in Python

   Async functions must be declared with async def followed by the function name and parentheses.

2. Step 2: Check each option

   async def read_item(): return {'item': 'value'} uses the correct syntax. def read_item(): return {'item': 'value'} is a normal function, not async. async read_item(): return {'item': 'value'} misses def. def async read_item(): return {'item': 'value'} incorrectly places async after def.

3. Final Answer:

   async def read_item(): return {'item': 'value'} -> Option A

4. Quick Check:

   Async function = async def [OK]

Hint: Async functions start with 'async def' [OK]

Common Mistakes:

• Omitting 'def' after 'async'
• Placing 'async' after 'def'
• Using normal def instead of async def

3. Given this FastAPI async path operation, what will be the output when calling /wait?

from fastapi import FastAPI
import asyncio
app = FastAPI()

@app.get('/wait')
async def wait_seconds():
    await asyncio.sleep(1)
    return {'message': 'Done waiting'}

medium

A. Immediate {'message': 'Done waiting'} without delay

B. Empty response with status 204

C. Error because asyncio.sleep cannot be awaited

D. {'message': 'Done waiting'} after 1 second delay

Solution

1. Step 1: Understand await with asyncio.sleep

   The function pauses for 1 second asynchronously before returning the message.

2. Step 2: Determine output behavior

   After 1 second delay, the JSON response {'message': 'Done waiting'} is returned. No error occurs because asyncio.sleep is awaitable.

3. Final Answer:

   {'message': 'Done waiting'} after 1 second delay -> Option D

4. Quick Check:

   Await sleep = delayed response [OK]

Hint: Await asyncio.sleep pauses before response [OK]

Common Mistakes:

• Thinking response is immediate without delay
• Assuming asyncio.sleep is not awaitable
• Expecting empty or error response

4. Identify the error in this FastAPI async path operation:

from fastapi import FastAPI
app = FastAPI()

@app.get('/data')
def get_data():
    await fetch_data()
    return {'status': 'ok'}

medium

A. Missing async keyword before function definition

B. Missing await keyword before fetch_data()

C. fetch_data() is not defined

D. Return statement is outside the function

Solution

1. Step 1: Check function declaration with await usage

   Using await inside a function requires the function to be declared with async def.

2. Step 2: Identify the error

   The function is declared with normal def but uses await, causing a syntax error. Missing async keyword before function definition correctly identifies this.

3. Final Answer:

   Missing async keyword before function definition -> Option A

4. Quick Check:

   Await needs async def [OK]

Hint: Await inside function needs async def [OK]

Common Mistakes:

• Forgetting to add async before def
• Thinking await can be used in normal functions
• Ignoring that fetch_data() might be undefined (not focus here)

5. You want to create an async FastAPI path operation that fetches user data from a database asynchronously and returns it. Which code snippet correctly combines async path operation with awaiting a database call?

hard

A. def get_user():
user = await fetch_user_from_db()
return user

B. def get_user():
user = fetch_user_from_db()
return user

C. async def get_user():
user = await fetch_user_from_db()
return user

D. async def get_user():
user = fetch_user_from_db()
return user

Solution

1. Step 1: Understand async and await usage

   To await an async database call, the function must be async and use await before the call.

2. Step 2: Analyze each option

   async def get_user(): user = await fetch_user_from_db() return user correctly uses async def and await. def get_user(): user = fetch_user_from_db() return user is synchronous and misses await. async def get_user(): user = fetch_user_from_db() return user is async but misses await. def get_user(): user = await fetch_user_from_db() return user uses await in a normal function, which is invalid.

3. Final Answer:

   async def get_user(): user = await fetch_user_from_db() return user -> Option C

4. Quick Check:

   Async def + await call = correct pattern [OK]

Hint: Async function must await async calls inside [OK]

Common Mistakes:

• Using await in non-async functions
• Forgetting to await async calls
• Mixing sync and async code incorrectly