Background tasks in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the BackgroundTasks class from FastAPI.

FastAPI

from fastapi import [1]

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

ARequest

BBackgroundTasks

CDepends

DFastAPI

Attempts:

3 left

💡 Hint

Common Mistakes

Importing the main FastAPI class instead of BackgroundTasks.

Importing unrelated classes like Request or Depends.

The BackgroundTasks class is imported from FastAPI to schedule background work.

2fill in blank

medium

Complete the function parameter to accept background tasks in a FastAPI endpoint.

FastAPI

from fastapi import BackgroundTasks

@app.post("/send")
async def send_email(background_tasks: [1]):
    pass

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

ABackgroundTasks

BRequest

CDepends

DResponse

Attempts:

3 left

💡 Hint

Common Mistakes

Using Request or Response instead of BackgroundTasks.

Forgetting to type the parameter as BackgroundTasks.

The endpoint function must accept a parameter of type BackgroundTasks to schedule background work.

3fill in blank

hard

Fix the error in scheduling a background task to call the function write_log with argument message.

FastAPI

def write_log(message: str):
    with open("log.txt", "a") as log:
        log.write(message + "\n")

@app.post("/log")
async def log_message(background_tasks: BackgroundTasks, message: str):
    background_tasks.[1](write_log, message)
    return {"message": "Log scheduled"}

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

Arun_task

Badd_background

Cschedule_task

Dadd_task

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names like add_background or run_task.

Forgetting to call the method on background_tasks.

The method to add a background task is add_task. Other names are incorrect and cause errors.

4fill in blank

hard

Fill both blanks to create a background task that writes a message and returns a confirmation.

FastAPI

def save_data(data: str):
    with open("data.txt", "a") as file:
        file.write(data + "\n")

@app.post("/save")
async def save_endpoint([1]: BackgroundTasks, data: str):
    [2].add_task(save_data, data)
    return {"status": "Data saved in background"}

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

Abackground_tasks

Brequest

Ctasks

Dbg

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for parameter and method call.

Using unrelated names like request or tasks.

The parameter name is usually background_tasks, and the same variable is used to call add_task.

5fill in blank

hard

Fill all three blanks to define a background task function, add it in the endpoint, and return a success message.

FastAPI

def [1](email: str):
    print(f"Sending email to {email}")

@app.post("/email")
async def send(email: str, [2]: BackgroundTasks):
    [2].add_task([1], email)
    return {"detail": "Email will be sent"}

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

Asend_email

Bbackground_tasks

Dsend_task

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the function and task call.

Using wrong parameter names for background tasks.

The function name is send_email. The parameter for background tasks is background_tasks. The same function name is used when adding the task.

Practice

1. What is the main purpose of using BackgroundTasks in FastAPI?

easy

A. To handle database connections synchronously

B. To replace the main event loop in FastAPI

C. To block the request until a task finishes

D. To run code after sending the response without delaying the user

Solution

1. Step 1: Understand what BackgroundTasks do

   BackgroundTasks allow running code after the response is sent, so the user is not delayed.

2. Step 2: Compare options with this behavior

   Only To run code after sending the response without delaying the user describes running code after response without delay; others describe blocking or unrelated tasks.

3. Final Answer:

   To run code after sending the response without delaying the user -> Option D

4. Quick Check:

   BackgroundTasks run code after response = B [OK]

Hint: BackgroundTasks run after response to avoid user wait [OK]

Common Mistakes:

• Thinking BackgroundTasks block the response
• Confusing BackgroundTasks with synchronous code
• Assuming BackgroundTasks replace main event loop

2. Which of the following is the correct way to add a background task in a FastAPI endpoint?

easy

A. Import BackgroundTasks but do not use it

B. Call your_function() directly inside the endpoint

C. Use background_tasks.add_task(your_function, arg1, arg2) inside the endpoint

D. Use await your_function() inside the endpoint

Solution

1. Step 1: Recall how to add background tasks in FastAPI

   You add tasks by calling background_tasks.add_task(function, args) inside the endpoint function.

2. Step 2: Check each option

   Use background_tasks.add_task(your_function, arg1, arg2) inside the endpoint correctly uses add_task. Call your_function() directly inside the endpoint calls function immediately, blocking. Use await your_function() inside the endpoint awaits function, blocking. Import BackgroundTasks but do not use it does nothing.

3. Final Answer:

   Use background_tasks.add_task(your_function, arg1, arg2) inside the endpoint -> Option C

4. Quick Check:

   Use add_task to schedule background work = D [OK]

Hint: Use add_task method on BackgroundTasks instance [OK]

Common Mistakes:

• Calling the function directly instead of scheduling
• Awaiting the function which blocks response
• Importing BackgroundTasks but not using it

3. Given this FastAPI code snippet, what will be printed after the response is sent?

from fastapi import FastAPI, BackgroundTasks

app = FastAPI()

def write_log(message: str):
    print(f"Log: {message}")

@app.get("/items/{item_id}")
async def read_item(item_id: int, background_tasks: BackgroundTasks):
    background_tasks.add_task(write_log, f"Item {item_id} accessed")
    return {"item_id": item_id}

medium

A. Log: Item {item_id} accessed is printed after response

B. Log: Item {item_id} accessed is printed before response

C. Nothing is printed because print is not awaited

D. SyntaxError because BackgroundTasks is not imported

Solution

1. Step 1: Understand background task behavior

   The function write_log is scheduled as a background task, so it runs after the response is sent.

2. Step 2: Analyze print timing

   Print inside write_log will execute after response, printing the log message with the item_id value.

3. Final Answer:

   Log: Item {item_id} accessed is printed after response -> Option A

4. Quick Check:

   Background task runs after response = C [OK]

Hint: Background tasks run after response, so print happens later [OK]

Common Mistakes:

• Thinking print runs before response
• Assuming print won't run without await
• Missing import of BackgroundTasks (actually imported here)

4. Identify the error in this FastAPI code using background tasks:

from fastapi import FastAPI, BackgroundTasks

app = FastAPI()

def send_email(email: str):
    print(f"Sending email to {email}")

@app.post("/send")
async def send(background_tasks: BackgroundTasks, email: str):
    background_tasks.add_task(send_email)
    return {"message": "Email scheduled"}

medium

A. Missing argument when adding task to background_tasks

B. BackgroundTasks should not be a parameter

C. send_email should be async

D. Email parameter must be inside the function send_email

Solution

1. Step 1: Check how add_task is called

   The function send_email requires an argument email, but add_task is called without arguments.

2. Step 2: Identify the missing argument

   The call should be background_tasks.add_task(send_email, email) to pass the email parameter.

3. Final Answer:

   Missing argument when adding task to background_tasks -> Option A

4. Quick Check:

   add_task needs function arguments = A [OK]

Hint: Pass all function args in add_task call [OK]

Common Mistakes:

• Forgetting to pass required arguments to add_task
• Thinking BackgroundTasks can't be a parameter
• Assuming send_email must be async

5. You want to log user activity and send a welcome email after a user registers. Which is the best way to do this using FastAPI background tasks?

hard

A. Call logging and email functions directly inside the endpoint synchronously

B. Add two background tasks: one for logging, one for sending email, both added via background_tasks.add_task

C. Use await on both logging and email functions inside the endpoint

D. Run logging in background task but send email synchronously

Solution

1. Step 1: Understand the goal

   We want to run both logging and sending email after response without delaying user.

2. Step 2: Evaluate options

   Add two background tasks: one for logging, one for sending email, both added via background_tasks.add_task schedules both tasks as background tasks, so they run after response. Options B and C block response. Run logging in background task but send email synchronously delays sending email.

3. Final Answer:

   Add two background tasks: one for logging, one for sending email, both added via background_tasks.add_task -> Option B

4. Quick Check:

   Schedule all post-response tasks with add_task = A [OK]

Hint: Add all post-response jobs as background tasks [OK]

Common Mistakes:

• Running tasks synchronously blocking response
• Mixing sync and async incorrectly
• Scheduling only one task in background