Async batch processing in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this async batch processing code?

Consider a REST API that processes a batch of tasks asynchronously. The server returns a job ID immediately, and the client polls the job status until completion.

What will be printed by the client code below?

Rest API

import asyncio

async def check_status(job_id):
    # Simulate job completion after 3 checks
    for i in range(3):
        print(f"Checking status for job {job_id}, attempt {i+1}")
        await asyncio.sleep(0.1)
    return "completed"

async def main():
    job_id = "job123"
    status = await check_status(job_id)
    print(f"Job {job_id} status: {status}")

asyncio.run(main())

A

Checking status for job job123, attempt 1
Checking status for job job123, attempt 2
Job job123 status: completed
Checking status for job job123, attempt 3

B

Job job123 status: completed
Checking status for job job123, attempt 1
Checking status for job job123, attempt 2
Checking status for job job123, attempt 3

C

Checking status for job job123, attempt 1
Job job123 status: completed
Checking status for job job123, attempt 2
Checking status for job job123, attempt 3

D

Checking status for job job123, attempt 1
Checking status for job job123, attempt 2
Checking status for job job123, attempt 3
Job job123 status: completed

💡 Hint

Remember that await pauses the function until the awaited coroutine finishes.

The check_status function prints the status check messages sequentially with delays, then returns "completed". The main function awaits this, so all checks print before the final status print.

🧠 Conceptual

intermediate

Which HTTP method is best for submitting an async batch job to a REST API?

You want to send a batch of tasks to a REST API that will process them asynchronously. Which HTTP method should you use to submit the batch job?

A POST

B GET

C PUT

D DELETE

💡 Hint

Think about which method is used to create new resources or submit data.

POST is used to submit data to the server to create a new resource or trigger processing, which fits submitting a batch job.

🔧 Debug

advanced

Why does this async batch polling code never stop?

Look at this client code that polls a batch job status from a REST API. It never stops polling. Why?

Rest API

import asyncio
import random

async def get_status(job_id):
    # Simulate random job status
    return random.choice(["pending", "pending", "completed"])

async def poll_job(job_id):
    status = "pending"
    while status != "completed":
        status = await get_status(job_id)
        print(f"Job {job_id} status: {status}")
        await asyncio.sleep(0.1)

asyncio.run(poll_job("job456"))

A The code is missing a break statement inside the loop.

B The random choice includes "pending" twice, so it might never pick "completed".

C The await asyncio.sleep(0.1) is too short to allow status update.

D The function get_status is not awaited properly.

💡 Hint

Look at the probabilities of the status values returned.

Because "pending" is chosen twice as often as "completed", the loop might run many times before completion, but it will eventually stop. However, it can appear to never stop in short runs due to randomness.

📝 Syntax

advanced

Which option correctly defines an async function to submit a batch job and return job ID?

Choose the correct Python async function syntax that submits a batch job and returns a job ID string.

A

async def submit_batch():
    job_id = "job789"
    yield job_id

B

def async submit_batch():
    job_id = "job789"
    return job_id

C

async def submit_batch():
    job_id = "job789"
    return job_id

D

async submit_batch() -> str:
    job_id = "job789"
    return job_id

💡 Hint

Remember the correct order of keywords for async function definitions.

Option C uses the correct syntax: async def function_name():. Option C has wrong keyword order. Option C misses def. Option C uses yield which makes it an async generator, not a normal async function.

🚀 Application

expert

How many items will be in the batch result after processing this async batch?

This code submits a batch of 5 tasks asynchronously and collects results. How many items will be in the results list after completion?

Rest API

import asyncio

async def process_task(task_id):
    await asyncio.sleep(0.1)
    return f"result_{task_id}"

async def process_batch(tasks):
    results = []
    for task in tasks:
        result = await process_task(task)
        results.append(result)
    return results

batch_tasks = [1, 2, 3, 4, 5]
results = asyncio.run(process_batch(batch_tasks))
print(len(results))

A 5

B 0

C 1

D Raises an exception

💡 Hint

Each task is awaited and its result appended to the list.

The code processes each of the 5 tasks sequentially, appending one result per task, so the results list has 5 items.