Summary - Asyncio

Combine gather, Queue and Semaphore to write a web scraper.

Summary - Asyncio

This group covered asyncio's concurrent tools. gather awaits all; wait gives done/pending sets; Queue for producer-consumer; Lock protects a critical section; Semaphore controls the concurrency limit.

The final task combines gather and Semaphore: you'll await several coroutines limited by Semaphore.

Exercise gather + Semaphore combined

Start with import asyncio. Define sem = asyncio.Semaphore(2). The function async def fetch(n) returns n * 2 inside async with sem:. Inside async def main() call return await asyncio.gather(fetch(1), fetch(2), fetch(3)). Add print(asyncio.run(main())).

Show example solution

import asyncio

sem = asyncio.Semaphore(2)

async def fetch(n):
    async with sem:
        return n * 2

async def main():
    return await asyncio.gather(fetch(1), fetch(2), fetch(3))

print(asyncio.run(main()))

Test yourself

Which function awaits all completions?
- asyncio.wait
- asyncio.Queue
- asyncio.gather
- asyncio.Lock
Show answer

asyncio.gather — asyncio.gather awaits all coroutines.

Summary: Semaphore

sem = asyncio.____(2)

Show answer

sem = asyncio.Semaphore(2)

Match the group tools

gather

Awaits all
wait

Gives done/pending
Queue

Passes data
Semaphore

Limits permits

Next lesson: urllib

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