contextvars example

example.py

import asyncio
import contextvars
import random


var = contextvars.ContextVar('var', default=1776)

all_before = set()
all_after = set()


async def do_something():
    await asyncio.sleep(random.random() * 2)
    all_before.add(var.get())

    var.set(2112)
    await asyncio.sleep(random.random() * 2)

    all_after.add(var.get())


async def driver():
    loop = asyncio.get_running_loop()

    tasks = [
        loop.create_task(do_something())
        for __ in range(100)
    ]

    await asyncio.gather(*tasks)


if __name__ == '__main__':
    asyncio.run(driver())

    print(all_before)
    print(all_after)

    assert len(all_before) == 1
    assert len(all_after) == 1