Python 3.7+Async programmingfunction

asyncio.run()

event loop

Runs a top-level coroutine in a new event loop. The main entry point of an async program (Python 3.7+).

Syntax

asyncio.run(coro)

You cannot call it from inside a loop that is already running — in Jupyter or within another coroutine you get RuntimeError: asyncio.run() cannot be called from a running event loop. Every call builds a fresh loop and closes it on exit, cancelling whatever is still pending, so loop-bound objects such as Queue, Lock or open connections cannot be shared across two calls. Rule of thumb: exactly one call, at the very top of your program.

Examples

import asyncio
async def main():
    return 42
result = asyncio.run(main())
result # → 42

import asyncio
async def hello():
    print('start')
    await asyncio.sleep(0)
    print('end')
asyncio.run(hello())  # → start / end

See also

Common errors

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