Closed
Description
The following program passes mypy type checking, but fails at runtime:
import asyncio
from typing import Awaitable
async def main() -> None:
async def coro() -> Awaitable[None]: pass
task = asyncio.create_task(coro())
asyncio.create_task(task)
asyncio.run(main())(venv) ➜ python --version
Python 3.9.6
(venv) ➜ mypy --version
mypy 0.930
(venv) ➜ mypy --strict example.py
Success: no issues found in 1 source file
(venv) ➜ python example.py
Traceback (most recent call last):
File ".../create-task-types/example.py", line 10, in <module>
asyncio.run(main())
File ".../python3.9/asyncio/runners.py", line 44, in run
return loop.run_until_complete(main)
File ".../python3.9/asyncio/base_events.py", line 642, in run_until_complete
return future.result()
File ".../create-task-types/example.py", line 7, in main
asyncio.create_task(task)
File ".../python3.9/asyncio/tasks.py", line 361, in create_task
task = loop.create_task(coro)
File ".../python3.9/asyncio/base_events.py", line 433, in create_task
task = tasks.Task(coro, loop=self, name=name)
TypeError: a coroutine was expected, got <Task pending name='Task-2' coro=<main.<locals>.coro() running at .../create-task-types/example.py:4>>