Demonstration (via python -m asyncio):

asyncio REPL 3.9.0 (default, Oct 18 2020, 00:21:26) 
[Clang 11.0.0 (clang-1100.0.33.16)] on darwin
Use "await" directly instead of "asyncio.run()".
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>>> import asyncio
>>> from contextvars import ContextVar
>>> ctx = ContextVar('ctx')
>>> ctx.set(1)
<Token var=<ContextVar name='ctx' at 0x1021bbc70> at 0x1021bf800>
>>> ctx.get()
Traceback (most recent call last):
  File "/Users/lanfon/.pyenv/versions/3.9.0/lib/python3.9/concurrent/futures/_base.py", line 440, in result
    return self.__get_result()
  File "/Users/lanfon/.pyenv/versions/3.9.0/lib/python3.9/concurrent/futures/_base.py", line 389, in __get_result
    raise self._exception
  File "/Users/lanfon/.pyenv/versions/3.9.0/lib/python3.9/asyncio/__main__.py", line 34, in callback
    coro = func()
  File "<console>", line 1, in <module>
LookupError: <ContextVar name='ctx' at 0x1021bbc70>
>>> exit()


It also got problem inside the functions when the context is referenced in global scope.