> If some code is used together with timeout() and this code calls
> `.cancel()` but forgot about `.uncancel()` in try/except/finally --
> timeout() never raises TimeoutError.

Could you show an example? I'm not sure from this description who cancels whom and where the try/except/finally is in relation to the rest.

If you have something that catches CancelledError and then ignores it, e.g.

while True:
    try:
        await <something>
    except CancelledError:
        pass

then that's an immortal task and it shouldn't be run inside a timeout.

If you have something that catches CancelledError once, e.g.

try:
    await <big action>
finally:
    await <cleanup>

there should be no need to call .uncancel() *unless* the <cleanup> may hang -- in that case you could write

try:
    await <big action>
finally:
    async with timeout(5):
        await <cleanup>

I'm not sure that we should recommend using .uncancel() except in very special cases (e.g. when writing a timeout() context manager :-) and those cases should just be tested.