The docstring of windowed_complete specifies the following:

Yield ``(beginning, middle, end)`` tuples, where:

* Each ``middle`` has *n* items from *iterable*
* Each ``beginning`` has the items before the ones in ``middle``
* Each ``end`` has the items after the ones in ``middle``

It also provides an example where the iterable is of type Generator[int, None, None] and beginning, middle and end are always tuples of int. However the return type of windowed_complete is specified to be Iterator[tuple[_T, ...]]. According to this, in the example in the docstring the type of beginning, middle and end would be int, which is incorrect.

The correct return type annotation would be Iterator[tuple[tuple[_T, ...], tuple[_T, ...], tuple[_T, ...]]].