Check Iterator[Span] return type annotations

[Oberon00]

From #198 (comment)

A unit test should be added to the API package that verifies one can properly use the Spans returned by various APIs as Iterator[Span] without mypy complaining.

[carlosalberto]

I started looking into this - however, even changing the signature to -> typing.ContextManager["Span"] created a rain of errors (which, I guess, we can tell mypy to ignore), i.e.

__init__.py:243: error: "bool" is invalid as return type for "__exit__" that always returns False
__init__.py:243: note: Use "typing_extensions.Literal[False]" as the return type or change it to "None"

There's also the question of how to handle the version check for typing.ContextManager (which, I think, can be simply done by checking the Python version).

[carlosalberto]

(that is, opposed to simply doing a try... except around importing it ;) cc @Oberon00 )

[Oberon00]

I think the rain of errors ⛈ was fixed in #229.

But about the try/except ImportError: I thought that was a common idiom in Python, e.g. for 2/3 compatibility?

[Oberon00]

I noticed this was still assigned to me -- unassigned, as I don't actually have this on my TODO list.

[codeboten]

Closing for now due to inactivity.