Add py.typed export per PEP 561

[maroux]

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Description of Changes

Add py.typed file and export type annotations per PEP 561 so that type testing tools like mypy can actually verify types when using arrow.

No new test added for this change and I don't think there's any documentation necessary but let me know if something needs to be added.

[codecov]

Codecov Report

Merging #925 (7e6374f) into master (5248407) will not change coverage.
The diff coverage is n/a.

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  Files           10        10           
  Lines         1896      1896           
  Branches       311       311           
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  Hits          1896      1896           

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[jadchaar]

LGTM, but I had a quick question @maroux. If PEP 561 is Python 3.7+ compatible, will mypy not detect the typings in Python 3.6?

[maroux]

@jadchaar possible? At least for mypy, it looks like it supports py.typed even for py3.6:

○ → cat a.py
import arrow


if __name__ == "__main__":
    print(arrow.get(object()))


○ → python --version
Python 3.6.11


○ → mypy a.py
a.py:5: error: No overload variant of "get" matches argument type "object"
a.py:5: note: Possible overload variant:
a.py:5: note:     def get(Union[Arrow, datetime, date, struct_time, tzinfo, int, float, str, Tuple[int, int, int]], *, locale: str = ..., tzinfo: Union[tzinfo, str, None] = ..., normalize_whitespace: bool = ...) -> Arrow
a.py:5: note:     <3 more non-matching overloads not shown>
Found 1 error in 1 file (checked 1 source file)

I think for PEPs that don't add features to python core, the python-version isn't a requirement, but I could be wrong.

[jadchaar]

@isac322 you might be more familiar with PEP 561 for type annotations. Think this is good to merge?

[isac322]

@jadchaar Yep I forgot to add this 😅

[jadchaar]

@jadchaar Yep I forgot to add this 😅

All good, just wanted to make sure!