Add typing

[merwok]

Add type declarations (I think Python 3 native syntax, and drop 2.7 support)

Run mypy from tox

Run mypy in CI

[merwok]

@just1602 intéressé?

[just1602]

We should think about contributing typing stub file for boto3 and dotenv library.

[merwok]

Good idea! The first goal here was to make sure the store and backend classes cooperate in the right way, in complement to integration tests. Contributing a stub file to django-dotenv could be interesting!

[merwok]

@just1602 Any feedback on mypy vs pyre?

[just1602]

I didn't have the time to test yesterday. I'll have to test with ABC to see if it works with mypy. Otherwise we'll have to stay with pyre-check or open issue to mypy repo.

[merwok]

I meant: I don’t know why your PR uses pyre and not mypy, can you give details?

(independently of my inheritance/interface review)

[just1602]

@merwok because pyre handle the inheritance correctly and not mypy. Mypy give me error that the parameter self is missing when I call a method of an object.

[merwok]

That seems like a pretty fundamental Python thing to handle.
https://mypy.readthedocs.io/en/latest/cheat_sheet_py3.html#classes

Type hints cheat sheet (Python 3) — Mypy 0.650+dev.e09e72775bfeb622e67cab7d5eae0f12ef4adefa.dirty documentation

[merwok]

This is the error message:

configstore/store.py:23: error: Too few arguments for "get_setting" of "Backend"
configstore/store.py:23: error: Argument 1 to "get_setting" of "Backend" has incompatible type "str"; expected "Backend"

[just1602]

But pyre handle this gracefully. Maybe we should open an issue to see what's going on.

[merwok]

Validates if I use Tuple[Backend] without Type (after quickly checking the doc for Type that seems to be useful for more complicated setups).