Support for static typing

[markedwards]

Is there any plan to add static type hints to the Pytest code base, or to support/bless a typeshed implementation? Or is this already solved and my Google skills have failed me?

[RonnyPfannschmidt]

its currently unsolved and hasnt been discussed in depth by the wider set of pytest core contributors,

its not clear how and in what time frames to progress

[nicoddemus]

@markedwards I suppose you mean adding support so things like @pytest.fixture can accept type hints right?

I don't know, it feels to get the most bang for the buck we would need to be Python 3 only to be able to use native type hints instead of hints in comments (I'm aware it is possible to use type hints in Python 2). Perhaps when we drop Python 2 we can start thinking about this?

[The-Compiler]

I think @markedwards means adding type annotations to pytest's API (in the core or in the typeshed repository), so users of pytest can e.g. use mypy to tell them if they're using pytest's API incorrectly.

[markedwards]

Thanks everyone. Yes @The-Compiler that’s what I meant. I’m sure there are wrinkles that I haven’t considered, so I’ll just leave this as a general request for type hint support, and the developers can determine what exactly that should mean.

[nicoddemus]

I think @markedwards means adding type annotations to pytest's API (in the core or in the typeshed repository), so users of pytest can e.g. use mypy to tell them if they're using pytest's API incorrectly.

I expressed myself badly, sorry, that is what I meant. (reading my reply again I can see how it actually means something completely different).

I think one can contribute the pytest API to the typeshed repository right away without having to change pytest, I've done so for the deprecated python-skeletons repository (the work done there can be used as a starting point btw).

[gaborbernat]

@nicoddemus here's my use case, imagine I want to type hint my test code:

def test_magic(tmpdir, caplog, monekypatch):
    pass

To be able to do type hint I need the fixture types to be exposed publicly (otherwise I need to import private stuff from Pytest which leaves me exposed; e.g. CaptureFixture in the above example).

# private type imports; oh no!!!
from _pytest.capture import CaptureFixture
from _pytest.monkeypatch import MonkeyPatch
from py._path.local import LocalPath

def test_magic(tmpdir: LocalPath, caplog: CaptureFixture, monekypatch: MonkeyPatch):
    pass

Maybe we should have beside the https://github.com/pytest-dev/pytest/blob/master/src/pytest.py a pytest.fixture_types a module that exposes those? Users are already relying on their interfaces in the tests, so those are already somewhat public; not?

I also propose to split these two issues:

1. type hint pytest code
2. provide stubs to type hint test code written against pytest.

[gaborbernat]

@RonnyPfannschmidt @nicoddemus @asottile ping :-)

[asottile]

my 2c:

• exposing a convenient public module for the private types seems like a good idea 👍
• providing stubs in typeshed also seems like a good idea 👍 (iirc all that's needed here is pytest's project sign off)
• personally I really dislike the type-comments approach to typing so I'd be -0 on pytest itself starting to adopt mypy annotations until we can stop supporting python 2
• all this said, I usually don't bother annotating my tests 🤷‍♂️

[pior]

At work, we have more and more fully typed code-bases, and we type our tests as well.

👍 for exposing the private types and typing the public api !

Also: typeshed doesn't accept third-party stubs anymore, they are moving to a decentralized solution with the PEP-561.
While also discussing a third option: python/typeshed#2491

To add some context, here is an interesting stub project: https://github.com/dropbox/sqlalchemy-stubs

[Zac-HD]

Checklist:

• Create a stub file src/pytest.pyi for the public interface
• Create a src/py.typed file (per PEP 561) to indicate that the interface is type-checkable
• Check that this does not break everything by dumping the marker file into the root site-packages directory when installed.
• Add package_data={"": ['pytest.pyi', '__init__.pyi']}, to the metadata in setup.py
• Create a new public module pytest.types which exports all and only the internal types needed for type hinting.
• Clearly document that pytest.types is not guaranteed stable between minor versions of Pytest, so we don't get locked into a compatible but terrible early version.

[RonnyPfannschmidt]

that pytest.type thing can possibly get us into deep trouble - i i wonder how to sort that out

[CaselIT]

Just my 2 cents.
I think a pytest.fixture_types module to expose the private types as proposed before would be enough.