Self type support

[qgallouedec]

It would be nice to support the Self type in the future. Is there a plan in this direction?

PEP 673

Code example

foo.py:

from typing_extensions import Self

class A:
    def func(self) -> Self:
        return self

$ pytype foo.py
[...]
File "/Users/quentingallouedec/foo.py", line 1, in <module>: typing_extensions.Self not supported yet [not-supported-yet]

[rchen152]

Generally, we add support for new typing features a few months after adding support for the corresponding Python version. Since Self is in 3.11, which we haven't started seriously looking at yet, it'll probably be sometime next year before we support it.

[eltoder]

Hi @rchen152! What is the status of Self type now? It looks like you added support for even some complex cases, but when I try the example from OP with pytype 2023.06.16, I still get

File "/home/eltoder/dev/scratch/self_type.py", line 1, in <module>: typing.Self not supported yet [not-supported-yet]
File "/home/eltoder/dev/scratch/self_type.py", line 5, in func: bad return type [bad-return-type]
           Expected: Self
  Actually returned: A

[rchen152]

I added some support specifically for Self type in .pyi (stub) files, to help with updating the typeshed version that pytype uses. From a pytype user perspective, what I'm adding now probably isn't particularly useful, since it doesn't allow you to use Self in .py source files.

[eltoder]

Got it, thanks!

[rchen152]

Next week's pytype release will have Self support.

[tboddyspargo]

@rchen152 - I'm getting Cannot use 'typing.Self' outside of a class in with a situation approximately like this in python 3.11:

class A:
    def a(self, **kwargs) -> "Self":
        return self.__class__(**(self.__dict__ | kwargs))

class B(A):
    @overrides.override
    def a(self, **kwargs) -> "Self":
        self.super().a(**(dict(option="default") | kwargs))

Is this considered an inappropriate use of typing.Self, or does this indicate a gap in pytype's support for its use in the annotations of methods?