Force pyright not to evaluate __init__ when __new__ returns an object that is not a subtype

[maximlt]

pyright reports error: Expected 0 positional arguments (reportCallIssue) when checking this snippet.

class Base:
    def __init__(self, **params):
        pass

class FunctionBase(Base):

    def __new__(cls, *args, **kwargs):
        inst = Base.__new__(cls)
        result = inst.__call__(*args, **kwargs)
        return result

    def __call__(self, *args, **kwargs):
        raise NotImplementedError

class SomeFunction(FunctionBase):
    def __call__(self, *args, **kwargs):
        return 1

SomeFunction('test')

The typing spec includes this:

For purposes of this test, an explicit return type of Any (or a union containing Any) should be treated as a type that is not an instance of the class being constructed.

So I annotated the return type of __new__ with Any but it didn't change anything.

Instead, I added a dummy __init__ definition to FunctionBase that accepts args and kwargs, which cleared the error.

class FunctionBase(Base):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

Is this the only solution available? What should pyright do when __new__ is annotated with Any as its return type?

[erictraut]

Yes, you're correct. Pyright isn't following the typing spec here. The spec conformance test tests for a union that contains Any but doesn't check for an Any by itself. (I wrote this conformance test, so the omission was my fault.) That explains why this bug wasn't caught earlier. I also didn't have this case covered in the pyright unit tests.

I've created a separate bug report to track the issue.

This issue will be fixed in the next release of pyright. I've also updated the unit tests to cover this case.

[maximlt]

Wonderful, thanks!