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ParamSpec parameters don't match __init__ parameters of class #12986
Description
from functools import partial
from typing import Callable, Generic, ParamSpec
P = ParamSpec('P')
class custom_vjp(Generic[P]):
def __init__(self,
fun: Callable[P, None],
x: int = 0):
super().__init__()
self.fun = fun
def __call__(self, *args: P.args, **kwargs: P.kwargs) -> None:
return self.fun(*args, **kwargs)
@partial(custom_vjp, x=1) # error: Argument 1 to "partial" has incompatible type "Type[custom_vjp[Any]]"; expected "Callable[..., custom_vjp[P]]"
def f() -> None:
pass
Activity
kstauffer commentedon Jun 20, 2022
You get the same error without the decorator (delete the
@character and the last two lines entirely). The error is at the instantiation of thepartialobject.The problem is the use of an unbound type in a way that mypy cannot handle. Where the error message says "Any" is misleading; the internal state of mypy still has "P" unbound. Notice that mypy is happy if you explicitly annotate or cast with the same dubious type mypy already claims to think it has:
That's proof that the mypy error message is not really telling you what's gone wrong inside mypy.
I am working on a plugin to properly handle functools.partial and partialmethod. I'll be sure this handle this test case.
NeilGirdhar commentedon Jun 21, 2022
Awesome!! Really looking forward to your plugin. And thank you for diagnosing the error and providing a workaround.
ilevkivskyi commentedon Aug 16, 2023
The original example works on master, likely fixed by #15837