Mypy: Property, classmethod and staticmethod aliases not supported

[serhiy-storchaka]

MyPy does not support property aliases. Example:

$ cat a.py 
class A:
    @property
    def f(self) -> int:
        return 1
    g = f

x: int = A().f
y: int = A().g
$ mypy a.py 
a.py:8: error: Incompatible types in assignment (expression has type "Callable[[], int]", variable has type "int")

[ilevkivskyi]

Thanks for reporting!

Yeah, unfortunately properties are known to be often problematic. They were implemented via some special-casing before a more general descriptor support was added.

[serhiy-storchaka]

The problem is not only with properties, but with static and class methods too.

$ cat b.py
class A:
    @classmethod
    def f(cls) -> int:
        return 1
    g = f

x: int = A().f()
y: int = A().g()
$ mypy b.py
b.py:8: error: Invalid self argument "A" to attribute function "g" with type "Callable[[Type[A]], int]"

$ cat c.py
class A:
    @staticmethod
    def f() -> int:
        return 1
    g = f

x: int = A().f()
y: int = A().g()
$ mypy c.py
c.py:8: error: Attribute function "g" with type "Callable[[], int]" does not accept self argument

[ilevkivskyi]

Hm, this is more serious than I though then, raising priority to high.

[ex-nerd]

And apparently with callable properties on a dataclass (though the same errors are returned for a class with callable properties, which do not receive a self passed in when they are called):

from typing import Callable
from dataclasses import dataclass

@dataclass
class Demo:
    call_this: Callable[[str], str]

def call(s: str) -> str:
    return s

demo = Demo(call_this=call)

demo.call_this("test")

When run through mypy, this gets:

demo.py:13: error: Invalid self argument "Demo" to attribute function "call_this" with type "Callable[[str], str]"
demo.py:13: error: Too many arguments