Attributes of property objects can't be accessed

[JukkaL]

Originally reported by @ilevkivskyi in #220 (comment):

Another thing that doesn't work came in #6045: accessing attributes of a property object in the class body (for example fset, fget etc). This can be probably partially solved by some special casing in checkmember.py.

[Pathfinder216]

If I understand this correctly, I just ran into an issue related to this. I get a mypy error when overriding a property in a subclass.

class Base:
    @property
    def foo(self):
        return self._foo

    @foo.setter
    def foo(self, val):
        self._foo = val


class Sub(Base):
    @Base.foo.setter  # mypy error
    def foo(self, val):
        self._foo = val + 1

The error I get:

foo.py:12: error: overloaded function has no attribute "setter"

[harahu]

I encountered this issue when trying to use a Result-like wrapper type, and I want to interact with the property of a wrapped object.

The following program runs fine, but generates a mypy error:
error: "Callable[[Person], str]" has no attribute "fget" [attr-defined]

https://gist.github.com/mypy-play/12b11a6d77c3e70413514c4666015aa2

from dataclasses import dataclass

from result import Ok


@dataclass
class Person:
    _name: str

    @property
    def name(self) -> str:
        return self._name.title()


person_result = Ok(Person(_name="john doe"))

name_result = person_result.map(Person.name.fget)

name = name_result.value

print(name)

I could avoid the false positive by using lambda p: p.name, in place of Person.name.fget, but I prefer the latter because it clearly documents what I expect the to reside within the wrapper, which I think helps readability.

P.S: Maybe of interest to @sobolevn given the functional patterns at play? 😉

[eltoder]

A minimal example for clarification:

class C:
    @property
    def p(self) -> int:
        return 1

C.p.fget
C.p.fset
C.p.fdel

$ mypy --strict t.py
t.py:6: error: "Callable[[C], int]" has no attribute "fget"  [attr-defined]
t.py:7: error: "Callable[[C], int]" has no attribute "fset"  [attr-defined]
t.py:8: error: "Callable[[C], int]" has no attribute "fdel"  [attr-defined]
Found 3 errors in 1 file (checked 1 source file)

mypy believes that C.p is Callable[[C], int] rather than a property wrapping that function and generates false positives on access.

[josmithua]

Still an issue a few years later. Can we get this fixed?