[case testAccessingGenericNonDataDescriptor]

from typing import TypeVar, Type, Generic

T = TypeVar('T')

V = TypeVar('V')

class D(Generic[T, V]):

def __init__(self, value: V) -> None:

self.value = value

def __get__(self, instance: T, owner: Type[T]) -> V:

return self.value

class A:

f = D(10) # type: D[A, int]

g = D('10') # type: D[A, str]

a = A() # type: A

reveal_type(a.f) # E: Revealed type is 'builtins.int*'

reveal_type(a.g) # E: Revealed type is 'builtins.str*'

[case testSettingGenericDataDescriptor]

from typing import TypeVar, Type, Generic

T = TypeVar('T')

V = TypeVar('V')

class D(Generic[T, V]):

def __init__(self, value: V) -> None:

self.value = value

def __get__(self, instance: T, owner: Type[T]) -> V:

return self.value

def __set__(self, instance: T, value: V) -> None:

pass

class A:

f = D(10) # type: D[A, int]

g = D('10') # type: D[A, str]

a = A() # type: A

a.f = 1

a.f = '' # E: Incompatible types in assignment (expression has type "str", variable has type "int")

a.g = ''

a.g = 1 # E: Incompatible types in assignment (expression has type "int", variable has type "str")