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Using generic self in a generic class #3363
Description
The recommended method for writing a factory method is to type the cls argument as Type[T] (http://mypy.readthedocs.io/en/latest/generics.html#generic-methods-and-generic-self). However, this doesn't seem to be able to handle the case where the factory class itself is generic.
In the example below, if we just specify bound=FactoryBase on the _FactoryBase typevar, mypy gives error: Argument 1 to "make" of "FactoryBase" has incompatible type "int"; expected "T".
from typing import (
Any,
Generic,
TypeVar,
Type,
)
T = TypeVar('T')
_FactoryBase = TypeVar('_FactoryBase', ???)
class FactoryBase(Generic[T]):
def __init__(self, obj):
# type: (T) -> None
pass
@classmethod
def make(cls, obj):
# type: (Type[_FactoryBase], T) -> _FactoryBase
return cls(obj)
class Factory(FactoryBase[int]):
pass
Factory.make(2)
Activity
ilevkivskyi commentedon May 16, 2017
It looks like this is a duplicate of #2354 (although I am not 100% sure).
ilevkivskyi commentedon May 16, 2017
Maybe it makes to copy this example (i.e. with
@classmethod) to the original issue an close this one?ilevkivskyi commentedon Jun 11, 2019
FWIW the original example (with
bound=FactoryBase) works correctly on master.