I have two classes inheriting from dict, like this:
class A(dict):
class B(A):
This all works fine - the two classes use the inherited dict functionality and do other required stuff. However, I also want to use type-hinting. The first should reduce the range of the Dict generic and the second should reduce it further. For example, I'd like to write something like:
class A(Dict[str, Any]):
class B(A[str, int]):
This works fine for A but not for B (that code is not syntactically correct, of course).
Class B isn't a sub-type of A (since it can't handle anything other than int) and that's fine but I do need it to inherit. Can I get mypy to understand the correct type of B and still inherit from A?
The only solution I can see at present is to re-implement all the inherited methods from A but that would be a lot of runtime boiler-plate just to declare the correct typing.
So a little more thought and I think it's easy. I just need to move the shared functionality out of A and into a new generic which inherits from Dict. Simple:
from typing import Generic, TypeVar, Dict, Any
KT = TypeVar('KT')
VT = TypeVar('VT')
class GenericA(Dict[KT, VT]):
def my_method(self):
print(list(self.values()))
A = GenericA[str, Any]
class B(GenericA[str, int]):
def more_methods(self):
print(list(self.keys()))
a = A({"a" : "blob", "b" : "blib"})
a.my_method()
b = B({"a" : 1, "b" : 2})
b.my_method()
b.more_methods()