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Decorator on method in derived class #1441
Description
A decorator that changes the signature of a function is rejected if the old signature isn't consistent with the superclass. E.g.:
def convert_to_bool(f):
# type: (Callable[..., int]) -> Callable[..., bool]
def wrapper(*n, **kw):
i = f(*n, **kw)
return i < 10
return wrapper
class Base(object):
def f(self):
# type: () -> bool
return True
class Derived(Base):
@convert_to_bool
def f(self):
# type: () -> int
return 20
The interesting point here is that the base class doesn't use the decorator while the child does. Our particular issue is in code that uses contextlib.contextmanager, but I think we can work around it by adding the decorator to the base class.
Activity
drewhaven commentedon Apr 25, 2016
Actually, that work-around doesn't currently work. Adding the decorator to
Base.fstill gives the error onDerived.f:Signature of "f" incompatible with supertype "Base"gvanrossum commentedon Apr 26, 2016
Looking at the code a bit, it looks like check_method_override(), which is supposed to check whether Derived.f is compatible with Base.f, is called with the undecorated function. I'm guessing the decorator is stripped off somewhere a little earlier -- in fact, it seems the cuprit here is visit_decorator() that just calls e.func.accept().
gvanrossum commentedon Aug 1, 2017
We really should fix this one!
JukkaL commentedon Aug 8, 2017
More examples in #2469.
Fix type checking decorated method overrides
[-]Decorator on function in derived class[/-][+]Decorator on method in derived class[/+]Fix type checking decorated method overrides (#3918)