Remove an item by value, consulting the keyfunc for the key.

def remove(self, value, _sa_initiator=None):
        """Remove an item by value, consulting the keyfunc for the key."""

        key = self.keyfunc(value)
        # Let self[key] raise if key is not in this collection
        # testlib.pragma exempt:__ne__
        if not self.__contains__(key) or value not in self[key]:
            raise sa_exc.InvalidRequestError(
                "Can not remove '%s': collection holds '%s' for key '%s'. "
                "Possible cause: is the MappedCollection key function "
                "based on mutable properties or properties that only obtain "
                "values after flush?" %
                (value, self[key], key))
        self.__getitem__(key, _sa_initiator).remove(value)