python dictionary with restricted key type, given at compile time

typeddict.py

# -*- coding: utf-8 -*-
class TypedDict(dict):
    """Dictionary with keys restricted to a specific type, given at creation time"""

    def __init__(self, key_type):
        print("initializing with", key_type)
        self.key_type = key_type

    def __getstate__(self):
        return self.key_type, dict(self)

    def __setstate__(self, state):
        self.key_type, data = state
        self.update(data)

    def __reduce__(self):
        # need custom reduce to bypass dict's special deserialization protocol
        return TypedDict, (self.key_type,), self.__getstate__()

    def __setitem__(self, key, value):
        if isinstance(key, self.key_type):
            return super(TypedDict, self).__setitem__(key, value)
        raise KeyError(
            "dictionary accepts only keys of type {} but given {}".format(self.key_type.__name__, type(key).__name__))