bidict/tests/test_subclasshook.py

# -*- coding: utf-8 -*-
# Copyright 2018 Joshua Bronson. All Rights Reserved.
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.

"""
Test that if foreign code provides a class that conforms to
BidirectionalMapping's interface, it is automatically a subclass.
"""

from bidict import BidirectionalMapping


class MyBidirectionalMapping(dict):
    """Dummy type implementing the BidirectionalMapping interface."""

    def __inverted__(self):
        for (key, val) in self.items():
            yield (val, key)

    @property
    def inv(self):
        """Like :attr:`bidict.bidict.inv`."""
        return MyBidirectionalMapping(self.__inverted__())


class OldStyleClass:  # pylint: disable=old-style-class,no-init
    """In Python 2 this is an old-style class (not derived from object)."""


def test_bidi_mapping_subclasshook():
    """Ensure issubclass(foo, BidirectionalMapping) works as expected."""
    assert issubclass(MyBidirectionalMapping, BidirectionalMapping)
    assert not issubclass(dict, BidirectionalMapping)
    # Make sure this works with old-style classes as expected.
    assert not issubclass(OldStyleClass, BidirectionalMapping)