Given two dicts return another two dicts that contain only the differences between the original dicts

dict_diff.py

import unittest


def dict_diff(a, b):
    if a == b:
        return ({}, {})

    diff = ({}, {})
    keys = set(a.keys() + b.keys())
    for k in keys:
        if k in a and k not in b:
            diff[0][k] = a[k]
            continue

        if k not in a and k in b:
            diff[1][k] = b[k]
            continue

        if a[k] != b[k]:
            if type(a[k]) == type(b[k]) == dict:
                diff[0][k], diff[1][k] = dict_diff(a[k], b[k])

                if not diff[0][k]:
                    del diff[0][k]

                if not diff[1][k]:
                    del diff[1][k]
            else:
                diff[0][k] = a[k]
                diff[1][k] = b[k]

    return (diff[0], diff[1])


class DictDiffTest(unittest.TestCase):
    def test_1d_same(self):
        a = {'a': 'a', 'b': 'b', 'c': 'c'}
        b = {'a': 'a', 'b': 'b', 'c': 'c'}
        self.assertEqual(
            dict_diff(a, b),
            ({}, {})
        )

    def test_1d_new_keys(self):
        a = {'a': 'a', 'b': 'b'}
        b = {'a': 'a', 'b': 'b', 'c': 'c'}
        self.assertEqual(
            dict_diff(a, b),
            ({}, {'c': 'c'})
        )

    def test_1d_different_values(self):
        a = {'a': 'a', 'b': 'b', 'c': 'c'}
        b = {'a': 'a', 'b': 'bb', 'c': 'cc'}
        self.assertEqual(
            dict_diff(a, b),
            ({'b': 'b', 'c': 'c'}, {'b': 'bb', 'c': 'cc'})
        )

    def test_1d_different_keys(self):
        a = {'a': 'a', 'b': 'b', 'c': 'c'}
        b = {'a': 'a', 'b': 'b', 'd': 'd'}
        self.assertEqual(
            dict_diff(a, b),
            ({'c': 'c'}, {'d': 'd'})
        )

    def test_1d_different_keys_n_values(self):
        a = {'a': 'a', 'b': 'b', 'c': 'c'}
        b = {'a': 'a', 'b': 'bb', 'd': 'd'}
        self.assertEqual(
            dict_diff(a, b),
            ({'b': 'b', 'c': 'c'}, {'b': 'bb', 'd': 'd'})
        )

    def test_2d_same(self):
        a = {'a': {'1': '1'}, 'b': {'2': '2', '3': '3'}}
        b = {'a': {'1': '1'}, 'b': {'2': '2', '3': '3'}}
        self.assertEqual(
            dict_diff(a, b),
            ({}, {})
        )

    def test_2d_new_keys(self):
        a = {'a': {'1': '1'}, 'b': {'2': '2'}}
        b = {'a': {'1': '1', '2': '2'}, 'b': {'2': '2'}, 'c': 1}
        self.assertEqual(
            dict_diff(a, b),
            ({}, {'a': {'2': '2'}, 'c': 1})
        )

    def test_2d_different_keys(self):
        a = {'a': {'1': '1'}, 'b': {'2': '2', '3': '3'}}
        b = {'a': {'1': '1'}, 'b': {'2': '2', '4': '4'}}
        self.assertEqual(
            dict_diff(a, b),
            ({'b': {'3': '3'}}, {'b': {'4': '4'}})
        )

    def test_2d_different_values(self):
        a = {'a': {}, 'b': {'2': '2', '3': '3'}}
        b = {'a': {'1': '1'}, 'b': {'2': '2', '3': '33'}}
        self.assertEqual(
            dict_diff(a, b),
            ({'b': {'3': '3'}},
             {'a': {'1': '1'}, 'b': {'3': '33'}})
        )

    def test_2d_different_values_n_keys(self):
        a = {'a': {'1': '1'}, 'b': {'2': '2', '3': '3', '4': '4'}}
        b = {'a': {'1': '11'}, 'b': {'2': '2', '3': '33', '5': '5'}}
        self.assertEqual(
            dict_diff(a, b),
            ({'a': {'1': '1'}, 'b': {'3': '3', '4': '4'}},
             {'a': {'1': '11'}, 'b': {'3': '33', '5': '5'}})
        )


if __name__ == '__main__':
    suite = unittest.TestLoader().loadTestsFromTestCase(DictDiffTest)
    unittest.TextTestRunner(verbosity=2, descriptions=False).run(suite)