updated - create and return a new Python dictionary by merging multiple dictionaries

updated.py

#!/usr/bin/env python
#
# Written in 2013. by Senko Rasic <[email protected]>
# This code is Public Domain. You may use it as you like.


__all__ = ['updated']


def updated(dct, *others):
    """Create and return a new dictionary by merging multiple dictionaries.

    Creates a copy of dictionary `dct` and updates it with items from the
    other dictionaries in the order they were specified. If items with the
    same key appear in multiple dictionaries, the value used in the last
    appearance is used for the resulting dict.

    The function doesn't modify any of the arguments in any way.

    Returns the newly created dictionary.

    """
    dct = dct.copy()
    for other in others:
        dct.update(other)
    return dct


if __name__ == '__main__':
    from unittest import TestCase, main

    class UpdatedTests(TestCase):
        def test_updated_single_argument_copies_dict(self):
            a = {'foo': 1}
            b = updated(a)
            a = {}
            self.assertEqual(b, {'foo': 1})

        def test_updated_multiple_arguments_merges_items(self):
            a = updated({'foo': 1}, {'bar': 2}, {'baz': 3})
            self.assertEqual(a, {'foo': 1, 'bar': 2, 'baz': 3})

        def test_updated_multiple_key_values_use_last_value(self):
            a = updated({'foo': 1}, {'foo': 2}, {'foo': 3})
            self.assertEqual(a, {'foo': 3})

    main()