def merge_two_dicts(first_dict, second_dict):
    """ Merges two python dicts by making a copy of first then updating with second.
        Returns a copy. """

    return_dict = first_dict.copy()  # start with x's keys and values
    return_dict.update(
        second_dict
    )  # modifies z with y's keys and values & returns None
    return return_dict