invert dictionary python

inv_map = {v: k for k, v in my_map.items()}

def inverse_dict(my_dict):
    """
    the func get a dictinary and reverse it, the keys become values and the values become keys.
    :param my_dict: the dictinary that need to be reversed.
    :return: a VERY pretty dictionary.
    """
    result_dict = {}
    for key, value in my_dict.items():
        if not value in result_dict.keys():
            result_dict[value] = []
        result_dict[value].append(key)
    return result_dict, print(result_dict)