def reverse_dict_old(dikt):
    """
    takes a dict and return a new dict with old values as key and old keys as values (in a list)

    example

    _reverse_dict({'AB04a':'b', 'AB04b': 'b', 'AB04c':'b', 'CC04x': 'c'})

    will return
        {'b': ['AB04a', 'AB04b', 'AB04c'], 'c': 'CC04x'}
    """

    new_dikt = {}
    for k, v in dikt.items():
        if v in new_dikt:
            new_dikt[v].append(k)
        else:
            new_dikt[v] = [k]
    return new_dikt