def reverse_dict(dict_):
    """reverse dictionary

    Example:
    >>> d = {'iso': ['a', 'b'], 'iso2': ['b']}
    >>> reverse_dict(d)
    {'a': ['iso'], 'b': ['iso', 'iso2']}
    """
    _ = {}
    for k, v in dict_.items():
        for vv in list(v):
            _.setdefault(vv, []).append(k)

    return _