def invert_dict(dictio):

    """ Invert dictionary whose values are lists and are not
        unique.

        Args:
            dictio (dictionary): the dictionary to invert.

        Returns:
            inv_dict (dictionary): a dictionary where the old values are 
                now keys and the old keys are now in the 
                value lists.
    """

    inv_dict={}

    for k, v in dictio.items():
        for g in v:
            if g not in inv_dict.keys():
                inv_dict[g] =   []
            inv_dict[g].append(k)

    return inv_dict