def prepare_lists(listen_by_party_and_bundesland):
    """ This function quickly prepares the dictionary by including
    in each dataframe a column Sitz_Bundestag.

    Input:
    listen_by_party_and_bundesland (dict): contains for each Bundesland
        a dictionary containing parties with their lists
    
    Output:
    listen_by_party_and_bundesland (dict): same as input only that
        a column Sitz_Bundestag is added
    """

    for bundesland in listen_by_party_and_bundesland.keys():
        for partei in listen_by_party_and_bundesland[bundesland].keys():
            listen_by_party_and_bundesland[bundesland][partei]["Sitz_Bundestag"] = 0
    
    return listen_by_party_and_bundesland