[pandas] monthly

monthly = ['2017-04-01', '2017-05-01', '2017-06-01', '2017-07-01',
           '2017-08-01', '2017-09-01', '2017-10-01', '2017-11-01',
           '2017-12-01', '2018-01-01', '2018-02-01', '2018-03-01',
           '2018-04-01', '2018-05-01', '2018-06-01', '2018-07-01',
           '2018-08-01', '2018-09-01', '2018-10-01']
prev_suffix = []
_flag = False
to_read = []
to_remove = []
kokaku_duration = cols['PARAMS']['KOKAKU_DAYS']
for m in monthly:
    n_acc_list = []
    # determine month suffix
    d_end = pd.to_datetime(m, format='%Y-%m-%d')
    d_begin = d_end - pd.DateOffset(days=int(kokaku_duration - 1))
    date_suffix = list(pd.date_range(start=d_begin, end=d_end, freq='D').strftime('%Y%m').drop_duplicates())
    for _suffix in date_suffix:
        if _flag:
            to_read = list(set(date_suffix) - set(prev_suffix))
            to_remove = list(set(date_suffix) ^ set(prev_suffix))
            to_remove = list(list(set(to_read) - set(to_remove)) + list(set(to_remove)-set(to_read)))
        else:
            to_read = date_suffix

    # update state
    prev_suffix = date_suffix
    _flag = True
    print(_suffix)
    print('to read: {}'.format(to_read))
    print('to delete: {}\n'.format(to_remove))