pandas - python: slice according to an irregular pattern -

below, can find excerpt pandas timeseries. slice rows set apart white space. there recurring pattern, i.e. 21 times value x, 4 different values abcd, 21 times value y, 4 different values efgh, 21 times value z etc. in case, i'm interested in obtaining bcdy, fghz , on.

the problem pattern interrupted due missing data.

any ideas? thanks.

2014-01-20 00:00:00    197021 2014-01-20 00:01:00    197021 2014-01-20 00:02:00    197021 2014-01-20 00:03:00    197021 2014-01-20 00:04:00    197021 2014-01-20 00:05:00    197021 2014-01-20 00:06:00    197021 2014-01-20 00:07:00    197021 2014-01-20 00:08:00    197021 2014-01-20 00:09:00    197021 2014-01-20 00:10:00    197021 2014-01-20 00:11:00    197021 2014-01-20 00:12:00    197021 2014-01-20 00:13:00    197021 2014-01-20 00:14:00    197021 2014-01-20 00:15:00    197021 2014-01-20 00:16:00    196836  2014-01-20 00:17:00    196865 2014-01-20 00:18:00    196787 2014-01-20 00:19:00    196915 2014-01-20 00:20:00    196902  2014-01-20 00:21:00    196902 2014-01-20 00:22:00    196902 2014-01-20 00:23:00    196902 2014-01-20 00:24:00    196902 2014-01-20 00:25:00    196902 2014-01-20 00:26:00    196902 2014-01-20 00:27:00    196902 2014-01-20 00:28:00    196902 2014-01-20 00:29:00    196902 

can not iterate though lines, adding current group's list of lines, , on empty line, change list you're appending too? assumes missing data not return empty string on not creating new line.

x = 1 groups = { 1 : [], 2 : [], 3 : [] } line in file_obj.readlines():     if line:       groups[x].append(line)     else:        x += 1        if x > 3:           x = 0