Python ведущий подчеркивание _variables

Я не уверен, что не так с numpy; но с csv он отлично работает:

>>> import time
>>> import csv
>>> with open('t.txt') as f:
...    r = csv.reader(f)
...    w = [[time.strptime(i[0], '%Y-%m-%d %H:%M:%S.%f')]+i[1:] for i in r]
...
>>> w
[[time.struct_time(tm_year=2013, tm_mon=12, tm_mday=11, tm_hour=23, tm_min=0, tm_sec=27, tm_wday=2, tm_yday=345, tm_isdst=-1), '$PAMWV', '291', 'R', '005.8', 'M', 'A*36'], [time.struct_time(tm_year=2013, tm_mon=12, tm_mday=11, tm_hour=23, tm_min=0, tm_sec=28, tm_wday=2, tm_yday=345, tm_isdst=-1), '$PAMWV', '284', 'R', '005.5', 'M', 'A*3F'], [time.struct_time(tm_year=2013, tm_mon=12, tm_mday=11, tm_hour=23, tm_min=0, tm_sec=29, tm_wday=2, tm_yday=345, tm_isdst=-1), '$PAMWV', '273', 'R', '004.0', 'M', 'A*33'], [time.struct_time(tm_year=2013, tm_mon=12, tm_mday=11, tm_hour=23, tm_min=0, tm_sec=30, tm_wday=2, tm_yday=345, tm_isdst=-1), '$PAMWV', '007', 'R', '004.9', 'M', 'A*3B']]