import re
file_list = ['20150301',
'20150301100.tar.gz',
'20150302',
'20150302100.tar.gz',
'20150303',
'20150303100.tar.gz']
matchOB = [x for x in file_list if re.search(r"^\d+$", x)]
print(matchOB)
aW1wb3J0IHJlCgpmaWxlX2xpc3QgPSBbJzIwMTUwMzAxJywKICcyMDE1MDMwMTEwMC50YXIuZ3onLAogJzIwMTUwMzAyJywKICcyMDE1MDMwMjEwMC50YXIuZ3onLAogJzIwMTUwMzAzJywKICcyMDE1MDMwMzEwMC50YXIuZ3onXQptYXRjaE9CID0gW3ggZm9yIHggaW4gZmlsZV9saXN0IGlmIHJlLnNlYXJjaChyIl5cZCskIiwgeCldCnByaW50KG1hdGNoT0Ip