calendar.timegm not always an inverse of time.gmtime

GitHub fields:

assignee = 'https://github.com/abalkin'
closed_at = None
created_at = <Date 2018-05-19.10:41:39.778>
labels = ['3.8', 'type-feature', 'library']
title = 'calendar.timegm not always an inverse of time.gmtime'
updated_at = <Date 2018-05-20.19:25:09.271>
user = 'https://github.com/grimreaper'

bugs.python.org fields:

activity = <Date 2018-05-20.19:25:09.271>
actor = 'belopolsky'
assignee = 'belopolsky'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2018-05-19.10:41:39.778>
creator = 'eitan.adler'
dependencies = []
files = []
hgrepos = []
issue_num = 33579
keywords = []
message_count = 8.0
messages = ['317111', '317133', '317145', '317183', '317190', '317191', '317197', '317199']
nosy_count = 4.0
nosy_names = ['tim.peters', 'belopolsky', 'martin.panter', 'eitan.adler']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue33579'
versions = ['Python 3.8']