find local timezones as pytz.timezone objects

local_timezones.py

#!/usr/bin/env python
import os
import time
from datetime import timedelta
from hashlib import sha512

import pytz  # pip install pytz

def filehash(path):
    with open(path, 'rb') as file:
        return sha512(file.read()).hexdigest()

def local_timezones_from_etc_localtime():
    """
    http://stackoverflow.com/a/7841417
    """
    tzfile_digest = filehash('/etc/localtime')

    topdir = "/usr/share/zoneinfo/"
    for pathdir, dirs, files in os.walk(topdir):
        for filename in files:
            path = os.path.join(pathdir, filename)
            if filehash(path) == tzfile_digest:
                tzname = path[len(topdir):]
                try:
                    yield pytz.timezone(tzname)
                except pytz.UnknownTimeZoneError:
                    pass

def local_timezones_from_current_tzname_offset():
    """
    http://stackoverflow.com/a/8328904
    """
    if time.daylight and time.localtime().tm_isdst > 0:
        local_time_offset = time.altzone
        localtzname = time.tzname[1]
    else:
        local_time_offset = time.timezone
        localtzname = time.tzname[0]

    local_offset = timedelta(seconds=-local_time_offset)

    for name in pytz.all_timezones:
        timezone = pytz.timezone(name)
        if not hasattr(timezone, '_tzinfos'):
            continue  #skip, if some timezone doesn't have info
        # go thru tzinfo and see if short name like EDT and offset matches
        for (utcoffset, daylight, tzname), _ in timezone._tzinfos.items():
            if utcoffset == local_offset and tzname == localtzname:
                yield timezone


if __name__ == '__main__':
    print({tz.zone: tz for tz in local_timezones_from_etc_localtime()})
    print({tz.zone: tz for tz in local_timezones_from_current_tzname_offset()})