Spielereien mit Zeitzonen

#! /usr/bin/env python3
# -*- coding: utf-8 -

import sys
import datetime
import pytz

# ----------------------------------------------------------------------
# Liefert 1, wenn für einen Zeitstempel "dt" (mit Zeitzonen-Infos)
# gerade Sommerzeit herrscht. Sonst 0.
def localizedTimestampHasDst(dt):
    return dt.timetuple()[8]


# ----------------------------------------------------------------------
# Liefert für einen Zeitstempel aus der Zeitzone "zn" den entsprechenden
# Wert in UTC.
def timestampFromTzToUtc(dt, zn):
    return pytz.timezone(zn).localize(dt).astimezone(pytz.timezone('UTC'))


# ----------------------------------------------------------------------
# Liefert für einen Zeitstempel in UTC den entsprechenden Wert in der
# Zeitzone "zn"
def timestampFromUtcToTz(dt, zn):
    return pytz.timezone('UTC').localize(dt).astimezone(pytz.timezone(zn))


# ----------------------------------------------------------------------
#
def timezones_std_dst():
    tzd = dict()
    for tzs in pytz.common_timezones:
        tz = pytz.timezone(tzs)
        std, dst = None, None
        for month in range(1, 13):
            dt = datetime.datetime(2023, month, 1, 12, 0, 0)
            dt_tz = timestampFromUtcToTz(dt, tzs)
            l_dt_ts = localizedTimestampHasDst(dt_tz)
            tzv = dt_tz.utcoffset().total_seconds()/60/60
            if std is None and l_dt_ts == 0:
                std = tzv
                stdn = dt_tz.tzname()
            if dst is None and l_dt_ts == 1:
                dst = tzv
                dstn = dt_tz.tzname()
            if dst is not None and std is not None:
                break
        if dst is None:
            dst = std
            dstn = stdn
        tzd.update({tz: { "std": std, "dst": dst, 
                          "stdn": stdn, "dstn": dstn } })
    return tzd


# ----------------------------------------------------------------------
#
def find_dst_std_date():
    for tz in ("Europe/Berlin", "Atlantic/Bermuda", "UTC", "Canada/Newfoundland", "Australia/Lord_Howe", "Europe/Dublin", "Africa/Casablanca"):
    #for tz in pytz.common_timezones:
        print("\n", tz)
        dt = dt2 = datetime.datetime(2023, 1, 1, 0, 0)

        for h in range(6*24*365):
            dtz = timestampFromUtcToTz(dt, tz)
            dt_is_dst = localizedTimestampHasDst(dtz)
            #dt2 += datetime.timedelta(hours=1)
            dt2 += datetime.timedelta(minutes=10)
            dt2z = timestampFromUtcToTz(dt2, tz)
            dt2_is_dst = localizedTimestampHasDst(dt2z)
            if dt_is_dst != dt2_is_dst:
                print(dt, dt_is_dst, dtz)
                print(dt2, dt2_is_dst, dt2z, flush=True)
            dt = dt2


# ----------------------------------------------------------------------
# Tests
if __name__ == "__main__":
    tzd = timezones_std_dst()
    for tz, sd in tzd.items():
        ss = str(tz).split("/", 1)
        if len(ss) > 1:
            continent, city = ss
        else:
            continent, city = ss[0], ""
        if (sd["dst"]-sd["std"]) not in (0, 1.0):
            print("%20s / %-25s | %6s = %6.2f | %6s = %6.2f - %3.1f !!!!"%(continent, city, sd["stdn"], sd["std"], sd["dstn"], sd["dst"], sd["dst"]-sd["std"]))
        else:
            print("%20s / %-25s | %6s = %6.2f | %6s = %6.2f - %3.1f"%(continent, city, sd["stdn"], sd["std"], sd["dstn"], sd["dst"], sd["dst"]-sd["std"]))

    find_dst_std_date()