Demonstrates pytz violates python spec

pytz_madness.py

# Please read https://blog.ganssle.io/tag/pytz.html

import datetime


# The Good

try:
    import zoneinfo
except ImportError:
    from backports import zoneinfo

berlin = zoneinfo.ZoneInfo("Europe/Berlin")

dt1 = datetime.datetime(2021, 10, 31, 2, tzinfo=berlin, fold=0)
dt2 = datetime.datetime(2021, 10, 31, 2, tzinfo=berlin, fold=1)

print(dt1.isoformat())
print(dt2.isoformat())
print(dt2 - dt1)  # -> 0:00:00 according python specs


# The Ugly

from pytz import timezone
berlin = timezone('Europe/Berlin')

dt1 = berlin.localize(datetime.datetime(2021, 10, 31, 2), is_dst=True)
dt2 = berlin.localize(datetime.datetime(2021, 10, 31, 2), is_dst=False)

print(dt1.isoformat())
print(dt2.isoformat())
print(dt2 - dt1)  # -> 1:00:00 in violation of python specs

See also https://pytz-deprecation-shim.readthedocs.io/en/latest/