Demonstrate why pytz.timezone.normalize() may be useful after datetime.replace() in Python

demo_normalize_replace.py

"""Demonstrate why tz.normalize() may be useful after dt.replace()."""
from datetime import datetime
import pytz

# see Localized times and date arithmetic section in pytz docs
# http://pytz.sourceforge.net/#localized-times-and-date-arithmetic
eastern = pytz.timezone('US/Eastern')
dt = eastern.localize(datetime(2002, 10, 27, 7, 0, 0), is_dst=None)
unnormalized_dt = dt.replace(hour=0, minute=0, second=0)
print(unnormalized_dt.utcoffset())
# -> -1 day, 19:00:00
print(eastern.normalize(unnormalized_dt).utcoffset())
# -> -1 day, 20:00:00 #NOTE: different!!!