How do you convert a naive datetime to DST-aware datetime in Python?

Question

I\'m currently working on the backend for a calendaring system that returns naive Python datetimes. The way the front end works is the user creates various calendar events,

Answer 1

with Python 3.9's zoneinfo:

from datetime import datetime
from zoneinfo import ZoneInfo   

naive_datetime = datetime(2011, 10, 26, 12, 0, 0)

user_tz_preference = ZoneInfo('US/Pacific')
user_datetime = naive_datetime.replace(tzinfo=user_tz_preference) # safe with zoneinfo
utc_datetime = user_datetime.astimezone(ZoneInfo('UTC'))

print(repr(user_datetime))
# datetime.datetime(2011, 10, 26, 12, 0, tzinfo=zoneinfo.ZoneInfo(key='US/Pacific'))
print(user_datetime.isoformat())
# 2011-10-26T12:00:00-07:00
print(utc_datetime.isoformat())
# 2011-10-26T19:00:00+00:00

docs

Answer 2

Pytz's localize function can do this: http://pytz.sourceforge.net/#localized-times-and-date-arithmetic

from datetime import datetime
import pytz    

tz = pytz.timezone('US/Pacific')
naive_dt = datetime(2020, 10, 5, 15, 0, 0) 
utc_dt = tz.localize(naive_dt, is_dst=None).astimezone(pytz.utc)
# -> 2020-10-05 22:00:00+00:00