python 30 lines · 4 steps

Timezone-safe datetime handling in Python

Convert, anchor, and compare datetimes across zones by refusing naive values and using zoneinfo as the source of truth.

Explained by highlit
Intermediate timezones datetime normalization zoneinfo validation
1from datetime import datetime
2from zoneinfo import ZoneInfo
3 
4 
5def to_timezone(dt, tz_name):
6 target = ZoneInfo(tz_name)
7 if dt.tzinfo is None:
8 raise ValueError("naive datetimes are ambiguous; attach a tzinfo first")
9 return dt.astimezone(target)
10 
11 
12def parse_utc(iso_string):
13 dt = datetime.fromisoformat(iso_string)
14 if dt.tzinfo is None:
15 return dt.replace(tzinfo=ZoneInfo("UTC"))
16 return dt.astimezone(ZoneInfo("UTC"))
17 
18 
19def schedule_across_zones(iso_string, zones):
20 moment = parse_utc(iso_string)
21 return {
22 zone: to_timezone(moment, zone).strftime("%Y-%m-%d %H:%M %Z%z")
23 for zone in zones
24 }
25 
26 
27def local_business_hours(iso_string, tz_name, open_hour=9, close_hour=17):
28 local = to_timezone(parse_utc(iso_string), tz_name)
29 is_weekday = local.weekday() < 5
30 return is_weekday and open_hour <= local.hour < close_hour
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Rejecting naive datetimes early prevents silent, hard-to-trace timezone bugs downstream.
  2. 2Normalizing everything to UTC gives you one canonical anchor before converting to display zones.
  3. 3Python's zoneinfo handles DST correctly, so aware conversions stay accurate across dates.

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