Python Basics: Parsing Timestamps and Converting to UTC

Python’s standard-library datetime module parses timestamps, converts offsets, and calculates durations. These examples use Python 3.12 or newer on Linux. The saved scripts create no data files.

Parse a timestamp with an offset

Save as demo_datetime_1.py:

from datetime import datetime, timezone

meeting = datetime.fromisoformat("2026-10-11T09:30:00+09:00")
meeting_utc = meeting.astimezone(timezone.utc)
print(meeting.isoformat())
print(meeting_utc.isoformat())
print(meeting == meeting_utc)

Run:

python3 demo_datetime_1.py

Output:

2026-10-11T09:30:00+09:00
2026-10-11T00:30:00+00:00
True

The offset makes this an aware datetime. Both representations identify the same instant. astimezone() converts the clock time; replacing tzinfo would only relabel it.

Add time and measure a duration

Save as demo_datetime_2.py:

from datetime import datetime, timedelta

started = datetime.fromisoformat("2026-10-11T23:45:00+00:00")
finished = started + timedelta(minutes=90)
print(finished.isoformat())
print((finished - started).total_seconds())

Run:

python3 demo_datetime_2.py

Output:

2026-10-12T01:15:00+00:00
5400.0

timedelta crosses the date boundary automatically. Use total_seconds() for the full duration; .seconds contains only the seconds remaining after whole days.

Reject timestamps without an offset

Without an offset, fromisoformat() produces a naive datetime. Parsing does not assume UTC. Check that requirement explicitly:

Save as demo_datetime_3.py:

from datetime import datetime

for timestamp in ["2026-10-11T09:30:00", "not-a-date"]:
    try:
        parsed = datetime.fromisoformat(timestamp)
        if parsed.utcoffset() is None:
            raise ValueError("offset required")
    except ValueError:
        print("Expected a valid timestamp with an offset")

Run:

python3 demo_datetime_3.py

Output:

Expected a valid timestamp with an offset
Expected a valid timestamp with an offset

Fixed offsets do not describe regional daylight-saving rules. Use zoneinfo for named regions. For elapsed-time calculations across clock changes, convert both endpoints to UTC before subtracting.

Reference

Python datetime documentation

Acknowledgements

This post was created with assistance from AI.