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Modules & Packages

datetime Module

Working with dates, times, and time deltas

Interview: Common in interviews — timezone handling and date arithmetic are practical skills

Last Updated: June 12, 2026 • 9 min read

The datetime module provides classes for working with dates, times, and time intervals. It's one of the most used standard library modules, essential for logging, scheduling, data processing, and any time-sensitive application.

Core Classes

  • date: Year, month, day — date(2026, 6, 12)
  • time: Hour, minute, second, microsecond — time(14, 30, 0)
  • datetime: Combines date and time — datetime(2026, 6, 12, 14, 30)
  • timedelta: Duration between two dates/times — timedelta(days=7, hours=3)
  • timezone: Fixed UTC offset — timezone.utc or timezone(timedelta(hours=5))

Formatting and Parsing

  • strftime: Format datetime to string — dt.strftime("%Y-%m-%d %H:%M")
  • strptime: Parse string to datetime — datetime.strptime("2026-06-12", "%Y-%m-%d")
  • ISO format: dt.isoformat() — standard "2026-06-12T14:30:00" format
  • fromisoformat: datetime.fromisoformat("2026-06-12T14:30:00") — parse ISO strings (Python 3.7+)

Naive vs Aware Datetimes

A naive datetime has no timezone info; an aware datetime has timezone. NEVER compare naive and aware datetimes — it raises TypeError. For production code, always use timezone-aware datetimes (UTC internally, convert for display).

Use zoneinfo for Timezones

Python 3.9+ includes zoneinfo for IANA timezone support: from zoneinfo import ZoneInfo; tz = ZoneInfo("America/New_York"). No more external pytz dependency.

Use Cases

Logging with timestamps for debugging and auditing

Scheduling tasks and calculating deadlines with timedelta

Working with APIs that use ISO 8601 date formats

Timezone conversion for global applications

Age, duration, and business day calculations

Common Mistakes

Using naive datetimes in production — always use timezone-aware (UTC internally)

Comparing naive and aware datetimes — raises TypeError; make both aware or both naive

Using datetime.now() instead of datetime.now(timezone.utc) — ambiguous local time

Not knowing timedelta.total_seconds() — .seconds only gives seconds within the day

Formatting with wrong codes — %m is month (number), %M is minute; %Y is year, %y is 2-digit year