Dates & Time

Why this matters

Naive datetime objects (no tzinfo) are the root cause of daylight-saving bugs and off-by-one-day reports in every analytics stack. Since Python 3.9, zoneinfo replaces pytz; datetime.now(tz=...) should always be timezone-aware in production.

Common pitfalls

• Comparing naive and aware datetimes — raises TypeError; standardize on UTC-aware at boundaries.
• Using datetime.utcnow() — returns naive; prefer datetime.now(timezone.utc) for explicit UTC.
• Doing calendar math with timedelta(days=30) for "one month" — use dateutil.relativedelta for real months.