Python Dates

Python Dates: datetime, timedelta, and Formatting

Python's built-in datetime module handles calendar dates, clock times, timestamps, and duration math. Always prefer timezone-aware datetime objects (datetime.now(timezone.utc)) for servers, logs, and APIs so daylight saving changes never corrupt timestamps.

You can format dates into readable strings with strftime() and parse incoming strings back into datetime objects with strptime().

Creating, Formatting, and Shifting Dates

timedelta represents a duration (days, hours, minutes) that you add to or subtract from any date or datetime.

from datetime import datetime, timedelta, timezone

now_utc = datetime.now(timezone.utc)
expires_at = now_utc + timedelta(days=7)

formatted = now_utc.strftime("%Y-%m-%d %H:%M UTC")
parsed = datetime.strptime("2026-11-12", "%Y-%m-%d")

print(formatted, expires_at.date(), parsed.year)

For ISO 8601 strings like "2026-11-12T10:30:00Z", datetime.fromisoformat() in Python 3.11+ parses them directly without format codes.

Handling Named Timezones with zoneinfo

Since Python 3.9, the standard library zoneinfo.ZoneInfo converts UTC timestamps into regional timezones like "America/New_York" or "Asia/Dhaka" using IANA rules.

Common Mistakes to Avoid

• Mixing naive and timezone-aware datetimes: Subtracting a naive datetime.now() from a UTC-aware datetime raises TypeError.
• Using datetime.utcnow() in Python 3.12+: utcnow() is deprecated because it returns a naive object; call datetime.now(timezone.utc) instead.
• Confusing %m and %M: %m is month (01–12), while %M is minute (00–59).

Frequently Asked Questions

What is the difference between strftime and strptime?

strftime ("string format time") turns a datetime into a formatted string. strptime ("string parse time") turns a text string into a datetime object.

How do I calculate the number of days between two dates?

Subtract one date or datetime from the other to get a timedelta, then read its .days attribute.

How should I store timestamps in a database or JSON?

Store and serialize timestamps in UTC using ISO 8601 format (dt.isoformat()), and convert to the user's local timezone only at display time.