Lessons · Python · a time that knows its timezone

A time that knows where it is

A naive datetime carries no timezone; an aware one does. Python refuses to subtract one from the other, because the answer would be a guess.

Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.

What it is for

A server in one zone, a user in another, an API returning UTC: mixing them is how appointments land an hour off and 'is it expired' checks fail at midnight.

How to think about it

Make everything aware and keep it in UTC inside the program: datetime.now(timezone.utc). Convert to a local zone only at the edge, when a person will read it.

Worked example

from datetime import datetime, timezone

The two names you need.

naive = datetime(2026, 1, 1)

No zone.

aware = datetime(2026, 1, 1, tzinfo=timezone.utc)

Knows it is UTC.

print(naive.tzinfo, aware.tzinfo)

None UTC.

now = datetime.now(timezone.utc)

Aware from the start.

print((now - aware).days >= 0)

True: aware minus aware works; naive minus aware would raise TypeError.

Your turn

The current moment, aware, in UTC.

now = datetime.now()

The trap

datetime.utcnow() returns a naive value that merely happens to be UTC. It is deprecated for that reason; use datetime.now(timezone.utc).

Practise a time that knows its timezone on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.