mvanveen / times

Times and time zones in Python with a focus on best practices.

Times

Times is a small, minimalistic, Python library for dealing with time conversions to and from timezones, for once and for all.

It is designed to be simple and clear, but also opinionated about good and bad practices.

Armin Ronacher wrote about timezone best practices in his blog post Dealing with Timezones in Python. The tl;dr summary is that everything sucks about our mechanisms to represent absolute moments in time, but the least worst one of all is UTC.

Rationale

Python's datetime library and the pytz library are powerful, but because they don't prescribe a standard practice of working with dates, everybody is free to pick his or her own way.

times tries to make working with times and timezones a little less of a clusterfuck and hopefully set a standard of some sort.

It still uses datetime and pytz under the covers, but as long as you never use any timezone related stuff outside times, you should be safe.

Accepting time

Never work with local times. Whenever you must accept local time input (e.g. from a user), convert it to universal time immediately:

>>> times.to_universal(local_time, 'Europe/Amsterdam')
datetime.datetime(2012, 2, 1, 10, 31, 45, 781262)

You can approach the conversion from the other side, too, as to_universal is conveniently aliased to from_local:

>>> times.from_local(local_time, 'Europe/Amsterdam')
datetime.datetime(2012, 2, 1, 10, 31, 45, 781262)

The second argument can be a pytz.timezone instance, or a timezone string.

If the local_time variable already holds timezone info, you must leave out the source timezone from the call.

To enforce best practices, times will never implicitly convert times for you, even if that would technically be possible.

When you want to record the current time, you can use this convenience method:

>>> import times
>>> print times.now()
datetime.datetime(2012, 2, 1, 11, 51, 27, 621491)

Presenting times

To present times to the end user of your software, you should format your absolute time to your user's local timezone.

>>> import times
>>> now = times.now()
>>> print times.format(now, 'CET')
2012-02-01 21:32:10+0100

As with the to_universal function, the second argument may be either a timezone instance or a timezone string.

Note: It is possible to convert universal times to local times, using to_local (or the alias from_universal). However, you probably shouldn't do it, unless you want to strftime() the resulting local date multiple times. In any other case, you are advised to use times.format() directly instead.