Python: strftime() UTC Offset Not working as Expected in Windows

Question

Every time I use:

time.strftime("%z")

I get:

Eastern Daylight Time

However, I would like the UTC offset in the form +HHMM or -HHMM. I have even tried:

time.strftime("%Z")

Which still yields:

Eastern Daylight Time

I have read several other posts related to strftime() and %z always seems to return the UTC offset in the proper +HHMM or -HHMM format. How do I get strftime() to output in the +HHMM or -HHMM format for python 3.3?

Edit: I'm running Windows 7

Answer 1

In 2.x, if you look at the docs for time.strftime, they don't even mention %z. It's not guaranteed to exist at all, much less to be consistent across platforms. In fact, as footnote 1 implies, it's left up to the C strftime function. In 3.x, on the other hand, they do mention %z, and the footnote that explains that it doesn't work the way you'd expect is not easy to see; that's an open bug.

However, in 2.6+ (including all 3.x versions), datetime.strftime is guaranteed to support %z as "UTC offset in the form +HHMM or -HHMM (empty string if the the object is naive)." So, that makes for a pretty easy workaround: use datetime instead of time. Exactly how to change things depends on what exactly you're trying to do — using Python-dateutil tz then datetime.now(tz.tzlocal()).strftime('%z') is the way to get just the local timezone formatted as a GMT offset, but if you're trying to format a complete time the details will be a little different.

If you look at the source, time.strftime basically just checks the format string for valid-for-the-platform specifiers and calls the native strftime function, while datetime.strftime has a bunch of special handling for different specifiers, including %z; in particular, it will replace the %z with a formatted version of utcoffset before passing things on to strftime. The code has changed a few times since 2.7, and even been radically reorganized once, but the same difference is basically there even in the pre-3.5 trunk.

Answer 2

For a proper solution, see abarnert’s answer below.

---

You can use time.altzone which returns a negative offset in seconds. For example, I’m on CEST at the moment (UTC+2), so I get this:

>>> time.altzone
-7200

And to put it in your desired format:

>>> '{}{:0>2}{:0>2}'.format('-' if time.altzone > 0 else '+', abs(time.altzone) // 3600, abs(time.altzone // 60) % 60)
'+0200'

---

As abarnert mentioned in the comments, time.altzone gives the offset when DST is active while time.timezone does for when DST is not active. To figure out which to use, you can do what J.F. Sebastian suggested in his answer to a different question. So you can get the correct offset like this:

time.altzone if time.daylight and time.localtime().tm_isdst > 0 else time.timezone

As also suggested by him, you can use the following in Python 3 to get the desired format using datetime.timezone:

>>> datetime.now(timezone.utc).astimezone().strftime('%z')
'+0200'