%z is listed as a supported directive in the python 3 documentation (https://docs.python.org/3.5/library/time.html#time.strftime), but it doesn't actually do anything:

>>> from time import strptime
>>> strptime('+0000', '%z') == strptime('+0200', '%z')
True

As far as I can tell, there aren't any footnotes saying that %z might not be supported on some platforms, like it was back in python 2.

In case it matters, I'm using python 3.5.3 on linux.