The datetime module only supports timezone offsets within 24 hours of UTC:

https://docs.python.org/3/library/datetime.html#datetime.tzinfo.utcoffset

This seems like an arbitrary restriction, and prevents the library from being used in arbitrary timezone translations. For various reasons, one might need to start a new day (perhaps to implement some business logic) during the regular day. Depending on when/where this is, the effective offset can easily be greater than 24 hours.

>>> import datetime
>>> import pytz

>>> dt = pytz.utc.localize(datetime.datetime.utcnow())
>>> dt
datetime.datetime(2015, 8, 31, 23, 30, 55, 590037, tzinfo=<UTC>)

>>> tz = pytz.timezone('Pacific/Auckland_Custom')
>>> dt.astimezone(tz)
datetime.datetime(2015, 9, 2, 4, 30, 55, 590037, tzinfo=<DstTzInfo 'Pacific/Auckland_Custom' NZST+1 day, 5:00:00 STD>)

>>> dt_local = datetime.datetime.now()
>>> tz.localize(dt_local)
.../python2.7/site-packages/pytz/tzinfo.py in localize(self, dt, is_dst)
    314 loc_dt = tzinfo.normalize(dt.replace(tzinfo=tzinfo))
    315 if loc_dt.replace(tzinfo=None) == dt:
--> 316 possible_loc_dt.add(loc_dt)
    317
    318 if len(possible_loc_dt) == 1:

ValueError: tzinfo.utcoffset() returned 1440; must be in -1439 .. 1439


Note that although only offsets within 24 hours are supported, it seems to be possible to use astimezone() with arbitrary offsets. So perhaps we gain consistency in removing the restriction altogether?

This would not be unprecedented. RFC 2822 allows any offset
representable as HHMM: "the zone MUST be within the range -9959
through +9959" Section 3.3 of http://tools.ietf.org/html/rfc2822.html