pytz: _utcoffset has a wrong value for Iran

python, pytz, timezone, utc

Solution

Let's see what's going on here:

>>> tz = pytz.timezone('Asia/Tehran')
>>> tz
<DstTzInfo 'Asia/Tehran' LMT+3:26:00 STD>

This means the timezone is expressed in LMT - which is solar time. That's why you see an utcoffset of 12360 - no error here, it's just calculated using a different reference.

Now if you do:

>>> d = tz.localize(datetime(2013, 1, 1))
>>> d
datetime.datetime(2013, 1, 1, 0, 0, tzinfo=<DstTzInfo 'Asia/Tehran' IRST+3:30:00 STD>)
>>> d.utcoffset()
datetime.timedelta(0, 12600)

The `localize` method caused the representation to switch to the correct time zone used at that date and place, which is IRST with an utcoffset of 12600 seconds.

And that's just what the `utcoffset` method of the tzinfo object does - it localizes the given datetime object and returns it's utcoffset.

Likewise if you currently do:

>>> d = datetime.now(tz)
>>> d
datetime.datetime(2013, 8, 15, 20, 46, 4, 705896, tzinfo=<DstTzInfo 'Asia/Tehran' IRDT+4:30:00 DST>)
>>> d.utcoffset()
datetime.timedelta(0, 16200)

You'll get the datetime expressed in IRDT because currently daylight saving time is in effect in that timezone.

Problem

Correct value: ``` >>> pytz.timezone('Asia/Tehran').utcoffset(datetime(2013, 1, 1)).total_seconds()/3600.0 3.5 >>> pytz.timezone('Asia/Tehran').utcoffset(datetime(2013, 1, 1)).total_seconds() 12600.0 ``` Incorrect value: ``` >>> pytz.timezone('Asia/Tehran')._utcoffset.total_seconds()/3600.0 3.433333333333333 >>> pytz.timezone('Asia/Tehran')._utcoffset.total_seconds() 12360.0 ``` I wonder if that `_utcoffset` attribute is used in `utcoffset()` method, why the method is working while the attribute is wrong. Looks like a bug anyway. Nothing changes if you replace `Asia/Tehran` with `Iran` ``` >>> print pytz.VERSION 2012c ``` OS: Linux Mint 15 (Olivia) Using Python 2.7

Original source