How to get the common name for a pytz timezone eg. EST/EDT for America/New_York

Given a pytz timezone for a particular user(calculated from his offset), i want to display the common name for that timezone. I'm assuming people are more accustomed to seeing EST or PST instead of spelled out like America/NewYork.

If you need this derived from a datetime object localized with pytz...

>>> import pytz as tz
>>> from datetime import datetime as dt
>>> CT = tz.timezone('America/Chicago')
>>>
>>> summer_day = dt(2010, 7, 4, 0, 1, 1)
>>> bar = CT.localize(summer_day, is_dst=None)
>>> bar.tzname()
'CDT'
>>>
>>> christmas = dt(2010, 12, 25, 0, 1, 1)
>>> foo = CT.localize(christmas, is_dst=None)
>>> foo.tzname()
'CST'
>>> 

You can use the tzname() method of tzinfo instances:

>>> tz = timezone('America/St_Johns')
>>> normal = datetime(2009, 9, 1)
>>> tz.tzname(normal, is_dst=False)
'NDT'