>>> gmt = pytz.timezone('GMT')
>>> eastern = pytz.timezone('US/Eastern')
>>> d = datetime.datetime(2014,03,21,7)
>>> dateeastern = eastern.localize(d)
>>> dateeastern
datetime.datetime(2014, 3, 21, 7, 0, tzinfo=<DstTzInfo 'US/Eastern' EDT-1 day, 20:00:00 DST>)
>>> dategmt = dateeastern.astimezone(gmt)
>>> dategmt
datetime.datetime(2014, 3, 21, 11, 0, tzinfo=<StaticTzInfo 'GMT'>)
Replace GMT with UTC:
>>> eastern = pytz.timezone('US/Eastern')
>>> d = datetime.datetime(2014,03,21,7)
>>> dateeastern = eastern.localize(d)
>>> dateeastern
datetime.datetime(2014, 3, 21, 7, 0, tzinfo=<DstTzInfo 'US/Eastern' EDT-1 day, 20:00:00 DST>)
>>> dateutc = dateeastern.astimezone(pytz.utc)
>>> dateutc
datetime.datetime(2014, 3, 21, 11, 0, tzinfo=<UTC>)