UTC time with offset:
>>> import pytz
>>> tz = pytz.timezone('Pacific/Apia')
>>> import datetime
>>> datetime.datetime(2011, 12, 30, 9, 59, tzinfo=datetime.timezone.utc).astimezone(tz).isoformat()
'2011-12-29T23:59:00-10:00'
>>> datetime.datetime(2011, 12, 30, 10, 00, tzinfo=datetime.timezone.utc).astimezone(tz).isoformat()
'2011-12-31T00:00:00+14:00'
Local time:
>>> '{:%Y-%m-%d %H:%M}'.format(datetime.datetime(2011, 12, 30, 9, 59, tzinfo=datetime.timezone.utc).astimezone(tz))
'2011-12-29 23:59'
>>> '{:%Y-%m-%d %H:%M}'.format(datetime.datetime(2011, 12, 30, 10, 00, tzinfo=datetime.timezone.utc).astimezone(tz))
'2011-12-31 00:00'