Python inbuilt datetime package has build in method to convert a datetime object to isoformat. Here is a example:
>>>from datetime import datetime
>>>date = datetime.strptime('Thu, 16 Dec 2010 12:14:05', '%a, %d %b %Y %H:%M:%S')
>>>date.isoformat()
output is
'2010-12-16T12:14:05'
I wrote this answer primarily for people, who work in UTC and doesn't need to worry about time-zones. You can strip off last 6 characters to get that string.
Python 2 doesn't have very good internal library support for timezones, for more details and solution you can refer to this answer on stackoverflow, which mentions usage of 3rd party libraries similar to accepted answer.