As this question comes often, here is the simple explanation.
datetime or time module has two important functions.
In both cases, we need a formating string. It is the representation that tells how the date or time is formatted in your string.
Now lets assume we have a date object.
>>> from datetime import datetime
>>> d = datetime(2010, 2, 15)
>>> d
datetime.datetime(2010, 2, 15, 0, 0)
If we want to create a string from this date in the format 'Mon Feb 15 2010'
>>> s = d.strftime('%a %b %d %y')
>>> print s
Mon Feb 15 10
Lets assume we want to convert this s again to a datetime object.
>>> new_date = datetime.strptime(s, '%a %b %d %y')
>>> print new_date
2010-02-15 00:00:00
Refer This document all formatting directives regarding datetime.