datetime.timedelta is now subclassable in Python. The new test shows

datetime.timedelta is now subclassable in Python.  The new test shows
one good use:  a subclass adding a method to express the duration as
a number of hours (or minutes, or whatever else you want to add).  The
native breakdown into days+seconds+us is often clumsy.  Incidentally
moved a large chunk of object-initialization code closer to the top of
the file, to avoid worse forward-reference trickery.