Thanks for wanting to work on this.

It is a little hard to parse from the OP's initial post, but he is asking that %V and %u be supported by datetime.strptime, which they currently are not.  strptime is the generalized constructor for turning a string into a datetime, so no, a new constructor is not the right approach.

The code that implements the strptime method of datetime is in the file _strptime.py in Lib.  Your patch should be against that code.  (Note that this is pretty un-obvious, I had to dig a bit to figure it out!)