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Reopening to deal with the error Tony caught.

Tony, can you apply the included patch and verify it works for you okay?  
I added another if to track back a week if the calculation gets pushed 
past 366 days.  That does fix your error.  And if you can think of any 
other edge cases let me know.  I think that should cover everything.

And yes, the example for the OP is wrong::

>>> datetime.date(2004, 10, 11).strftime("%Y %U %w")
'2004 41 1'