(OT) python file-truncate on fc10 zero-fills file: who to ask?

[John Pilkington]

Hi:  I'm asking here because this is the most fc10-oriented list that I 
use and I thought someone might know the answer.  I'd be happy to ask 
elsewhere but don't know where might be the best place.

I'm trying to do shrink-to-fit with video files on fc10 after tcrequant 
was deprecated.  vamps looks as if it will do the job but I think I need 
to chop off a few kb from the end of the input file first to avoid a 
failure exit.  I can do this with dd but that's slow and file truncation 
would be better.  I can't see a command-line truncate but since I am 
hacking the mythburn.py script I thought I had found the answer here, in 
truncate([size]) :

http://www.python.org/doc/2.5.2/lib/bltin-file-objects.html

I've tried that.  The file size shrinks as required but the result is 
zero-filled.  Here's some stripped-down test code:

         vobsize = os.path.getsize(source)
         write("Initial vobsize is %s bytes" % vobsize)

         vobsize -= 2048
         f=open(source,'wb')
         f.truncate( vobsize )
         f.close()

         vobsize = os.path.getsize(source)
         write("vobsize after truncation is %s bytes" % vobsize)

Is this a known problem with python, or in its fc10 implementation? 
Where would be the best place to ask how to do this job?

TIA

John Pilkington