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

[John Pilkington]

Patrick O'Callaghan wrote:
> On Thu, 2009-03-05 at 15:32 +0000, John Pilkington wrote:
>> 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?
> 
> I've no idea, but I suspect you could probably write a tiny C program to
> do the truncation is less time than it would take to get an answer.
> 
> poc
> 

For the record - ie in case someone comes to this by Google - the 
problem was solved by using f=open(source,'ab'), which opens the binary 
file in append mode.

John P