How to bypass Windows 'cooking' the I/O? (One more time, please)

Larry Bates larry.bates at`
Fri Jul 4 02:56:46 CEST 2008

norseman wrote:
> I know I saw the answer recently, as in since February '08, but I can't 
> re-find it. :(   I tried the mail archives and such and my own 
> collections but the piece I saw still eludes me.
> Problem:  (sos=same old s...)  Microsoft insists the world work it's way 
> even when the Microsoft way was proven wrong decades ago. In this case 
> it's (still) 'cooking' the writes even with 'rwb' and O_RDWR|O_BINARY in 
> (proper respective) use.
> Specific:  python created and inspected binary file ends:
>        00460: 0D 1A        (this is correct)
>        after a write
>             os.lseek(target, -1, 2)
>             os.write(target,record)
>        the expected result would be:
>        00460: 0D 20 bytes.... 1A
>        BUT I get:
>        00460: 20 .... data bytes... 1A
> It is one byte off!!!  And the 0D has to be there. Signifies the end of 
> the header.
> Same python program runs as expected in Linux.  Maybe because that's 
> where it was written?! :)
> What I seek is the way to slap Microsoft up side the head and make it 
> work correctly.  OK, well, at least in this situation.
> Note: Things like this justify Python implementers bypassing OS calls 
> (data fetch, data write) and using the BIOS direct. Remember, the CPU 
> understands bit patterns only. It has no comprehension of 'text', 
> 'program', 'number', 'pointer', blah blah blah....  All that is totally 
> beyond it's understanding. A given bit pattern means 'do that'. The CPU 
> is 100% binary.  Memory, storage and the rest is just bits-on, bits-off.
> Patterns. Proper binary I/O is mandatory for the machine to function.
> Anyway - if whoever mentioned the flags and such to 'over ride' 
> Microsoft's BS would re-send that piece I would be very appreciative.
> Steve
> norseman at

Since you didn't show any code context, I'll try my mind reading superpowers.....

You may be the victim of buffering (not calling .flush() or .close() to commit 
your write to disk).  Why aren't you using the file object to do you seek and write?

Normal file I/O sequence:

fp = open(target, 'wb'), 2)


by going through os. methods instead of the file instance I think you are 
accessing the file through 2 different I/O buffers.  I could be all wrong here.


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