[Robert McLay]
> I'm trying to understand bytecodes generated on different machines.
> I understand that the bytecodes can change between version. But since
> I'm told that .pyc files are version dependent but not machine
> dependent, I'm wondering why the bytecodes are machine dependent.
They aren't -- at least not particularly <wink>.
> my friend and I created this simple example to explore the problem.
> The example code is:
>
> #!/usr/bin/env python
> #
> import sys, os
>
> def main():
> x = 1.234
> print x
>
> if ( __name__ == '__main__'):
> main()
>
>
> Using sib.py from Vendorid 1.0 generates different bytecodes under linux
> and sgi. At its core sib.py is using:
>
> # Compile the code using prefix and marshall it.
> compiled_code = compile(source_code, prefix, 'exec')
> marshalled_code = marshal.dumps(compiled_code)
>
> to get the bytecodes.
Why do you believe that `prefix` had the same value in both runs? The
output suggests it did not, but can't guess more than that from here
since I don't know where `prefix` came from.
> So why are the byte codes different? Is it that the intel-linux is
> little endian and the SGI is big endian
No; marshal format has fixed endianness.
> and the numerical constant (1.234) is stored different depending on the
> endian-ness?
Python defers to the platform C library for string->float conversions,
and it's *possible* that different platforms could convert "1.234" to
a C double in slightly different ways. There's no evidence of that
here, though.
> This was generated under intel-linux using python 2.4.2
>
>
>
>
>
> /*==========================================================================*/
> /* Frozen main script for test
> */
> /* Generated from test.py
> */
> /* This is generated code; Do not modify it!
> */
>
> /*--------------------------------------------------------------------------*/
> unsigned char M___main__[] =
> {
> 99,0,0,0,0,0,0,0,0,2,0,0,0,64,0,0,
> 0,115,55,0,0,0,100,0,0,107,0,0,90,0,0,100,
> 0,0,107,1,0,90,1,0,100,1,0,132,0,0,90,2,
> 0,101,3,0,100,2,0,106,2,0,111,11,0,1,101,2,
> 0,131,0,0,1,110,1,0,1,100,0,0,83,40,3,0,
> 0,0,78,99,0,0,0,0,1,0,0,0,1,0,0,0,
> 67,0,0,0,115,15,0,0,0,100,1,0,125,0,0,124,
> 0,0,71,72,100,0,0,83,40,2,0,0,0,78,102,5,
> 49,46,50,51,52,40,1,0,0,0,116,1,0,0,0,120,
> 40,1,0,0,0,82,0,0,0,0,40,0,0,0,0,40,
> 0,0,0,0,116,23,0,0,0,47,104,111,109,101,47,118, /* This
> line */
> 112,97,114,114,47,115,105,98,47,116,101,115,116,46,112,121,
> 116,4,0,0,0,109,97,105,110,5,0,0,0,115,4,0,
> 0,0,0,1,6,1,116,8,0,0,0,95,95,109,97,105,
> 110,95,95,40,4,0,0,0,116,3,0,0,0,115,121,115,
> 116,2,0,0,0,111,115,82,2,0,0,0,116,8,0,0,
> 0,95,95,110,97,109,101,95,95,40,3,0,0,0,82,4,
> 0,0,0,82,2,0,0,0,82,5,0,0,0,40,0,0,
> 0,0,40,0,0,0,0,82,1,0,0,0,116,1,0,0,
> 0,63,3,0,0,0,115,6,0,0,0,18,2,9,4,13,
> 1,
> }; x
>
> And under SGI (python 2.4.2) it created :
>
>
> /*==========================================================================*/
> /* Frozen main script for test
> */
> /* Generated from test.py
> */
> /* This is generated code; Do not modify it!
> */
>
> /*--------------------------------------------------------------------------*/
> unsigned char M___main__[] =
> {
> 99,0,0,0,0,0,0,0,0,2,0,0,0,64,0,0,
> 0,115,55,0,0,0,100,0,0,107,0,0,90,0,0,100,
> 0,0,107,1,0,90,1,0,100,1,0,132,0,0,90,2,
> 0,101,3,0,100,2,0,106,2,0,111,11,0,1,101,2,
> 0,131,0,0,1,110,1,0,1,100,0,0,83,40,3,0,
> 0,0,78,99,0,0,0,0,1,0,0,0,1,0,0,0,
> 67,0,0,0,115,15,0,0,0,100,1,0,125,0,0,124,
> 0,0,71,72,100,0,0,83,40,2,0,0,0,78,102,5,
> 49,46,50,51,52,40,1,0,0,0,116,1,0,0,0,120,
> 40,1,0,0,0,82,0,0,0,0,40,0,0,0,0,40,
> 0,0,0,0,116,23,0,0,0,47,87,111,114,107,47,118, /* This
> line */
> 112,97,114,114,47,115,105,98,47,116,101,115,116,46,112,121,
> 116,4,0,0,0,109,97,105,110,5,0,0,0,115,4,0,
> 0,0,0,1,6,1,116,8,0,0,0,95,95,109,97,105,
> 110,95,95,40,4,0,0,0,116,3,0,0,0,115,121,115,
> 116,2,0,0,0,111,115,82,2,0,0,0,116,8,0,0,
> 0,95,95,110,97,109,101,95,95,40,3,0,0,0,82,4,
> 0,0,0,82,2,0,0,0,82,5,0,0,0,40,0,0,
> 0,0,40,0,0,0,0,82,1,0,0,0,116,1,0,0,
> 0,63,3,0,0,0,115,6,0,0,0,18,2,9,4,13,
> 1,
> };
>
>
> The difference between the two is very slight:
>
> 18c18
> < 0,0,0,0,116,23,0,0,0,47,104,111,109,101,47,118,
> ---
> > 0,0,0,0,116,23,0,0,0,47,87,111,114,107,47,118,
Stare at this:
>>> ''.join(map(chr, [47,104,111,109,101,47,118]))
'/home/v'
>>> ''.join(map(chr, [47,87,111,114,107,47,118]))
'/Work/v'
It _suggests_ that `prefix` contained the substring "/home/" on one
box but ""/Work/" on the other.
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