[Python-Dev] Identifying magic prefix on Python files?

[Fredrik Lundh]

eric wrote:

> Python's .pyc files don't have a magic prefix that the file(1) utility
> can recognize.  Would anyone object if I fixed this?  A trivial pair of
> hacks to the compiler and interpreter would do it.  Backward compatibility
> would be easily arranged.
> 
> Embedding the Python version number in the prefix might enable some
> useful behavior down the road.

Python 1.5.2 (#0, May  9 2000, 14:04:03)
>>> import imp
>>> imp.get_magic()
'\231N\015\012'

Python 2.0 (#8, Jan 29 2001, 22:28:01)
>>> import imp
>>> imp.get_magic()
'\207\306\015\012'
>>> open("some_module.pyc", "rb").read(4)
'\207\306\015\012'

Python 2.1a1 (#9, Jan 19 2001, 08:41:32)
>>> import imp
>>> imp.get_magic()
'\xdc\xea\r\n'

if you want to change the magic, there are a couple
things to consider:

1) the header must consist of imp.get_magic() plus
a 4-byte timestamp, followed by a marshalled code
object

2) the magic should be four bytes.

3) the magic must be different for different bytecode
versions

4) the magic shouldn't survive text/binary conversions
on platforms which treat text files and binary files diff-
erently.

Cheers /F