[Python-Dev] Extension to dl module to allow passing strings from native function

Senko Rasic senko.rasic at gmail.com
Fri Aug 12 01:40:03 CEST 2005

Hi all,

recently I've tried to use dl module functionality to interface with
external C function.
(It was a quick hack so I didn't want to write wrapper code). To my
dismay I learned that
call method doesn't allow passing data by reference (since strings are
immutable in
python) - but passing pointers around and modifying caller's data is
used all the time
in C, so that makes dl practically useless.

I've hacked the method to allow mutable data, by allocating temporary
buffers for
all string arguments passed to it, calling the c function, and then
constructing new
strings from the data in those buffers and returning them in a tuple
together with function
return code.

Combined with pack/unpack from struct module, this allows passing any structure
to and from the external C function, so, imho, it's a useful thing to
have. To my knowledge,
this functionality can't be achieved in pure python programs, and
there's no alternative
dynamic loader module that can do it.

More info with examples:

(the tarball contains setup.py and my dlmodule.c version, for experimenting
without patching the official module, and patch made against (fairly recent) cvs
version of dlmodule.c)

Thoughts, comments? Could this be put in standard module, does it make
sense, etc?


Senko Rasic <senko at senko dot net>

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