[Pyrex] Pyrex versus ctypes

[Bob Ippolito]

On Jun 10, 2004, at 6:01 PM, David McNab wrote:

> After a year or so's hacking with Pyrex, I've come across the 'ctypes' 
> package (http://starship.python.net/crew/theller/ctypes/).
>
> ctypes allows the calling of C functions from *pure-python* code, 
> without requiring the generation/compilation of a C wrapper module.
>
> Pure python code using ctypes can even receive callbacks from C funcs, 
> and manipulate C data structures, pretty much most of what one would 
> need for interfacing with C.
>
> All this feels too good to be true.
>
> Can anyone offer some thoughts on the ideal demarcation lines between 
> Pyrex and ctypes, and some thoughts on pros and cons, and which 
> situations indicate Pyrex over ctypes and vice versa?
>
> For instance, how severe are ctypes' overheads with constructing the C 
> call frame, and rendering the return back to python?

Here's a few ctypes disadvantages off the top of my head (I hope the 
advantages are obvious, since we're all Python users here, so I won't 
list them):

ctypes can be one royal pain in the ass to debug.  There are still bugs 
in *it*, at least on non-win32 platforms.  I would wait a release or 
two unless you have very simple requirements (bugs that I've seen are 
pretty much limited to structure packing and python callbacks) or want 
to become a committer too :)

ctypes is not designed for speed, I'm not sure exactly what the 
overhead is, but I guarantee it's more than Pyrex.

It takes more time to wrap a C API with ctypes than with Pyrex because 
you can't leverage anything that the C compiler and preprocessor knows 
about.

It's not possible to poke back inside the Python C API with ctypes at 
this time (since it releases the GIL and has no GIL-holding call 
facility, though it wouldn't be too hard to make one).

-bob
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