---------- Forwarded message ---------- From: Stefan Behnel <[EMAIL PROTECTED]> Date: Oct 11, 2007 11:19 AM Subject: Re: [Pyrex] C-API implementation in Pyrex 0.9.6 To: William Stein <[EMAIL PROTECTED]> Cc: sage-devel@googlegroups.com, Greg Ewing <[EMAIL PROTECTED]>, Pyrex ML <[EMAIL PROTECTED]>
William Stein wrote: > Can I ask a few naive questions about "the C-API support", since I know that > me and _many_ of the people I work with are confused about what this support > provides? I'll just ask a few naive questions, and maybe your answers would > be useful for me to add to the faq or documentation. Sure. The main idea behind the C-API support for Pyrex/Cython is to automate this: http://docs.python.org/ext/using-cobjects.html > (1) Suppose I would like to define a cdef'd function in a module > arith.pyx that I want > to call from other .pyx files, e.g., > > cdef int fast_gcd(int a, int b): > ... > > Then I basically want to do this sort of thing from other .pyx files: > from arith cimport fast_gcd > int x = fast_gcd(5,7) > > Definitely in Cython/Pyrex a few months ago the above wouldn't work. > Is there a way to make it work now? Yes. You can export the function from arith.pyx via the "api" keyword (in Pyrex 0.9.6, Cython will follow here) and it will generate a file "arith_api.h" and (if you want) a .pxd file that define it. Then the above code should work. > And if so, what are the linking > requirements (i.e. options to gcc or distutils)? No linking required, pure runtime access. > (2) Suppose I want to define a cdef'd function in a .pyx file, as above, but > now > I want it to be callable from some external C file. E.g., > > /* this is a C function in a .c file */ > int foo(blah) { > fast_gcd(...) > } > > This is very natural to do because I might be mixing C and .pyx code, > and this provides a way to reach back and get at Python data directly > from C code. Is there now a way to do this? In exactly the same way, just with a little less automatism. The arith_api.h files defines static function pointers for each exported function and a static function that you can call to initialise the pointers based on the Python module. So, #including the header file and calling that function is enough to do the above. To make my position regarding the Pyrex 0.9.6 implementation clear: I like the Pyrex interface to this functionality, it is better and cleaner than my original implementation, and Cython should follow here. I just dislike the internal implementation that leaks too much into Python space, where it simply does not belong at all. Stefan -- William Stein Associate Professor of Mathematics University of Washington http://wstein.org --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
