Wrapping C with Python

[Anish Chapagain]

Hi!!
I tried wrapping a simple C code suing SWIG to Python, but am having
problem,
my .c file is,

Step 1:
example.c
--------------
double val=3.0;
int fact(int n)
{
if(n<=1)
return 1;
else
return n*fact(n-1);
}

int mod(int x, int y)
{
return (x%y);
}

Step 2:
I then created interface file as.
example.i
--------------
%module example
%{
%}
extern int fact(int n);
extern int mod(int x,int y);

Step 3:
I compiled the .i file with SWIG,
c:\python25\swi gswig -
python example.i
It creates example.py and example_wrap.c

Step 4:
I compiled example.c and example_wrap.c individually
c:\python25\min gw\bin gcc -c example.c (it create
example.o)
c:\python25\min gw\bin gcc -c example_wrap.c -Ic:
\python25\inclu de (it create example_wrap.o)

Step 5:
building .pyd for windows,
c:\python25\min gw\bin gcc -shared *.o -o _example.pyd -Lc:
\python25\libs -lpython25 (it creates _example.pyd)


Then, i imported example module by palcing it in python25 directory,
it get's imported but i'm not able to use function, when i called

>>>print example.fact(4)
>>>print example.mod(4,2 )

It is nither showing any error nor message...
even i tried simple void fact() by printf inside .c file and is not
showing ...

hope for help...
regard's
Anish

[RPM1]

Re: Wrapping C with Python

Anish Chapagain wrote:

Hi!!
I tried wrapping a simple C code suing SWIG to Python, but am having
problem,

I am not too familiar with SWIG, (I have looked at it), but you may want
to try ctypes in the standard module library. It's very easy to use. I
use it on Windows with gcc but I believe it works fine on Linux too.
Basically you just compile your C code as a regular C code dll. ctypes
then allows you to access the functions in the dll very easily. I was
concerned that performance might be an issue but that has turned out not
to be true. I'm writing a chess program and the C dll handles the move
generation so it is getting called a lot. So far it runs at about
200,000 calls per second.

Patrick

[brad]

Re: Wrapping C with Python

RPM1 wrote:
....

Basically you just compile your C code as a regular C code dll. ctypes
then allows you to access the functions in the dll very easily.

Does that work with C++ code too or just C?

[Anish Chapagain]

Re: Wrapping C with Python

On 4 Aug, 14:14, brad <byte8b...@gmai l.comwrote:

RPM1 wrote:
>
...
>

Basically you just compile your C code as a regular C code dll.  ctypes
then allows you to access the functions in the dll very easily.

>
Does that work with C++ code too or just C?

Hi..
I havenot tried..before with dll, is there any help material and for
me my API in C has almost 20 c files, so will it be feasible

anish

[Stefan Behnel]

Re: Wrapping C with Python

Anish Chapagain wrote:

I tried wrapping a simple C code suing SWIG to Python, but am having
problem,

Try Cython. It's a Python-like language between Python and C that compiles to
C code. It makes it very easy to call into C functions and to hide them behind
a nice Python module.

http://cython.org/

Stefan

[RPM1]

Re: Wrapping C with Python

brad wrote:

RPM1 wrote:
...

>Basically you just compile your C code as a regular C code dll.
>ctypes then allows you to access the functions in the dll very easily.

>
Does that work with C++ code too or just C?

I believe it does work with C++ although I have not done that. Here's a
simple example:

http://wolfprojects.altervista.org/dllforpyinc.php

I bet if you google around you'll find what you need.

Remember there is documentation for ctypes in the Python documentation
that comes with Python.

Patrick

[RPM1]

Re: Wrapping C with Python

Anish Chapagain wrote:

On 4 Aug, 14:14, brad <byte8b...@gmai l.comwrote:

>RPM1 wrote:
>>
>...
>>

>>Basically you just compile your C code as a regular C code dll. ctypes
>>then allows you to access the functions in the dll very easily.

>Does that work with C++ code too or just C?

>
Hi..
I havenot tried..before with dll, is there any help material and for
me my API in C has almost 20 c files, so will it be feasible
>
anish

It is worth looking into it. I found ctypes to be very easy. I had the
example up and running in minutes. I have also figured out how to do
things like return arrays to Python. It isn't that hard. I like the
fact that I don't have to think about reference counting or PyObjects
etc. If you are doing simple function calls ctypes is very easy.

My C code looks like C code. It has no Python stuff at all. My Python
code has just a few calls to the ctypes module. I guess that's one
thing I like about it is that my C code looks like C code and my Python
code looks like Python code, (not much spilling over).

I'm sure it's not perfect, but it seems a lot easier than SWIG to me.

Patrick

[Terry Reedy]

Re: Wrapping C with Python



brad wrote:

RPM1 wrote:
...

>Basically you just compile your C code as a regular C code dll.
>ctypes then allows you to access the functions in the dll very easily.

>
Does that work with C++ code too or just C?

On Windows, You can apparently works either with stdcall or cdecl functions.
"ctypes tries to protect you from calling functions with the wrong
number of arguments or the wrong calling convention. Unfortunately this
only works on Windows. It does this by examining the stack after the
function returns, so although an error is raised the function has been
called:" "To find out the correct calling convention you have to look
into the C header file or the documentation for the function you want to
call." I do not know if these are only C-isms or also C++-isms.

[Uwe Schmitt]

Re: Wrapping C with Python

On 4 Aug., 15:14, brad <byte8b...@gmai l.comwrote:

RPM1 wrote:
>
...
>

Basically you just compile your C code as a regular C code dll.  ctypes
then allows you to access the functions in the dll very easily.

>
Does that work with C++ code too or just C?

It works if the interface of the DLL is C-style, that is you declare
your
functions with 'extern "C" { .... }' around them.
Inside your modules implementation you can use C++ without any
problems.

What works fine too, is f2py from numpy. It targets at wrapping
Fortran
code, but is able to wrap C code too, see

http://www.scipy.org/Cookbook/f2py_and_NumPy?action=show

Greetings, Uwe

Greetings, Uwe