Problem when import C model

[baileyxia@gmail.com]

Hi, all
I am learning how to import c code in python.
Here is my simple code foo.c:
=============== ======
#include <Python.h>
void bar()
{
printf("Hello! C wrap!");
}
static PyObject *foo_bar(PyObje ct *self, PyObject *args) {
/* Do something interesting here. */
bar();
Py_RETURN_NONE;
}
static PyMethodDef foo_methods[] = {
{ "bar", (PyCFunction)fo o_bar, METH_NOARGS, NULL },
{ NULL, NULL, 0, NULL }
};
PyMODINIT_FUNC initfoo() {
Py_InitModule3( "foo", foo_methods, "My first extension module.");
}
=============== ======
I use gcc to compile the foo.c:
gcc -shared -I/usr/local/python/2.4.2/include/python2.4 -fPIC foo.c -o
foo.so

Problem is:
I can import foo on linux 64-bit platform if I also run gcc on linux
64-bit platform.
But I can not import foo on linux 64-bit platform if I run gcc on linux
32-bit platform.
Here is the error messege:
=============== ======
traceback (most recent call last):
File "<stdin>", line 1, in ?
ImportError: ./foo.so: cannot open shared object file: No such file or
directory
=============== ======

I can not figure out what cause this problem. wrong gcc option? wrong
python code?

[cmdrrickhunter@yaho.com]

Re: Problem when import C model

this is more of a linux question than a python question, so you may get
better luck with asking there.

What you describe makes perfect sense to me. If python is a 64 bit
program, it can only link to 64 bit libraries. If you compiled your
library in 32-bit mode, then the library headers will indicate this,
and linux's library loading code will ignore it when loading libraries
for 64-bit programs.

I think there' might be a trick that lets you compile ELF files with
both 64-bit and 32-bit code, but actually doing so is outside of my
expertise.
baileyxia@gmail .com wrote:

Hi, all
I am learning how to import c code in python.
Here is my simple code foo.c:
=============== ======
#include <Python.h>
void bar()
{
printf("Hello! C wrap!");
}
static PyObject *foo_bar(PyObje ct *self, PyObject *args) {
/* Do something interesting here. */
bar();
Py_RETURN_NONE;
}
static PyMethodDef foo_methods[] = {
{ "bar", (PyCFunction)fo o_bar, METH_NOARGS, NULL },
{ NULL, NULL, 0, NULL }
};
PyMODINIT_FUNC initfoo() {
Py_InitModule3( "foo", foo_methods, "My first extension module.");
}
=============== ======
I use gcc to compile the foo.c:
gcc -shared -I/usr/local/python/2.4.2/include/python2.4 -fPIC foo.c -o
foo.so
>
Problem is:
I can import foo on linux 64-bit platform if I also run gcc on linux
64-bit platform.
But I can not import foo on linux 64-bit platform if I run gcc on linux
32-bit platform.
Here is the error messege:
=============== ======
traceback (most recent call last):
File "<stdin>", line 1, in ?
ImportError: ./foo.so: cannot open shared object file: No such file or
directory
=============== ======
>
I can not figure out what cause this problem. wrong gcc option? wrong
python code?

[Nick Craig-Wood]

Re: Problem when import C model

cmdrrickhunter@ yaho.com <conrad.ammon@g mail.comwrote:

What you describe makes perfect sense to me. If python is a 64 bit
program, it can only link to 64 bit libraries. If you compiled your
library in 32-bit mode, then the library headers will indicate this,
and linux's library loading code will ignore it when loading libraries
for 64-bit programs.

32 bit and 64 bit are completely different architectures - you can't
mix and match them in one executable.

The python solution is to use distutils and build a setup.py then you
can compile for each platform easily.

I think there' might be a trick that lets you compile ELF files
with both 64-bit and 32-bit code, but actually doing so is outside
of my expertise.

I don't think so.

You can choose which you compile with. On 32 bit you'll compile 32
bit by default. If you want 64 bit choose -m64, eg

echo <<'#END' >z.c
#include <stdio.h>
int main(void)
{
printf("Hello\n ");
return 0;
}
#END
gcc -c -m32 -o z32.o z.c
gcc -c -m64 -o z64.o z.c
file z*.o

gives

z32.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped
z64.o: ELF 64-bit LSB relocatable, AMD x86-64, version 1 (SYSV), not stripped

--
Nick Craig-Wood <nick@craig-wood.com-- http://www.craig-wood.com/nick