为 C 库创建 Python 绑定的 SWIG 问题

Question

我想使用 SWIG 为 C 库创建 Python 绑定，但我遇到了一些麻烦。我使用了教程中的以下 .c 和 .i 文件。 example.c

/* Compute factorial of n */
int fact(int n) {
  if (n <= 1)
    return 1;
  else
    return n*fact(n-1);
}

/* Compute n mod m */
int my_mod(int n, int m) {
  return(n % m);
}

double My_variable;

example.i

%module example
%{
extern double My_variable;
extern int    fact(int);
extern int    my_mod(int n, int m);
%}

extern double My_variable;
extern int    fact(int);
extern int    my_mod(int n, int m);

我使用的命令：

$ swig -python -py3 example.i
$ gcc -c -fpic example.c example_wrap.c -I/usr/include/python3.6
$ gcc -shared example.o example_wrap.o -o example.so

当我尝试在 python3 中导入它时，我得到了这个

>>> import example
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dynamic module does not define module export function (PyInit_example)

感谢任何帮助

Answer 1

SWIG 生成一个默认带有 下划线前缀的模块 ，因此您将得到一个名为 _example 的模块，它需要位于 _example.so 中。

这在SWIG documentation 34.2.3 Hand compiling a dynamic module中有解释：

While the preferred approach to building an extension module is to use the distutils, some people like to integrate building extensions with a larger build system, and thus may wish to compile their modules without the distutils. To do this, you need to compile your program using commands like this (shown for Linux):
$ swig -python example.i
$ gcc -O2 -fPIC -c example.c
$ gcc -O2 -fPIC -c example_wrap.c -I/usr/local/include/python2.5
$ gcc -shared example.o example_wrap.o -o _example.so
The exact commands for doing this vary from platform to platform. However, SWIG tries to guess the right options when it is installed. Therefore, you may want to start with one of the examples in the SWIG/Examples/python directory. If that doesn't work, you will need to read the man-pages for your compiler and linker to get the right set of options. You might also check the SWIG Wiki for additional information.

When linking the module, the name of the output file has to match the name of the module prefixed by an underscore. If the name of your module is example, then the name of the corresponding object file should be _example.so or _examplemodule.so. The name of the module is specified using the %module directive or the -module command line option.

Compatibility Note: In SWIG-1.3.13 and earlier releases, module names did not include the leading underscore. This is because modules were normally created as C-only extensions without the extra Python support file (instead, creating Python code was supported as an optional feature). This has been changed in SWIG-1.3.14 and is consistent with other Python extension modules. For example, the socket module actually consists of two files; socket.py and _socket.so. Many other built-in Python modules follow a similar convention.

为 C 库创建 Python 绑定的 SWIG 问题

Issue with SWIG for creating Python bindings for C library

python

c

swig

python-c-api