使用SWIG创建C库的Python绑定存在问题。

Question

我想使用SWIG为C库创建Python绑定，但我遇到了一些问题。我从教程中使用了以下.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，我遇到了这个问题：

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

非常感谢您的帮助

- Judicator

Answer 1

SWIG默认生成一个以下划线为前缀的模块，因此您将得到一个名为_example的模块，需要将其命名为_example.so。

这在SWIG文档34.2.3手动编译动态模块中有解释。

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.

- Antti Haapala -- Слава Україні