C ++ Python模块导入错误：“undefined symbol：Py_InitModule3”（Py_InitModule（））

Question

我刚开始尝试在C中编写我的第一个Python扩展模块，并使用https://www.tutorialspoint.com/python/python_further_extensions.htm中提供的说明。

我在Linux Mint 18.1上，在其virtualenv版本中使用Python 3.6.1。

作为第一步，我编写了一个非常简约的Python模块版本。

这是我的C代码：

include <Python.h>

static PyObject* uniqueCombinations(PyObject* self)
{
    return Py_BuildValue("s", "uniqueCombinations() return value (is of type 'string')");
}

static char uniqueCombinations_docs[] =
    "usage: uniqueCombinations(lstSortableItems, comboSize)\n";

static PyMethodDef uniqueCombinations_funcs[] = {
    {"uniqueCombinations", (PyCFunction)uniqueCombinations, 
     METH_NOARGS, uniqueCombinations_docs},
    {NULL}
};

void inituniqueCombinations(void)
{
    Py_InitModule3("uniqueCombinations", uniqueCombinations_funcs,
                   "Extension module uniqueCombinations v. 0.01");
}

这里是我用来编译C代码到uniqueCombinations.cpython-36m-x86_64-linux-gnu.so的setup.py文件的代码：

from distutils.core import setup, Extension

setup(name='uniqueCombinations', version='0.01',  \
      ext_modules=[Extension('uniqueCombinations', ['uniqueCombinations_pythonCmodule_v-0.01_Cg.c'])])

令我惊讶的是，导入时模块无法正确加载：

>>> import uniqueCombinations
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: uniqueCombinations.cpython-36m-x86_64-linux-gnu.so: undefined symbol: Py_InitModule3

为什么我收到此错误？

我该怎么做才能正确加载已编译的模块？

这里的构建协议带有关于Py_InitModule3的隐式声明的警告：

$ python uniqueCombinations_pythonCmodule_v-0.01_setup.py_Cg.py build
running build
running build_ext
building 'uniqueCombinations' extension
gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -I/usr/local/include/python3.6m -c uniqueCombinations_pythonCmodule_v-0.01_Cg.c -o build/temp.linux-x86_64-3.6/uniqueCombinations_pythonCmodule_v-0.01_Cg.o
uniqueCombinations_pythonCmodule_v-0.01_Cg.c: In function ‘inituniqueCombinations’:
uniqueCombinations_pythonCmodule_v-0.01_Cg.c:19:5: warning: implicit declaration of function ‘Py_InitModule3’ [-Wimplicit-function-declaration]
     Py_InitModule3("uniqueCombinations", uniqueCombinations_funcs,
     ^
creating build/lib.linux-x86_64-3.6
gcc -pthread -shared build/temp.linux-x86_64-3.6/uniqueCombinations_pythonCmodule_v-0.01_Cg.o -o build/lib.linux-x86_64-3.6/uniqueCombinations.cpython-36m-x86_64-linux-gnu.so

Answer 1

不再使用Py_InitModule（Py_InitModule3）。 有必要改为创建PyModuleDef结构，然后将对它的引用传递给PyModule_Create。

在导入时创建的模块不会引发错误的C代码下面：

#include <Python.h>

static PyObject* uniqueCombinations(PyObject* self)
{
    return Py_BuildValue("s", "uniqueCombinations() return value (is of type 'string')");
}

static char uniqueCombinations_docs[] =
    "usage: uniqueCombinations(lstSortableItems, comboSize)\n";

/* deprecated: 
static PyMethodDef uniqueCombinations_funcs[] = {
    {"uniqueCombinations", (PyCFunction)uniqueCombinations, 
     METH_NOARGS, uniqueCombinations_docs},
    {NULL}
};
use instead of the above: */

static PyMethodDef module_methods[] = {
    {"uniqueCombinations", (PyCFunction) uniqueCombinations, 
     METH_NOARGS, uniqueCombinations_docs},
    {NULL}
};


/* deprecated : 
PyMODINIT_FUNC init_uniqueCombinations(void)
{
    Py_InitModule3("uniqueCombinations", uniqueCombinations_funcs,
                   "Extension module uniqueCombinations v. 0.01");
}
*/

static struct PyModuleDef Combinations =
{
    PyModuleDef_HEAD_INIT,
    "Combinations", /* name of module */
    "usage: Combinations.uniqueCombinations(lstSortableItems, comboSize)\n", /* module documentation, may be NULL */
    -1,   /* size of per-interpreter state of the module, or -1 if the module keeps state in global variables. */
    module_methods
};

PyMODINIT_FUNC PyInit_Combinations(void)
{
    return PyModule_Create(&Combinations);
}

这里的构建协议：

$ python uniqueCombinations_pythonCmodule_v-0.01_setup.py_Cg.py build
running build
running build_ext
building 'Combinations' extension
gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -I/usr/local/include/python3.6m -c uniqueCombinations_pythonCmodule_v-0.01_Cg.c -o build/temp.linux-x86_64-3.6/uniqueCombinations_pythonCmodule_v-0.01_Cg.o
gcc -pthread -shared build/temp.linux-x86_64-3.6/uniqueCombinations_pythonCmodule_v-0.01_Cg.o -o build/lib.linux-x86_64-3.6/Combinations.cpython-36m-x86_64-linux-gnu.so

和成功导入的交互式Python控制台会话：

>>> import Combinations
>>> dir(Combinations)
['__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'uniqueCombinations']
>>> Combinations.__doc__
'usage: Combinations.uniqueCombinations(lstSortableItems, comboSize)\n'
>>> Combinations.uniqueCombinations()
"uniqueCombinations() return value (is of type 'string')"
>>>