python - 如何从 Python 扩展模块的 C 代码调用内置函数(或方法)？

Question

我目前想要完成的是调整 Pythons itertools 模块函数 combinations 以在创建组合之前对传递的 iterable 进行排序对返回的组合进行排序的目标。

我是第一次使用 Python 扩展模块，到目前为止我唯一的经验是编写和编译类似 Python 扩展模块的“Hello World”，但我希望我的整体编程经验能在几个编程中得到提升语言是我可以在这一挑战上取得成功的坚实基础。

我知道有一个内置的 Python 函数 sorted() 可以对传递给 combinations 的 iterable 进行排序，但我不知道如何在扩展模块的C代码。

我试过只写 iterable = sorted(iterable); 但即使模块编译(带有警告)编译模块的导入失败并显示 ImportError: cgitertools.cpython -36m-x86_64-linux-gnu.so: undefined symbol :已排序

我的问题是:

How to call the Pythons builtin method (using as example sorted()) from within C code of a Python extension module?

下面是我尝试过的所有细节以及为什么它不起作用:

combinations_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    combinationsobject *co;
    Py_ssize_t n;
    Py_ssize_t r;
    PyObject *pool = NULL;
    PyObject *iterable = NULL;
    Py_ssize_t *indices = NULL;
    Py_ssize_t i;
    static char *kwargs[] = {"iterable", "r", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "On:combinations", kwargs,
                                     &iterable, &r))
        return NULL;

    // iterable.sort(); doesn't work ... cgitertoolsmodule.c:2398:13: error: request for member ‘sort’ in something not a structure or union
    // iterable.__sort__(); doesn't work either with same error
    // COMPILES, but gives ERROR on import in Python: 
    iterable = sorted(iterable);

$ python3.6 cgitertoolsmodule-setup.py build
running build
running build_ext
building 'cgitertools' extension
gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -I/usr/local/include/python3.6m -c cgitertoolsmodule.c -o build/temp.linux-x86_64-3.6/cgitertoolsmodule.o
cgitertoolsmodule.c: In function ‘combinations_new’:
cgitertoolsmodule.c:2400:16: warning: implicit declaration of function ‘sorted’ [-Wimplicit-function-declaration]
     iterable = sorted(iterable);
                ^
cgitertoolsmodule.c:2400:14: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
     iterable = sorted(iterable);
              ^
gcc -pthread -shared build/temp.linux-x86_64-3.6/cgitertoolsmodule.o -o build/lib.linux-x86_64-3.6/cgitertools.cpython-36m-x86_64-linux-gnu.so

$ python3.6
Python 3.6.1 (default, Apr 18 2017, 23:00:41) 
[GCC 5.4.1 20160904] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from cgitertools import combinations
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cgitertools.cpython-36m-x86_64-linux-gnu.so: undefined symbol: sorted

Answer 1

您应该从内置函数中获取 sorted 函数，然后调用它:

PyObject *builtins = PyEval_GetBuiltins(); 
PyObject *sorted = PyDict_GetItemString(builtins , "sorted");
PyObject *sorted_list = PyEval_CallFunction(sorted, "(O)", iterable);

//... do something with the sorted_list

Py_DECREF(sorted_list);