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 以在创建目标组合之前对传递的 iterable 进行排序对返回的组合进行排序。

我是第一次开发 Python 扩展模块，到目前为止我唯一的经验是编写和编译 "Hello World" 类似 Python 扩展模块，但我希望我在几种编程语言方面的总体编程经验是一个足够坚实的基础，我可以在此基础上成功应对这一挑战。

我知道有一个内置的 Python 函数 sorted() 可以对传递给 combinations 的可迭代对象进行排序，但我不知道如何从 C 代码中调用它的扩展模块。

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 ImportError: cgitertools.cpython-36m-x86_64-linux-gnu.so: undefined symbol: sorted

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);

如何从 Python 扩展模块的 C 代码调用内置函数（或方法）？

How to call a builtin function (or method) from C code of a Python extension module?

python

c

python-3.x

itertools

extension-modules