PyObject_CallMethod返回空，提供简单示例。

Question

我是一名初学者Python程序员，正在将一些Python代码嵌入到C++ DLL中。无法使PyObject_CallMethod工作，每次调用Python 3.6类方法时都会返回Null。创建了一个小示例来说明这个问题，请查看代码中的注释。希望能得到一些关于我做错了什么的指导。

    #include "stdafx.h"

using namespace std;

int TestBasicStats()
{
    _putenv_s("PYTHONPATH", ".");

    Py_Initialize();

    PyObject* module = PyImport_ImportModule("BasicStats");
    assert(module != NULL); // Returned non-null object

    PyObject* MyPyClass = PyObject_GetAttrString(module, "BasicStats");
    assert(MyPyClass != NULL);// Returned non-null object

    PyObject* myClassInstance = PyInstanceMethod_New(MyPyClass);
    assert(myClassInstance != NULL);// Returned non-null object

    PyObject* result = PyObject_CallMethod(myClassInstance, "AddItem", "(i)", 1);
    assert(result != NULL); // Failed - returned NULL

    result = PyObject_CallMethod(myClassInstance, "AddItem", "(i)", 2);
    assert(result != NULL); // Failed - returned NULL

    result = PyObject_CallMethod(myClassInstance, "get_Max", NULL);
    assert(result != NULL); // Failed - returned NULL

    printf("Min = %ld\n", PyLong_AsLong(result));
    printf("Min = %f\n", PyFloat_AsDouble(result));

    Py_Finalize();

    return 0;
}


int main()
{
    TestBasicStats();

    return 0;
}

Python类的名称如下所示：

class BasicStats:
def __init__(self):
    self._m_min = self._m_max = self._m_sum = self._m_sumSqr = 0
    self._m_count = 0
    self.Reset()

def Reset(self):
    self._m_min = float("inf")
    self._m_max = float("-inf")
    self._m_sum = self._m_sumSqr = 0
    self._m_count = 0

def AddItem(self, value):
    self._m_count += 1
    if self._m_max < value:
        self._m_max = value

def get_Max(self):
    return self._m_max

Max = property(fget=get_Max)

- Vince

Answer 1

我不是很理解这里的PyInstanceMethod_New()调用。在我的代码中从未使用过，因此对其完全不确定它的功能。PyObject_GetAttrString()调用返回的PyObject应该是类型对象，并且可以被调用来创建该类型的新对象，因为它是可调用的。因此，要创建一个BasicStats对象，可以将该类型作为函数进行调用：

PyObject* myClassInstance = PyObject_CallFunctionObjArgs(myPyClass, NULL);

- md5i

---

文档中说PyInstanceMethod_New创建一个函数，这就解释了为什么它不起作用，因为它实际上并没有创建一个实例。 - user253751

Answer 2

我相信

PyObject* myClassInstance = PyInstanceMethod_New(MyPyClass);

真的应该是这样

// should call __init__. assumes __init__() has arity of 1
// otherwise you will have to marshall correct arguments
PyObject* myClassInstance = PyObject_CallObject(MyPyClass, 0);

- J Evans