Question

以前我使用C API创建了一些Python类。当我要使用Python 3+构建旧项目时，它会产生以下编译错误

PyClass_New was not declared in this scope
Py_InitModule was not declared in this scope

等价物是什么？

PyObject *pClassDic = PyDict_New();
PyObject *pClassName = PyBytes_FromString("MyClass");
PyObject *pClass = PyClass_New(NULL, pClassDic, pClassName);

Answer 1

如果你不想经历设置对象和输入结构的麻烦，你应该能够通过从C调用Python的type(name, bases, dict)来创建一个新类：

PyObject *pClassName = PyBytes_FromString("MyClass");
PyObject *pClassBases = PyTuple_New(0); // An empty tuple for bases is equivalent to `(object,)`
PyObject *pClassDic = PyDict_New();

// pClass = type(pClassName, pClassBases, pClassDic)
PyObject *pClass = PyObject_CallFunctionObjArgs(PyType_Type, pClassName, pClassBases, pClassDic, NULL);

Py_CLEAR(pClassName);
Py_CLEAR(pClassBases);
Py_CLEAR(pClassDic);

Answer 2

从'cpburnz'完成答案，这是一个创建类对象并添加方法的函数：

PyObject *createClassObject(const char *name, PyMethodDef methods[])
{
    PyObject *pClassName = PyUnicode_FromString(name);
    PyObject *pClassBases = PyTuple_New(0); // An empty tuple for bases is equivalent to `(object,)`
    PyObject *pClassDic = PyDict_New();


    PyMethodDef *def;
    // add methods to class 
    for (def = methods; def->ml_name != NULL; def++)
    {
        printf("     add method %s\n", def->ml_name);
        PyObject *func = PyCFunction_New(def, NULL);
        PyObject *method = PyInstanceMethod_New(func);
        PyDict_SetItemString(pClassDic, def->ml_name, method);
        Py_DECREF(func);
        Py_DECREF(method);
    }

    // pClass = type(pClassName, pClassBases, pClassDic)
    PyObject *pClass = PyObject_CallFunctionObjArgs((PyObject *)&PyType_Type, pClassName, pClassBases, pClassDic, NULL);

    Py_DECREF(pClassName);
    Py_DECREF(pClassBases);
    Py_DECREF(pClassDic);


    return pClass;
}

然后，您可以像这样使用它：

static PyMethodDef foo_Methods[] =
{
    { "__init__", fooInit, METH_VARARGS, "doc" },
    { "do_something", fooDoSomething, METH_VARARGS, "doc" },
    { 0, 0 },
};

PyObject * fooClass = createClassObject("fooClass", foo_Methods);
PyModule_AddObject(module, "foo", fooClass );

请求PyModule_AddObject使python代码可以看到“foo”类。

注意：正如'RomanK'所建议的那样，使用PyTypeObject是一个很好的（可能更好）替代方案。

编辑：我确认直接使用PyTypeObject更好更容易，填充结构并调用PyModule_AddObject（）以使新类型可用于Python。它更灵活，提供更大的灵活性，这是官方的方式。正如Cilyan所提到的，这里解释了所有内容：https://docs.python.org/3.3/extending/newtypes.html?highlight=pytypeobject

什么是Python 3中的PyClass_New等价物？

2 个答案: