#class instance 初始化方法
def __myinit__(self,arg):print("__myinit__")self.arg=argdef classmethod1(self):print(self.arg)#class object's dict
attrs = {'__init__': __myinit__, 'classmethod1': classmethod1}
#基类
bases=(object,)ClassObject=type("ClassObject",bases,attrs)classInstance=ClassObject("abcde")
classInstance.classmethod1()

class MyMetaclass(type):def __new__(clz,name,bases,attrs):print("create new class ",name)return type.__new__(clz, name, bases, attrs)class UseMetaclass(object):__metaclass__=MyMetaclassdef __init__(self, arg):super(UseMetaclass, self).__init__()self.arg = argprint type(UseMetaclass)
#<class 'A.MyMetaclass'>

static PyObject *
build_class(PyObject *methods, PyObject *bases, PyObject *name)
{PyObject *metaclass = NULL, *result, *base;//检查属性是否已经填了__metaclass__if (PyDict_Check(methods))metaclass = PyDict_GetItemString(methods, "__metaclass__");if (metaclass != NULL){/*print_obj(metaclass);printf("\n");*/Py_INCREF(metaclass);}else if (PyTuple_Check(bases) && PyTuple_GET_SIZE(bases) > 0) {//从第一个基类里找__metaclass__,就是第一个基类的ob_type了,base 一般会是object 就是 那个PyBaseObject_Type，所以base.ob_type 就是PyType_Type ，这个class 对象就是 metaclass了// object.__class__==<type 'type'>base = PyTuple_GET_ITEM(bases, 0);metaclass = PyObject_GetAttrString(base, "__class__");if (metaclass == NULL) {PyErr_Clear();metaclass = (PyObject *)base->ob_type;Py_INCREF(metaclass);}//print_obj(metaclass);}else {// 这个else 处理 classic 的类定义方式 PyObject *g = PyEval_GetGlobals();if (g != NULL && PyDict_Check(g))metaclass = PyDict_GetItemString(g, "__metaclass__");if (metaclass == NULL)metaclass = (PyObject *) &PyClass_Type;Py_INCREF(metaclass);}//以上代码都为弄到一个__metaclass__/*创建一个类型对象， 调用metaclass ,会调用到 metaclass的 tp_call ,然后 还会调用到 type_new 创建一个新的类型对象,metaclass 是一个callable的对象*/result = PyObject_CallFunctionObjArgs(metaclass, name, bases, methods,NULL);Py_DECREF(metaclass);if (result == NULL && PyErr_ExceptionMatches(PyExc_TypeError)) {/* A type error here likely means that the user passedin a base that was not a class (such the random moduleinstead of the random.random type).  Help them out withby augmenting the error message with more information.*/PyObject *ptype, *pvalue, *ptraceback;PyErr_Fetch(&ptype, &pvalue, &ptraceback);if (PyString_Check(pvalue)) {PyObject *newmsg;newmsg = PyString_FromFormat("Error when calling the metaclass bases\n""    %s",PyString_AS_STRING(pvalue));if (newmsg != NULL) {Py_DECREF(pvalue);pvalue = newmsg;}}PyErr_Restore(ptype, pvalue, ptraceback);}return result;
}