关键源码

LOAD_BUILD_CLASS

LOAD_BUILD_CLASS 这个字节码很特殊，从 Python/ceval.c 源码可以发现他的作用很简单，只是将 __build_class__​这个内建函数加载进栈顶。该函数为 builtins 模块中的一员，是一个负责创建类的工具函数。

        TARGET(LOAD_BUILD_CLASS) {
            _Py_IDENTIFIER(__build_class__);

            PyObject *bc;
            if (PyDict_CheckExact(f->f_builtins)) {
                bc = _PyDict_GetItemId(f->f_builtins, &PyId___build_class__);
                if (bc == NULL) {
                    PyErr_SetString(PyExc_NameError,
                                    "__build_class__ not found");
                    goto error;
                }
                Py_INCREF(bc);
            }
            else {
                PyObject *build_class_str = _PyUnicode_FromId(&PyId___build_class__);
                if (build_class_str == NULL)
                    goto error;
                bc = PyObject_GetItem(f->f_builtins, build_class_str);
                if (bc == NULL) {
                    if (PyErr_ExceptionMatches(PyExc_KeyError))
                        PyErr_SetString(PyExc_NameError,
                                        "__build_class__ not found");
                    goto error;
                }
            }
            PUSH(bc);
            DISPATCH();
        }

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__build_class__​

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LOAD_METHOD

        TARGET(LOAD_METHOD) {
            /* Designed to work in tamdem with CALL_METHOD. */
            PyObject *name = GETITEM(names, oparg);
            PyObject *obj = TOP();
            PyObject *meth = NULL;

            int meth_found = _PyObject_GetMethod(obj, name, &meth);

            if (meth == NULL) {
                /* Most likely attribute wasn't found. */
                goto error;
            }

            if (meth_found) {
                /* We can bypass temporary bound method object.
                   meth is unbound method and obj is self.

                   meth | self | arg1 | ... | argN
                 */
                SET_TOP(meth);
                PUSH(obj);  // self
            }
            else {
                /* meth is not an unbound method (but a regular attr, or
                   something was returned by a descriptor protocol).  Set
                   the second element of the stack to NULL, to signal
                   CALL_METHOD that it's not a method call.

                   NULL | meth | arg1 | ... | argN
                */
                SET_TOP(NULL);
                Py_DECREF(obj);
                PUSH(meth);
            }
            DISPATCH();
        }

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LOAD_ATTR

        TARGET(LOAD_ATTR) {
            PyObject *name = GETITEM(names, oparg);
            PyObject *owner = TOP();
            PyObject *res = PyObject_GetAttr(owner, name);
            Py_DECREF(owner);
            SET_TOP(res);
            if (res == NULL)
                goto error;
            DISPATCH();
        }

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_PyObject_GetMethod

int
_PyObject_GetMethod(PyObject *obj, PyObject *name, PyObject **method)
{
    PyTypeObject *tp = Py_TYPE(obj);
    PyObject *descr;
    descrgetfunc f = NULL;
    PyObject **dictptr, *dict;
    PyObject *attr;
    int meth_found = 0;

    assert(*method == NULL);

    if (Py_TYPE(obj)->tp_getattro != PyObject_GenericGetAttr
            || !PyUnicode_Check(name)) {
        *method = PyObject_GetAttr(obj, name);
        return 0;
    }

    if (tp->tp_dict == NULL && PyType_Ready(tp) < 0)
        return 0;

    descr = _PyType_Lookup(tp, name);
    if (descr != NULL) {
        Py_INCREF(descr);
        if (PyFunction_Check(descr) ||
                (Py_TYPE(descr) == &PyMethodDescr_Type)) {
            meth_found = 1;
        } else {
            f = descr->ob_type->tp_descr_get;
            if (f != NULL && PyDescr_IsData(descr)) {
                *method = f(descr, obj, (PyObject *)obj->ob_type);
                Py_DECREF(descr);
                return 0;
            }
        }
    }

    dictptr = _PyObject_GetDictPtr(obj);
    if (dictptr != NULL && (dict = *dictptr) != NULL) {
        Py_INCREF(dict);
        attr = PyDict_GetItem(dict, name);
        if (attr != NULL) {
            Py_INCREF(attr);
            *method = attr;
            Py_DECREF(dict);
            Py_XDECREF(descr);
            return 0;
        }
        Py_DECREF(dict);
    }

    if (meth_found) {
        *method = descr;
        return 1;
    }

    if (f != NULL) {
        *method = f(descr, obj, (PyObject *)Py_TYPE(obj));
        Py_DECREF(descr);
        return 0;
    }

    if (descr != NULL) {
        *method = descr;
        return 0;
    }

    PyErr_Format(PyExc_AttributeError,
                 "'%.50s' object has no attribute '%U'",
                 tp->tp_name, name);
    return 0;
}

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PyObject_GetAttr

PyObject *
PyObject_GetAttr(PyObject *v, PyObject *name)
{
    PyTypeObject *tp = Py_TYPE(v);

    if (!PyUnicode_Check(name)) {
        PyErr_Format(PyExc_TypeError,
                     "attribute name must be string, not '%.200s'",
                     name->ob_type->tp_name);
        return NULL;
    }
    if (tp->tp_getattro != NULL)
        return (*tp->tp_getattro)(v, name);
    if (tp->tp_getattr != NULL) {
        const char *name_str = PyUnicode_AsUTF8(name);
        if (name_str == NULL)
            return NULL;
        return (*tp->tp_getattr)(v, (char *)name_str);
    }
    PyErr_Format(PyExc_AttributeError,
                 "'%.50s' object has no attribute '%U'",
                 tp->tp_name, name);
    return NULL;
}