CODEWITHSUNDEEP
python
user10870615
user10870615

Reputation:

Why does __new__ not have classmethod decorator

Why doesn't the new method have a class decorator on it? For example:

class MyClass:
    @classmethod
    def __new__(cls, *args, **kwargs):
        pass

How is this method able to act as a classmethod without having that decorator on it?

Upvotes: 7

Views: 456

Answers (1)

user2357112
user2357112

Reputation: 281287

It's specifically special-cased. type.__new__ will apply staticmethod automatically when creating your class if it sees that you defined a __new__ without applying staticmethod. (Also, __new__ is supposed to be a staticmethod, not a classmethod.)

See the docs:

Called to create a new instance of class cls. __new__() is a static method (special-cased so you need not declare it as such) that takes the class of which an instance was requested as its first argument...

and the implementation:

    /* Special-case __new__: if it's a plain function,
       make it a static function */
    tmp = _PyDict_GetItemId(dict, &PyId___new__);
    if (tmp != NULL && PyFunction_Check(tmp)) {
        tmp = PyStaticMethod_New(tmp);
        if (tmp == NULL)
            goto error;
        if (_PyDict_SetItemId(dict, &PyId___new__, tmp) < 0) {
            Py_DECREF(tmp);
            goto error;
        }
        Py_DECREF(tmp);
    }

Upvotes: 8

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