为什么super()不能使用除__new__之外的静态方法？

Question

我理解这__new__是一个静态方法,super()可以从它调用创建一个新对象,如下所示:

>>> class A:
...     def __new__(cls):
...         print('__new__ called')
...         return super().__new__(cls)
...
>>> a = A()
__new__ called

为什么super调用不能与其他静态方法一起使用？为什么以下失败？

>>> class B:
...     @staticmethod
...     def funcB():
...         print('funcB called')
...
>>> class C(B):
...     @staticmethod
...     def funcC():
...         print('funcC called')
...         super().funcB()
...
>>> c = C()
>>> c.funcC()
funcC called
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 5, in funcC
RuntimeError: super(): no arguments

Answer 1

super() 在Python 3中没有参数基本上是对其基于参数的版本的破解.

当super()没有参数时,它获取第一个参数,即使用名为的特殊单元变量的类__class__,对于第二个参数,它将从堆栈中获取第一个局部变量(这将是函数的第一个参数).

如果__new__它可以得到(__class__和cls)并且工作正常.

但在这种情况下,例如除了__class__它之外没有第二个变量,因此它失败了.

class A:
  @staticmethod
  def func():
    super().func()  # super(__class__, <missing>).func()


A().func()  # RuntimeError: super(): no arguments

现在,如果我们改变它以接受一个参数,那么事情会改变:

class A:
  @staticmethod
  def func(foo):
    super().func()


# This fails because super(B, 1).func() doesn't make sense.
A().func(1)  # TypeError: super(type, obj): obj must be an instance or subtype of type
# Works! But as there's no parent to this class with func() it fails as expected.
A().func(A())  # AttributeError: 'super' object has no attribute 'func'

因此,唯一的解决方案是super()在您的情况下使事情明确:

super(C, C).funcC()

一般来说,我不确定为什么静态方法的实现不能成为异常并且使用__class__两个参数来使其工作.

相关的CPython代码:

static int
super_init(PyObject *self, PyObject *args, PyObject *kwds)
{
    superobject *su = (superobject *)self;
    PyTypeObject *type = NULL;
    PyObject *obj = NULL;
    PyTypeObject *obj_type = NULL;

    if (!_PyArg_NoKeywords("super", kwds))
        return -1;
    if (!PyArg_ParseTuple(args, "|O!O:super", &PyType_Type, &type, &obj))
        return -1;

    if (type == NULL) {
        /* Call super(), without args -- fill in from __class__
           and first local variable on the stack. */
        PyFrameObject *f;
        PyCodeObject *co;
        Py_ssize_t i, n;
        f = PyThreadState_GET()->frame;
        if (f == NULL) {
            PyErr_SetString(PyExc_RuntimeError,
                            "super(): no current frame");
            return -1;
        }
        co = f->f_code;
        if (co == NULL) {
            PyErr_SetString(PyExc_RuntimeError,
                            "super(): no code object");
            return -1;
        }
        if (co->co_argcount == 0) {
            PyErr_SetString(PyExc_RuntimeError,
                            "super(): no arguments");
            return -1;
        }
        ...