在类体内调用类staticmethod？ [英] Calling class staticmethod within the class body?

问题描述

当我尝试从类主体中使用静态方法，并使用内置的 staticmethod 函数作为装饰器来定义静态方法时，如下所示：

When I attempt to use a static method from within the body of the class, and define the static method using the built-in staticmethod function as a decorator, like this:

class Klass(object):

    @staticmethod  # use as decorator
    def _stat_func():
        return 42

    _ANS = _stat_func()  # call the staticmethod

    def method(self):
        ret = Klass._stat_func() + Klass._ANS
        return ret

我收到以下错误：

Traceback (most recent call last):<br>
  File "call_staticmethod.py", line 1, in <module>
    class Klass(object): 
  File "call_staticmethod.py", line 7, in Klass
    _ANS = _stat_func() 
  TypeError: 'staticmethod' object is not callable

我了解为什么会这样（描述符绑定），并且可以解决该问题在上次使用后将 _stat_func（）手动转换为静态方法，例如：

I understand why this is happening (descriptor binding), and can work around it by manually converting _stat_func() into a staticmethod after its last use, like so:

class Klass(object):

    def _stat_func():
        return 42

    _ANS = _stat_func()  # use the non-staticmethod version

    _stat_func = staticmethod(_stat_func)  # convert function to a static method

    def method(self):
        ret = Klass._stat_func() + Klass._ANS
        return ret

所以我的问题是：

有没有更好的方法（如更清洁或更 Pythonic的方法）？

Are there better, as in cleaner or more "Pythonic", ways to accomplish this?

推荐答案

staticmeth od 对象显然具有 __ func __ 属性，该属性存储原始的原始函数（必须这样做）。这样就可以了：

staticmethod objects apparently have a __func__ attribute storing the original raw function (makes sense that they had to). So this will work:

class Klass(object):

    @staticmethod  # use as decorator
    def stat_func():
        return 42

    _ANS = stat_func.__func__()  # call the staticmethod

    def method(self):
        ret = Klass.stat_func()
        return ret

---

顺便说一句，尽管我怀疑静态方法对象具有某种存储原始功能的属性，但我不知道具体细节。本着教别人钓鱼而不是给他们钓鱼的精神，这就是我所做的调查，并发现了这一点（Python会话中的C& P）：

---

As an aside, though I suspected that a staticmethod object had some sort of attribute storing the original function, I had no idea of the specifics. In the spirit of teaching someone to fish rather than giving them a fish, this is what I did to investigate and find that out (a C&P from my Python session):

>>> class Foo(object):
...     @staticmethod
...     def foo():
...         return 3
...     global z
...     z = foo

>>> z
<staticmethod object at 0x0000000002E40558>
>>> Foo.foo
<function foo at 0x0000000002E3CBA8>
>>> dir(z)
['__class__', '__delattr__', '__doc__', '__format__', '__func__', '__get__', '__getattribute__', '__hash__', '__init__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']
>>> z.__func__
<function foo at 0x0000000002E3CBA8>

在交互式会话中进行类似的挖掘（ dir 非常有帮助）通常可以很快解决此类问题。

Similar sorts of digging in an interactive session (dir is very helpful) can often solve these sorts of question very quickly.

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