Python3 - using super() in eq methods raises RuntimeError: super(): class cell not found

Question

我正在修补 class 的 __eq__ 方法。我发现以下工作：

   def eq(obj, other):
       if isinstance(other, str):
          return obj.name.upper() == other.upper()
       else:
          return object.__eq__(obj, other)

这不起作用：

  def eq(obj, other):
     if isinstance(other, str):
         return obj.name.upper() == other.upper()
     else:
        return super().__eq__(other)

这有时有效，但有时会引发错误：

def eq(obj, other):
   if isinstance(other, str):
       return obj.name.upper() == other.upper()
   else:
       return super().__eq__(self, other)

错误：

<ipython-input-128-91287536205d> in eq(obj, other)
      3         return obj.name.upper() == other.upper()
      4     else:
----> 5         return super().__eq__(self, other)
      6 
      7 

RuntimeError: super(): __class__ cell not found

你能解释一下这是怎么回事吗？如何将 object 正确替换为 super()？

Answer 1

您不能在 class 之外定义的函数中使用不带参数的 super()。 __class__ 单元 super() 所依赖的仅提供给 class 主体中定义的函数。来自 super() documentation:

The zero argument form only works inside a class definition, as the compiler fills in the necessary details to correctly retrieve the class being defined, as well as accessing the current instance for ordinary methods.

使用双参数形式，明确命名 class：

def eq(obj, other):
   if isinstance(other, str):
       return obj.name.upper() == other.upper()
   else:
       return super(ClassYouPutThisOn, obj).__eq__(other)

ClassYouPutThisOn.__eq__ = eq

这需要您在 monkey 补丁中明确命名 class，从而降低其重用性。

相反，您可以通过将 eq 嵌套在另一个以 __class__ 作为本地名称的函数中，手动 提供所需的 __class__ 单元格 ：

def patch_eq(cls):
    __class__ = cls  # provide closure cell for super()
    def eq(obj, other):
       if isinstance(other, str):
           return obj.name.upper() == other.upper()
       else:
           return super().__eq__(other)
    cls.__eq__ = eq

super() 通过从调用帧中获取第一个本地名称（即传递给函数调用的第一个参数，通常称为 self）找到第二个参数（对实例的引用） .

另见 Why is Python 3.x's super() magic?

使用嵌套函数方法的演示：

>>> class Foo:
...     name = 'bar'
...     def __eq__(self, other):
...         return False
...
>>> Foo() == 'Bar'
False
>>> Foo() == Foo()
False
>>> patch_eq(Foo)
>>> Foo() == 'Bar'
True
>>> Foo() == Foo()
False

Python3 - using super() in eq methods raises RuntimeError: super(): class cell not found

Python3 - using super() in eq methods raises RuntimeError: super(): class cell not found

python

overloading

monkeypatching

super

python-3.x

Python3 - using super() in __eq__ methods raises RuntimeError: super(): __class__ cell not found

Python3 - using super() in __eq__ methods raises RuntimeError: super(): __class__ cell not found

python

overloading

monkeypatching

super

python-3.x

Python3 - using super() in eq methods raises RuntimeError: super(): class cell not found

Python3 - using super() in eq methods raises RuntimeError: super(): class cell not found