python __builtins__ classmethod类 （11）

11、'classmethod', 修饰符对应的函数不需要实例化，不需要 self 参数，但第一个参数需要是表示自身类的 cls 参数，可以来调用类的属性，类的方法，实例化对象等。

class classmethod(object)
 |  classmethod(function) -> method
 |
 |  Convert a function to be a class method.  # 将一个函数转换成类方法
 |
 |  A class method receives the class as implicit first argument,
    一个类方法，接收类作为隐式参数
 |  just like an instance method receives the instance.
    就像一个实例方法接收实例对象
 |  To declare a class method, use this idiom:
 |
 |    class C:
 |        @classmethod
 |        def f(cls, arg1, arg2, ...):
 |            ...
 |
 |  It can be called either on the class (e.g. C.f()) or on an instance
 |  (e.g. C().f()).  The instance is ignored except for its class.
    可以用类对象调用f函数，也可以实例对象调用f函数。
 |  If a class method is called for a derived class, the derived class
 |  object is passed as the implied first argument.
 |
 |  Class methods are different than C++ or Java static methods.
 |  If you want those, see the staticmethod builtin.
 |
 |  Methods defined here:
 |
 |  __get__(self, instance, owner, /)
 |      Return an attribute of instance, which is of type owner.
 |
 |  __init__(self, /, *args, **kwargs)
 |      Initialize self.  See help(type(self)) for accurate signature.
 |
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.
 |
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |
 |  __dict__
 |
 |  __func__
 |
 |  __isabstractmethod__