python @classmethod 中的“self”指的是什么？
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What does 'self' refer to in a @classmethod?
提问by Yes - that Jake.
I thought I was starting to get a grip on "the Python way" of programming. Methods of a class accept self as the first parameter to refer to the instance of the class whose context the method is being called in. The @classmethod decorator refers to a method whose functionality is associated with the class, but which doesn't reference a specific instance.
我以为我开始掌握编程的“Python 方式”。类的方法接受 self 作为第一个参数来引用调用该方法的上下文的类的实例。@classmethod 装饰器引用一个方法，其功能与类相关联，但不引用具体实例。
So, what does the first parameter of a @classmethod (canonically 'self') refer to if the method is meant to be called without an instance reference?
那么，如果要在没有实例引用的情况下调用该方法，@classmethod（规范的“self”）的第一个参数指的是什么？
回答by SilentGhost
类本身：
A class method receives the class as implicit first argument, just like an instance method receives the instance.
类方法接收类作为隐式第一个参数，就像实例方法接收实例一样。
class C:
@classmethod
def f(cls):
print(cls.__name__, type(cls))
>>> C.f()
C <class 'type'>
and it's clscanonically, btw
这是cls规范的，顺便说一句
回答by Torsten Marek
The first parameter of a classmethod is named clsby convention and refers to the the class object on which the method it was invoked.
classmethod 的第一个参数按照cls约定命名，指的是调用它的方法所在的类对象。
>>> class A(object):
... @classmethod
... def m(cls):
... print cls is A
... print issubclass(cls, A)
>>> class B(A): pass
>>> a = A()
>>> a.m()
True
True
>>> b = B()
>>> b.m()
False
True
回答by boatcoder
Django does some strange stuff with a class method here:
Django 在这里用一个类方法做了一些奇怪的事情：
class BaseFormSet(StrAndUnicode):
"""
A collection of instances of the same Form class.
"""
def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
initial=None, error_class=ErrorList):
...
self.prefix = prefix or self.get_default_prefix()
...
Even though get_default_prefix is declared this way (in the same class):
即使 get_default_prefix 以这种方式声明（在同一个类中）：
@classmethod
def get_default_prefix(cls):
return 'form'
回答by Jason Baker
The class object gets passed as the first parameter. For example:
类对象作为第一个参数传递。例如：
class Foo(object):
@classmethod
def bar(self):
return self()
Would return an instance of the Foo class.
将返回 Foo 类的一个实例。
EDIT:
编辑：
Note that the last line would be self() not self. self would return the class itself, while self() returns an instance.
请注意，最后一行是 self() 而不是 self。self 将返回类本身，而 self() 返回一个实例。
