python内置函数2-classmethod()

693579551

　　Help on>
　　class>　　|  classmethod(function) -> method
　　|

　　|  Convert a function to be a>　　|

　　|  A>　　|  just like an instance method receives the instance.

　　|  To declare a>　　|
　　|    class C:
　　|        def f(cls, arg1, arg2, ...): ...

　　|        f =>　　|

　　|  It can be called either on the>
　　|  (e.g. C().f()).  The instance is ignored except for its>
　　|  If a>　　|  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__(...)
　　|      descr.__get__(obj[, type]) -> value
　　|
　　|  __getattribute__(...)
　　|      x.__getattribute__('name') <==> x.name
　　|
　　|  __init__(...)
　　|      x.__init__(...) initializes x; see help(type(x)) for signature
　　|
　　|  ----------------------------------------------------------------------
　　|  Data descriptors defined here:
　　|
　　|  __func__
　　|
　　|  ----------------------------------------------------------------------
　　|  Data and other attributes defined here:
　　|
　　|  __new__ = <built-in method __new__ of type object>
　　|      T.__new__(S, ...) -> a new object with type S, a subtype of T
　　classmethod(function)

　　Return a>
　　A>　　class C(object):
　　@classmethod
　　def f(cls, arg1, arg2, ...):
　　...
　　The @classmethod form is a function decorator – see the description of function definitions in Function definitions for details.

　　It can be called either on the>　　Class methods are different than C++ or Java static methods. If you want those, see staticmethod() in this section.

　　For more information on>　　Changed in version 2.4: Function decorator syntax added.
　　中文说明：
　　classmethod是用来指定一个类的方法为类方法，没有此参数指定的类的方法为实例方法，使用方法如下：
　　class C:
　　@classmethod
　　def f(cls, arg1, arg2, ...): ...
　　类方法既可以直接类调用(C.f())，也可以进行实例调用(C().f())。

　　>>>>　　...     @classmethod
　　...     def f(self):

　　...         print "This is a>　　...
　　>>> C.f()

　　This is a>　　>>> c=C()
　　>>> c.f()

　　This is a>
　　>>>>　　...     def f(self):

　　...         print "This is not a>　　...
　　>>> D.f()
　　Traceback (most recent call last):
　　File "<stdin>", line 1, in <module>
　　TypeError: unbound method f() must be called with D instance as first argument (got nothing instead)
　　>>> d=D()
　　>>> d.f()

　　This is not a>