Python中的method

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什么是method？

function就是可以通过名字可以调用的一段代码,我们可以传参数进去，得到返回值。所有的参数都是明确的传递过去的。
method是function与对象的结合。我们调用一个方法的时候，有些参数是隐含的传递过去的。下文会详细介绍。

In [5]: class Human(object):

...: def __init__(self, weight):

...: self.weight = weight

...: def get_weight(self):

...: return self.weight

...:

In [6]: Human.get_weight

Out[6]: <unbound method Human.get_weight>

这告诉我们get_weight是一个没有被绑定方法，什么叫做未绑定呢？继续看下去。

In [7]: Human.get_weight()

---------------------------------------------------------------------------

TypeError Traceback (most recent call last)

/home/yao/learn/insight_python/<ipython-input-7-a2b2c5cd2f8d> in <module>()

----> 1 Human.get_weight()

TypeError: unbound method get_weight() must be called with Human instance as first argument (got nothing instead)

未绑定的方法必须使用一个Human实例作为第一个参数来调用啊。那我们来试试

1 2	In [10]: Human.get_weight(Human(45)) Out[10]: 45

果然成功了，但是一般情况下我们习惯这么使用。

In [11]: person = Human(45)

In [12]: person.get_weight()

Out[12]: 45

这两种方式的结果一模一样。我们看下官方文档是怎么解释这种现象的。

When an instance attribute is referenced that isn’t a data attribute, its class is searched.

If the name denotes a valid class attribute that is a function object, a method object is

created by packing (pointers to) the instance object and the function object just found together

in an abstract object: this is the method object. When the method object is called with an

argument list, a new argument list is constructed from the instance object and the argument list,

and the function object is called with this new argument list.

原来我们常用的调用方法(person.get_weight())是把调用的实例隐藏的作为一个参数self传递过去了, self 只是一个普通的参数名称,不是关键字。