如何理解 Python 的 Descriptor？

有人可以解释一下python的Descriptor知识吗？

回复内容：

旧文搬运：

<span class="o">>>></span> <span class="k">class</span> <span class="nc">MyInt</span><span class="p">(</span><span class="nb">int</span><span class="p">):</span> 
<span class="o">...</span>     <span class="k">def</span> <span class="nf">square</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> 
<span class="o">...</span>             <span class="k">return</span> <span class="bp">self</span><span class="o">*</span><span class="bp">self</span> 
<span class="o">...</span>      
<span class="o">>>></span> <span class="n">n</span> <span class="o">=</span> <span class="n">MyInt</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span> 
<span class="o">>>></span> <span class="n">n</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="s">'two'</span> 
<span class="o">>>></span> <span class="n">n</span><span class="o">.</span><span class="n">square</span><span class="p">()</span> 
<span class="mi">4</span> 
<span class="o">>>></span> <span class="n">n</span><span class="o">.</span><span class="n">name</span> 
<span class="s">'two'</span> 

简单来讲，描述符就是一个Python对象，但这个对象比较特殊，特殊性在于其属性的访问方式不再像普通对象那样访问，它通过一种叫描述符协议的方法来访问。这些方法包括__get__、__set__、__delete__。定义了其中任意一个方法的对象都叫描述符。举个例子：

普通对象

<span class="x">class Parent(object):</span>
<span class="x">    name = 'p'</span>

<span class="x">class Person(Parent):</span>
<span class="x">    name = "zs"</span>

<span class="x">zhangsan = Person()</span>
<span class="x">zhangsan.name = "zhangsan"</span>
<span class="x">print zhangsan.name</span>
<span class="x">#>> zhangsan</span>

以为是Python3.4里新加的什么牛逼功能，还和单继承联系起来了。吓得我赶紧翻了一下文档。

Descriptor就是一类实现了__get__(), __set__(), __delete__()方法的对象。没了。就这样了。没看懂的话去学习一下duck typing。

用途就很多了。把函数包装成property，把property包装成private property等等。 图片python装饰器语法,foo函数被装饰后,不再是原函数,
@logger是foo=logger(foo) 的语法糖,
foo是logger(foo)的返回值inner,inner是一个函数,foo(5)
等于inner(5).inner函数的形式参数是可变长度参数*args,**kwargs,
随便你传元组形式或字典形式的数据都可以。

两篇拙文，入门级水平

简明Python魔法-1
简明Python魔法-2

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