8 python 定制自己的类，实现查看属性，按index取值，迭代，切片等个性化类

class="baidu_pl">

class="article_content clearfix">

class="markdown_views prism-atom-one-dark">

1 str

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Studentclass="hljs-params">(object):
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__init__class="hljs-params">(self,name):
        self.name = name
class="hljs-keyword">print Student(class="hljs-string">'Michael')

<__main__.Student object at 0x7fa939eda310>

怎么打印的好看呢？

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Studentclass="hljs-params">(object):
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__init__class="hljs-params">(self,name):
        self.name = name
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__str__class="hljs-params">(self):
        class="hljs-keyword">return class="hljs-string">'Student object (name:%s)'  % self.name
class="hljs-keyword">print Student(class="hljs-string">'huxiang')

Student object (name:huxiang)

上面说明print 调用的是str这个方法，对不对？
但是不用print 输出还是很难看，例如：

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">Student(class="hljs-string">'huxiang')

<__main__.Student at 0x7fa939eda250>

这是为什么呢？直接输出调用的是另一个方法了，改写如下

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Studentclass="hljs-params">(object):
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__init__class="hljs-params">(self,name):
        self.name = name
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__str__class="hljs-params">(self):
        class="hljs-keyword">return class="hljs-string">'Student object (name=%s)' % self.name
    __repr__ = __str__

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">Student(class="hljs-string">'HUXIANG')

Student object (name=HUXIANG)

说明直接输出也是调用一个方法，而这个方法是repr

class="tags" href="/tags/DieDai.html" title=迭代>迭代">2 iter 实现class="tags" href="/tags/DieDai.html" title=迭代>迭代

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Fibclass="hljs-params">(object):
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__init__class="hljs-params">(self):
        self.a,self.b = class="hljs-number">0,class="hljs-number">1 class="hljs-comment">#初始值
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__iter__class="hljs-params">(self):
        class="hljs-keyword">return self

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-keyword">for n class="hljs-keyword">in Fib():
    class="hljs-keyword">print n

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

TypeError                                 Traceback (most recent call last)

<iclass="tags" href="/tags/PYTHON.html" title=python>python-input-8-b601c92d0330> in <module>()
----> 1 for n in Fib():
      2     print n


TypeError: iter() returned non-iterator of type 'Fib'

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Fibclass="hljs-params">(object):
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__init__class="hljs-params">(self):
        self.a,self.b = class="hljs-number">0,class="hljs-number">1 class="hljs-comment">#初始值
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__iter__class="hljs-params">(self):
        class="hljs-keyword">return self
    class="hljs-function">class="hljs-keyword">def class="hljs-title">nextclass="hljs-params">(self):class="hljs-comment">#next是什么？也是class="tags" href="/tags/DieDai.html" title=迭代>迭代时要用到的吗？
        self.a,self.b = self.b,self.a+self.b class="hljs-comment">#下一轮class="tags" href="/tags/DieDai.html" title=迭代>迭代后的值
        class="hljs-keyword">if self.a>class="hljs-number">100000:
            class="hljs-keyword">raise StopIteration();
        class="hljs-keyword">return self.a

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-keyword">for n class="hljs-keyword">in Fib():
    class="hljs-keyword">print n

3 getitem用于取得第几个元素，所以改写这个方法就可以直接取某个元素了

例如这里没定义，直接去会报错

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">Fib()[class="hljs-number">5]

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

TypeError                                 Traceback (most recent call last)

<iclass="tags" href="/tags/PYTHON.html" title=python>python-input-11-f91ed6abd284> in <module>()
----> 1 Fib()[5]


TypeError: 'Fib' object does not support indexing

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Fibclass="hljs-params">(object):
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__getitem__class="hljs-params">(self,n):
        a,b = class="hljs-number">1, class="hljs-number">1
        class="hljs-keyword">for x class="hljs-keyword">in range(n):
            a, b = b, a + b
        class="hljs-keyword">return a

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">f = Fib()

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">f[class="hljs-number">5]

但是还不能切片，怎么实现切片呢？还是修改getitem这个方法，判断传入值的类型，然后再决定返回的类型

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Fibclass="hljs-params">(object):
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__getitem__class="hljs-params">(self,n):
        class="hljs-keyword">if isinstance(n,int):
            a, b = class="hljs-number">1, class="hljs-number">1
            class="hljs-keyword">for x class="hljs-keyword">in range(n):
                a, b = b, a + b
            class="hljs-keyword">return a
        class="hljs-keyword">if isinstance(n,slice):
            start = n.start
            stop = n.stop
            a, b = class="hljs-number">1, class="hljs-number">1
            L = []
            class="hljs-keyword">for x class="hljs-keyword">in range(stop):
                class="hljs-keyword">if x >= start:
                    L.append(a)
                a, b = b, a + b
            class="hljs-keyword">return L

  File "<iclass="tags" href="/tags/PYTHON.html" title=python>python-input-15-e90f9954e169>", line 6
    a, b = b, a　+ b
               ^
SyntaxError: invalid syntax

我靠我错在哪？

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Fibclass="hljs-params">(object):
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__getitem__class="hljs-params">(self, n):
        class="hljs-keyword">if isinstance(n, int):
            a, b = class="hljs-number">1, class="hljs-number">1
            class="hljs-keyword">for x class="hljs-keyword">in range(n):
                a, b = b, a + b
            class="hljs-keyword">return a
        class="hljs-keyword">if isinstance(n, slice):
            start = n.start
            stop = n.stop
            a, b = class="hljs-number">1, class="hljs-number">1
            L = []
            class="hljs-keyword">for x class="hljs-keyword">in range(stop):
                class="hljs-keyword">if x >= start:
                    L.append(a)
                a, b = b, a + b
            class="hljs-keyword">return L

下面就可以用切片了，爽！

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">f = Fib()

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">f[class="hljs-number">0:class="hljs-number">5]

[1, 1, 2, 3, 5]

总之，通过上面的方法，我们自己定义的类表现得和Python自带的list、tuple、dict没什么区别，这完全归功于动态语言的“鸭子类型”，不需要强制继承某个接口。

另外还有其他的　一些’内在方法’，例如：
Python解释器会试图调用getattr(self, ‘score’)来尝试获得属性，这样，我们就有机会返回score的值：

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Studentclass="hljs-params">(object):

    class="hljs-function">class="hljs-keyword">def class="hljs-title">__init__class="hljs-params">(self):
        self.name = class="hljs-string">'Michael'

    class="hljs-function">class="hljs-keyword">def class="hljs-title">__getattr__class="hljs-params">(self, attr):
        class="hljs-keyword">if attr==class="hljs-string">'score':
            class="hljs-keyword">return class="hljs-number">99

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">s = Student()
class="hljs-keyword">print s.name
class="hljs-keyword">print s.score

Michael
99

只需要定义一个call()方法，就可以直接对实例进行调用。请看示例：

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">class="hljs-class">class="hljs-keyword">class class="hljs-title">Studentclass="hljs-params">(object):
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__init__class="hljs-params">(self):
        self.name = class="hljs-string">'huxiang'
    class="hljs-function">class="hljs-keyword">def class="hljs-title">__call__class="hljs-params">(self):
        print(class="hljs-string">'My name is %s.' % self.name)

class="prettyprint">class="language-class="tags" href="/tags/PYTHON.html" title=python>python hljs ">s = Student()
s()

My name is huxiang.

小结

Python的class允许定义许多定制方法，可以让我们非常方便地生成特定的类。