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151 lines
2.0 KiB
Markdown
151 lines
2.0 KiB
Markdown
# 继承
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一个类定义的基本形式如下：
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```py
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class ClassName(ParentClass):
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"""class docstring"""
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def method(self):
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return
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```
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* `class` 关键词在最前面
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* `ClassName` 通常采用 `CamelCase` 记法
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* 括号中的 `ParentClass` 用来表示继承关系
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* 冒号不能缺少
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* `""""""` 中的内容表示 `docstring`，可以省略
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* 方法定义与函数定义十分类似，不过多了一个 `self` 参数表示这个对象本身
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* `class` 中的方法要进行缩进
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在里面有一个 `ParentClass` 项，用来进行继承，被继承的类是父类，定义的这个类是子类。 对于子类来说，继承意味着它可以使用所有父类的方法和属性，同时还可以定义自己特殊的方法和属性。
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假设我们有这样一个父类：
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In [1]:
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```py
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class Leaf(object):
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def __init__(self, color="green"):
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self.color = color
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def fall(self):
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print "Splat!"
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```
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测试：
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In [2]:
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```py
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leaf = Leaf()
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print leaf.color
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```
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```py
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green
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```
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In [3]:
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```py
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leaf.fall()
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```
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```py
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Splat!
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```
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现在定义一个子类，继承自 `Leaf`：
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In [4]:
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```py
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class MapleLeaf(Leaf):
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def change_color(self):
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if self.color == "green":
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self.color = "red"
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```
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继承父类的所有方法：
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In [5]:
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```py
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mleaf = MapleLeaf()
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print mleaf.color
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```
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```py
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green
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```
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In [6]:
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```py
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mleaf.fall()
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```
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```py
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Splat!
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```
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但是有自己独有的方法，父类中没有：
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In [7]:
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```py
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mleaf.change_color()
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print mleaf.color
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```
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```py
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red
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```
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如果想对父类的方法进行修改，只需要在子类中重定义这个类即可：
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In [8]:
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```py
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class MapleLeaf(Leaf):
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def change_color(self):
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if self.color == "green":
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self.color = "red"
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def fall(self):
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self.change_color()
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print "Plunk!"
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```
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In [9]:
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```py
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mleaf = MapleLeaf()
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print mleaf.color
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mleaf.fall()
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print mleaf.color
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```
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```py
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green
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Plunk!
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red
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``` |