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177 lines
2.2 KiB
Markdown
177 lines
2.2 KiB
Markdown
# 多重继承
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多重继承，指的是一个类别可以同时从多于一个父类继承行为与特征的功能，`Python` 是支持多重继承的：
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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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class ColorChangingLeaf(Leaf):
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def change(self, new_color='brown'):
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self.color = new_color
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class DeciduousLeaf(Leaf):
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def fall(self):
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print "Plunk!"
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class MapleLeaf(ColorChangingLeaf, DeciduousLeaf):
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pass
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```
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在上面的例子中， `MapleLeaf` 就使用了多重继承，它可以使用两个父类的方法：
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In [2]:
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```py
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leaf = MapleLeaf()
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leaf.change("yellow")
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print leaf.color
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leaf.fall()
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```
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```py
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yellow
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Plunk!
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```
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如果同时实现了不同的接口，那么，最后使用的方法以继承的顺序为准，放在前面的优先继承：
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In [3]:
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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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class ColorChangingLeaf(Leaf):
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def change(self, new_color='brown'):
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self.color = new_color
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def fall(self):
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print "Spalt!"
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class DeciduousLeaf(Leaf):
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def fall(self):
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print "Plunk!"
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class MapleLeaf(ColorChangingLeaf, DeciduousLeaf):
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pass
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```
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In [4]:
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```py
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leaf = MapleLeaf()
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leaf.fall()
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```
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```py
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Spalt!
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```
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In [5]:
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```py
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class MapleLeaf(DeciduousLeaf, ColorChangingLeaf):
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pass
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```
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In [6]:
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```py
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leaf = MapleLeaf()
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leaf.fall()
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```
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```py
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Plunk!
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```
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事实上，这个顺序可以通过该类的 `__mro__` 属性或者 `mro()` 方法来查看：
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In [7]:
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```py
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MapleLeaf.__mro__
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```
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Out[7]:
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```py
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(__main__.MapleLeaf,
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__main__.DeciduousLeaf,
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__main__.ColorChangingLeaf,
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__main__.Leaf,
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object)
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```
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In [8]:
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```py
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MapleLeaf.mro()
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```
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Out[8]:
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```py
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[__main__.MapleLeaf,
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__main__.DeciduousLeaf,
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__main__.ColorChangingLeaf,
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__main__.Leaf,
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object]
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```
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考虑更复杂的例子：
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In [9]:
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```py
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class A(object):
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pass
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class B(A):
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pass
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class C(A):
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pass
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class C1(C):
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pass
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class B1(B):
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pass
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class D(B1, C):
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pass
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```
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调用顺序：
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In [10]:
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```py
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D.mro()
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```
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Out[10]:
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```py
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[__main__.D, __main__.B1, __main__.B, __main__.C, __main__.A, object]
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``` |