08.13 多重继承
多重继承
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：
1class Leaf(object):
2 def __init__(self, color='green'):
3 self.color = color
4
5class ColorChangingLeaf(Leaf):
6 def change(self, new_color='brown'):
7 self.color = new_color
8
9class DeciduousLeaf(Leaf):
10 def fall(self):
11 print "Plunk!"
12
13class MapleLeaf(ColorChangingLeaf, DeciduousLeaf):
14 pass
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：
1leaf = MapleLeaf()
2
3leaf.change("yellow")
4print leaf.color
5
6leaf.fall()
yellow
Plunk!
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：
1class Leaf(object):
2 def __init__(self, color='green'):
3 self.color = color
4
5class ColorChangingLeaf(Leaf):
6 def change(self, new_color='brown'):
7 self.color = new_color
8 def fall(self):
9 print "Spalt!"
10
11class DeciduousLeaf(Leaf):
12 def fall(self):
13 print "Plunk!"
14
15class MapleLeaf(ColorChangingLeaf, DeciduousLeaf):
16 pass
1leaf = MapleLeaf()
2leaf.fall()
Spalt!
1class MapleLeaf(DeciduousLeaf, ColorChangingLeaf):
2 pass
1leaf = MapleLeaf()
2leaf.fall()
Plunk!
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：
1MapleLeaf.__mro__
(__main__.MapleLeaf,
__main__.DeciduousLeaf,
__main__.ColorChangingLeaf,
__main__.Leaf,
object)
1MapleLeaf.mro()
[__main__.MapleLeaf,
__main__.DeciduousLeaf,
__main__.ColorChangingLeaf,
__main__.Leaf,
object]
考虑更复杂的例子：
1class A(object):
2 pass
3
4class B(A):
5 pass
6
7class C(A):
8 pass
9
10class C1(C):
11 pass
12
13class B1(B):
14 pass
15
16class D(B1, C):
17 pass
调用顺序：
1D.mro()
[__main__.D, __main__.B1, __main__.B, __main__.C, __main__.A, object]