写在前面

本节总结了python中类的继承。类的一般继承和super(), 两者的对比。

一般继承

class Base(object):
    def __init__(self):
        self._a = 0
        self._b = 0
        print 'enter base'
        print 'leave base'

    def a(self):
        return self._a

    def b(self):
        return self._b

    def aa(self):
        c = self.a() + self.b()
        return c


class childA(Base):
    def __init__(self):
        self._c = 1
        print 'enter childA'
        Base.__init__(self)
        print 'leave childA'

    def c(self):
        return self._c

    def aa(self):
        d = self.a() + self.b() + self.c() + b
        return d


class childB(Base):
    def __init__(self):
        print 'enter childB'
        Base.__init__(self)
        print 'leave childB'


class childC(Base):
    def __init__(self):
        print 'enter childC'
        Base.__init__(self)
        print 'leave childC'


class childD(childB, childC, childA):
    def __init__(self):
        print 'enter childD'
        childB.__init__(self)
        childC.__init__(self)
        childA.__init__(self)
        print 'leave childD'


childD()

输出：

enter childD
enter childB
enter base
leave base
leave childB
enter childC
enter base
leave base
leave childC
enter childA
enter base
leave base
leave childA
leave childD

super()继承

class Base(object):
    def __init__(self):
        self._a = 0
        self._b = 0
        print 'enter base'
        print 'leave base'

    def a(self):
        return self._a

    def b(self):
        return self._b

    def aa(self):
        c = self.a() + self.b()
        return c


class childA(Base):
    def __init__(self):
        self._c = 1
        print 'enter childA'
        super(childA, self).__init__()
        print 'leave childA'

    def c(self):
        return self._c

    def aa(self):
        d = self.a() + self.b() + self.c() + b
        return d


class childB(Base):
    def __init__(self):
        print 'enter childB'
        super(childB, self).__init__()
        print 'leave childB'


class childC(Base):
    def __init__(self):
        print 'enter childC'
        super(childC, self).__init__()
        print 'leave childC'


class childD(childB, childC, childA):
    def __init__(self):
        print 'enter childD'
        super(childD, self).__init__()
        print 'leave childD'

childD()

输出：

enter childD
enter childB
enter childC
enter childA
enter base
leave base
leave childA
leave childC
leave childB
leave childD

首先对比两者的代码，当我需要修改基类的名字的时候，普通的继承方式中则需要修改很多地方，无疑增加了代码量。另外，python在使用多继承的时候要多次重复的写继承方式，显得很累赘。

因此，python提供了一种方法super(). 尤其在多继承情况下，对比上面两段代码的输出，发现基类Base()调用的次数不一样。具体机制见参考文献。