关于python类中super()和__init__()的区别说明

class Base(object):
    def init(self):
        print 'Base create'
class childA(Base):
    def init(self):
        print 'creat A ',
        Base.init(self)
class childB(Base):
    def init(self):
        print 'creat B ',
        super(childB, self).init()
base = Base()
a = childA()
b = childB() 

输出结果：

Base create
creat A  Base create
creat B  Base create 

super()只能用于新式类中

把基类改为旧式类，即不继承任何基类

class Base():
    def init(self):
        print 'Base create' 

执行时，在初始化b时就会报错：

super(childB, self).init()
TypeError: must be type, not classobj 

super不是父类，而是继承顺序的下一个类

在多重继承时会涉及继承顺序，super（）相当于返回继承顺序的下一个类，而不是父类，类似于这样的功能：

def super(class_name, self):
    mro = self.class.mro()
    return mro[mro.index(class_name) + 1] 

mro()用来获得类的继承顺序。 例如：

class Base(object):
    def init(self):
        print 'Base create'
class childA(Base):
    def init(self):
        print 'enter A '
        # Base.init(self)
        super(childA, self).init()
        print 'leave A'
class childB(Base):
    def init(self):
        print 'enter B '
        # Base.init(self)
        super(childB, self).init()
        print 'leave B'
class childC(childA, childB):
    pass
c = childC()
print c.class.mro 

输出结果如下：

enter A 
enter B 
Base create
leave B
leave A
(<class 'main.childC'>, <class 'main.childA'>, <class 'main.childB'>, <class 'main.Base'>, <type 'object'>) 

在多重继承里，如果把childA()中的 super(childA, self).init() 换成Base._init_(self)，在执行时，继承childA后就会直接跳到Base类里，而略过了childB：

enter A 
Base create
leave A
(<class 'main.childC'>, <class 'main.childA'>, <class 'main.childB'>, <class 'main.Base'>, <type 'object'>) 

比如将childA()中的super改为：super(childC, self).init()，程序就会无限递归下去。 如：

  File "test.py", line 12, in init
    super(childC, self).init()
  File "test.py", line 12, in init
    super(childC, self).init()
  File "test.py", line 12, in init
    super(childC, self).init()
  File "test.py", line 12, in init
    super(childC, self).init()
  File "test.py", line 12, in init
    super(childC, self).init()
  File "test.py", line 12, in init
    super(childC, self).init()
  File "test.py", line 12, in init
    super(childC, self).init()
  File "test.py", line 12, in init
    super(childC, self).init()
  File "test.py", line 12, in init
    super(childC, self).init()
RuntimeError: maximum recursion depth exceeded while calling a Python object 

super()可以避免重复调用

如果childA基础Base, childB继承childA和Base，如果childB需要调用Base的init()方法时，就会导致init()被执行两次：

class Base(object):
    def init(self):
        print 'Base create'
class childA(Base):
    def init(self):
        print 'enter A '
        Base.init(self)
        print 'leave A'
class childB(childA, Base):
    def init(self):
        childA.init(self)
        Base.init(self)
b = childB() 

Base的init()方法被执行了两次

enter A 
Base create
leave A
Base create 

使用super()是可避免重复调用

class Base(object):
    def init(self):
        print 'Base create'
class childA(Base):
    def init(self):
        print 'enter A '
        super(childA, self).init()
        print 'leave A'
class childB(childA, Base):
    def init(self):
        super(childB, self).init()
b = childB()
print b.class.mro()
enter A 
Base create
leave A
[<class 'main.childB'>, <class 'main.childA'>, <class 'main.Base'>, <type 'object'>] 

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