python语言与C++有相似的类继承,在类定义时,python中会自定义第一个self,类似C++中this指针,指向对象自身。
python简单的类举例:
>>> class hello(object): ... def print_c(): ... print"hello world!" >>> hello().print_c() hello world! 当然在实际中不可避免的需要类的继承,子类继承父类,正常如下: >>> class child(hello): ... def print_c(self): ... hello().print_c() ... >>> child().print_c() hello world! 在python中还提供了super()机制,例子如下: >>> class hello(object): ... def print_c(self): ... print"hello world!" ... >>> class child(hello): ... def print_c(self): ... super(child,self).print_c() ... >>> child().print_c() hello world! 第一眼看过来是不是感觉一样?在python中引入super()的目的是保证相同的基类只初始化一次(注意:
1super ()机制是用来解决多重继承的,对于直接调用父类名是没有问题的,但在之后根据前人的经验就是:要么都用类名调用,要么就全部用super(),不要混合的用,由此为人做事还是要专一的嘛O(∩_∩)O~
2 super()继承只能用于新式类,用于经典类时就会报错。 新式类:必须有继承的类,如果无继承的,则继承object 经典类:没有父类,如果此时调用super就会出现错误:『super() argument 1 must be type, not classobj)
好,再举一个例子
class parent1(object): def __init__(self): print 'is parent1' print 'goes parent1' class parent2(object): def __init__(self): print 'is parent2' print 'goes parent2' class child1(parent1): def __init__(self): print'is child1' parent.__init__(self) print 'goes child1' class child2 (parent1) : def __init__(self): print 'is child2' parent.__init__(self) print 'goes child2' class child3(parent2): def __init__(self): print 'is child3' parent2.__init__(self) print 'goes child3' class grandson(child3,child2,child1): def __init__(self): print 'is grandson' child1.__init__(self) child2.__init__(self) child3.__init__(self) print'goes grandson' if __name__=='__main__': grandson() is grandson is child1 is parent1 goes parent1 goes child1 is child2 is parent1 goes parent1 goes child2 is child3 is parent2 goes parent2 goes child3 goes grandson 好了,在这儿发现什么问题了没有?对,基类parent1被多次执行,而有时我们只希望公共的类只被执行一次,那么此时我们引入super()机制查看效果: <span style="font-family: Arial, Helvetica, sans-serif;">class parent1(object):</span> def __init__(self): super(parent1, self).__init__() print 'is parent1' print 'goes parent1' class parent2(object): def __init__(self): super(parent2, self).__init__() print 'is parent2' print 'goes parent2' class child1(parent1): def __init__(self): print'is child1' #parent1.__init__(self) super(child1, self).__init__() print 'goes child1' class child2 (parent1) : def __init__(self): print 'is child2' #parent1.__init__(self) super(child2, self).__init__() print 'goes child2' class child3(parent2): def __init__(self): print 'is child3' #parent2.__init__(self) super(child3, self).__init__() print 'goes child3' class grandson(child3,child2,child1): def __init__(self): print 'is grandson' #child1.__init__(self) #child2.__init__(self) #child3.__init__(self) super(grandson, self).__init__() print'goes grandson' if __name__=='__main__': grandson() 此时我们查看结果: is grandson is child3 is child2 is child1 is parent1 goes parent1 goes child1 goes child2 is parent2 goes parent2 goes child3 goes grandson 结果很明显,公共基类parent1只被执行一次。
grandson类的继承体系如下图所示:
object | / \ P1 P2 / \ | C1 C2 C3 所以对于类的继承体系,我们可以看做一个图,而每一个类看做一个节点,那么super()机制的执行顺序是按照图的广度优先搜索算法查找super()的父类。
后续总结:
1. super()是一个类名而非函数,super(class, self)事实上调用了super类的初始化函数,产生了一个super对象;
2 super()机制必须要用新式类,否则会报错;
3 super()或直接父类调用最好只选择一种形式。