前言python中进行面向对象编程，当在子类的实例中调用父类的属性时，由于子类的__init__方法重写了父类的__init__方法，如果在子类中这些属性未经过初始化，使用时就会出错。例如以下的代码:class A(object):
def __init__(self):
self.a = 5
def function_a(self):
print('I am from A, my value i
先贴一个OC中类的继承关系图 The UIResponder class defines an interface for objects that respond to and handle events. It is the superclass of UIApplication, UIViewand its subclasses (which incl
