子类调用父类,必须调用父类的__init__方法

python 中进行面向对象编程,当在资历的实例调用父类的属性时,

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

# !/usr/bin/env python
# -*- coding: utf-8 -*-
class A(object):
    def __init__(self):
        self.a = 5

    def function_a(self):
        print('I am from A, my value is %d' % self.a)


class B(A):
    def __init__(self):
        self.b = 10

    def function_b(self):
        print('I am from B, my value is %d' % self.b)
        self.function_a()    # 调用类A的方法，出错


if __name__ == '__main__':
    b = B()
    b.function_b()


C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/wxpython/t6.py
I am from B, my value is 10
Traceback (most recent call last):
  File "C:/Users/TLCB/PycharmProjects/untitled/wxpython/t6.py", line 22, in <module>
    b.function_b()
  File "C:/Users/TLCB/PycharmProjects/untitled/wxpython/t6.py", line 17, in function_b
    self.function_a()    # 调用类A的方法，出错
  File "C:/Users/TLCB/PycharmProjects/untitled/wxpython/t6.py", line 8, in function_a
    print('I am from A, my value is %d' % self.a)
AttributeError: 'B' object has no attribute 'a'

Process finished with exit code 1