python父类能够访问子类属性，即使没在父类中定义的属性

如题。

In [25]: class A(object):
    ...:     def f(self):
    ...:          print(self.p)
    ...:         

In [26]: class B(A):
    ...:     p = 'This is in B'
    ...:     

In [27]: B().f()
This is in B