Detecting class attribute value change and then changing another class attribute

问题

Let's say I have a class called Number

class Number():
  def __init__(self,n):
    self.n=n
    self.changed=None
a = Number(8)
print(a.n) #prints 8
a.n=9
print(a.n) #prints 9

When the n class attribute changes, I want the changed class attribute to be changed to True.

回答1:

Possible with proper use of @propety

class Number():
  def __init__(self,n):
    self._n=n
    self._changed=None

  @property
  def n(self):
      return self._n

  @property
  def changed(self):
      return self._changed

  @n.setter
  def n(self, val):
      # while setting the value of n, change the 'changed' value as well
      self._n = val
      self._changed = True

a = Number(8)
print(a.n) #prints 8
a.n=9
print(a.n) #prints 9
print(a.changed)

Returns:

8
9
True

来源：https://stackoverflow.com/questions/62705053/detecting-class-attribute-value-change-and-then-changing-another-class-attribute