code: def trigger_if_changed(self, obj, old):
          ''' Send a change event notification if the property is set to a
          value is not equal to ``old``.
  
          Args:
              obj (HasProps)
                  The object the property is being set on.
  
              old (obj) :
                  The previous value of the property to compare
  
          Returns:
              None
  
          '''
          new_value = self.__get__(obj, obj.__class__)
          if not self.property.matches(old, new_value):
              self._trigger(obj, old, new_valuef trigger_if_changed(self, obj, old):
          ''' Send a change event notification if the property is set to a
          value is not equal to ``old``.
  
          Args:
              obj (HasProps)
                  The object the property is being set on.
  
              old (obj) :
                  The previous value of the property to compare
  
          Returns:
              None
  
          '''
          new_value = self.__get__(obj, obj.__class__)
          if not self.property.matches(old, new_value):
              self._trigger(obj, old, new_value)
docs: Send a change event notification if the property is set to a
          value is not equal to ``old``.
  
          Args:
              obj (HasProps)
                  The object the property is being set on.
  
              old (obj) :
                  The previous value of the property to compare
  
          Returns:
              None