Overriding an inherited property setter

Question

I have a class called Node that has an importance setter and getter, below:

class Node:

    @property
    def importance(self):
        return self._importance

    @importance.setter
    def importance(self, new_importance):
        if new_importance is not None:
            new_importance = check_type_and_clean(new_importance, int)
            assert new_importance >= 1 and new_importance <= 10
        self._importance = new_importance

Later on, I have a class Theorem that inherits from Node. The only difference between a Theorem and a Node, as far as importance is concerned, is that a Theorem must have an importance of at least 3.

How can a Theorem inherit the importance setter, but add on the additional constraint that importance >= 3?

I tried to do it this way:

class Theorem(Node):

    @importance.setter
    def importance(self, new_importance):
        self.importance = new_importance # hoping this would use the super() setter
        assert self.importance >= 3

Answer 1

You can refer to the existing property directly through the Node class, and use the property's setter method to create a new property from it:

class Theorem(Node):
    @Node.importance.setter
    def importance(self, new_importance):
        # You can change the order of these two lines:
        assert new_importance >= 3
        Node.importance.fset(self, new_importance)

This will create a new property into Theorem class that uses the getter method from Node.importance but replaces the setter method with a different one. That's how properties in general work: calling a property's setter returns a new property with a custom setter, which usually just replaces the old property.

You can learn more about how properties work by reading this answer (and the question too).