20.3. Call a Parent Method

If you compare the code in the __init__ methods of Point and LabeledPoint, you can see that there is some duplication–the initialization of x and y. We can eliminate the duplication by having LabeledPoint’s __init__() method call (execute) Point’s __init__() method. That way, each class will be responsible for initializing its own instance variables.

All objects keep a reference to the class that created them and every class has a reference to its parent class. You can get an object that represents the parent class using super() and then call a method on that object.

1 class LabeledPoint(Point):
3     def __init__(self, initX, initY, label):
4         super().__init__(initX, initY)
5         self.label = label

In this example, line 4 invokes the __init__() method in Point, passing the values of initX and initY to be used in initializing the x and y instance variables.

Here is a complete code listing showing both classes, with a version of __str__() for LabeledPoint that invokes its parent’s implementation using super() to avoid duplicating the functionality provided in Point.

Finish the code for the Student class below. In the __init__ method for Student call the __init__ method for Person and pass in a first and last name. Then also set the id. In the __str__ method for Student return the id in the form (id: actual_id,) followed by the string returned from the __str__ method in Person. For example, if s = Student("Abby", "Lane", 1) then print(s) should print “id: 1, name: Abby Lane”.

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