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):
2
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”.