Question

Problem Set 5:
In the solutions, why do the functions for SubjectTrigger and SummaryTrigger have __init__ functions defined? Don't they just inherit the ones that they define from their superclass anyway?

Answer 1

To write it out, a superclass WordTrigger is created like so:
class WordTrigger(Trigger):
def __init__(self, word):
self.word = word

but then SubjectTrigger and SummaryTrigger have this defined:
# TODO: SubjectTrigger
class SubjectTrigger(WordTrigger):
def __init__(self, word):
WordTrigger.__init__(self, word)

Isn't that unnecessary? Why is it there?

Answer 2

WordTrigger inherits from Trigger, the __init__() function assigns the variable word into the instance of WordTrigger (the local namespace) being declared.

Answer 3

But shouldn't that __init__() function be inherited anyway? I understand the purpose of __init__, but not why the valid one from the superclass is being overwritten by an identical one in the subclass.

Answer 4

In that case, the __init__() function of the superclass is being overridden by the subclass, just like any other method.