Question

Iterators provide a systematic way to access all of the elements in a collection. To define an iterator, we need to add the __iter__() method to the class over which we want to iterate.

Consider the following lines of code:

  odd_numbers = Odds(9)
  for num in odd_numbers:
      print(num)

This code iterates over all the odd numbers less than or equal to 9 starting from the number 1. It assumes that the Odds class is iterable, i.e., it contains an __iter__() method which returns an Iterator object. In this exercise, the Iterator object is an instance of the OddsIterator class and the OddsIterator class must contain the definition of the two methods:

__init__()
__next__()

The __next__() method will be called repeatedly when a collection is being iterated over, and each time it is called, it returns the next value in the collection.

Define two classes: the Odds class and the OddsIterator class so that the for loop above works correctly. The skeleton of the two classes is shown below:

class Odds:
    def __init__( ... ):
        #Stores the number to be reached
    def __iter__(self):
        #Returns an instance of the OddsIterator class

class OddsIterator:
    def __init__(self, upper):
        #Stores the information needed to do the iteration
    def __next__(self):
        #Returns the next number in the iteration
        #raises a StopIteration when there are no more elements

For example:

Test	Result
o = Odds(9) for i in o: print(i)	1 3 5 7 9
o = Odds(1) for i in o: print(i)	1

Answer 1

class Odds:
    def __init__(self, max_value):
        self.max_value = max_value

    def __iter__(self):
        return OddsIterator(self)


class OddsIterator:
    def __init__(self, upper):
        self.current = 1
        self.upper = upper.max_value

    def __next__(self):
        if self.current <= self.upper:
            result = self.current
            self.current += 2
            return result
        else:
            raise StopIteration