Make class iterable Python

Python has two main constructs iterator and iterables Iteration protocol. The Iterable object implements __iter__() method and returns an Iterator object. The Iterator object implements the __next__() method and raises a StopIteration when the elements of the iterable object are exhausted.

The Iterator object is itself an Iterable as it must also implement the __iter__() method and simply return itself.

To make your class Iterable we need to override __iter__() function inside our class i.e.

def __iter__(self):
    pass

To create an Iterator class we need to override the next() function inside our class i.e.

def __next__(self):
    pass

Make class iterable Python example

Simple example code implements and uses Iterables and Iterators.

class Counter:
    def __init__(self, low, high):
        self.current = low - 1
        self.high = high

    def __iter__(self):
        return self

    def __next__(self): # Python 2: def next(self)
        self.current += 1
        if self.current < self.high:
            return self.current
        raise StopIteration


for c in Counter(1, 5):
    print(c)

Output:

• The __iter__ returns the iterator object and is implicitly called at the start of loops.
• The __next__() method returns the next value and is implicitly called at each loop increment. This method raises a StopIteration exception when there is no more value to return, which is implicitly captured by looping constructs to stop iterating.

Why should we make a Custom class Iterable?

Answer: Custom classes created by us are by default, not Iterable. If we want to iterate over the objects of our custom class then we need to make them Iterable and also create an Iterator class for them.

Do comment if you have any doubts or suggestions on this Python iterable topic.

Note: IDE: PyCharm 2021.3.3 (Community Edition)

Windows 10

Python 3.10.1

All Python Examples are in Python 3, so Maybe its different from python 2 or upgraded versions.