An infinite iterator will repeat an infinite number of times with no endpoint and no StopIteration exception raised. Infinite iterators are useful when we have unbounded streams of data to process.

A useful itertool that is an infinite iterator is the count() itertool. This infinite iterator will count from a first value until we provide some type of stop condition. The base syntax of the function looks like this:

count(start,[step])

The first argument of count() is the value where we start counting from. The second argument is an optional step that will return current value + step. The step value can be positive, negative, and an integer or float number. It will always default to 1 if not provided.

To show how it’s used in a scenario, suppose we want to quickly count up and print all even numbers from 0 to 20.

We first import our itertools module and then create a loop (this can be a while loop or a for loop), that will iterate through our count() iterator:

import itertools

for i in itertools.count(start=0, step=2):
  print(i)
  if i >= 20:
    break

Here is what happens in the script:

• We set our start argument to 0 so that we start counting from 0.

• We set our step argument to 2 so that way we increment +2 on each iteration.

• We create a stop condition, which is i >= 20, otherwise this for loop would continue printing forever!

And our output becomes:

0
2
4
6
8
10
12
14
16
18
20

Let’s use the count() itertool to manage our pet store!