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:


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!



We have several 13.5lb bags of dog food to display. Our single shelving unit however can only hold a maximum of 1,000lbs. Let’s figure out how many bags of food we can display!

First, import the itertools module at the top line of the code editor.


Next, initialize a for loop with a count() iterator that keeps track of the weight on the shelf.

Within the for loop body:

  • Provide a stop condition using max_capacity to terminate the loop
  • Increment num_bags on each iteration.

Print the num_bags result to see how many bags will fit on the shelving unit.

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