Itertools: Infinite Iterators

Python’s Itertool is a module that provides various functions that work on iterators to produce complex iterators. This module works as a fast, memory-efficient tool that is used either by themselves or in combination to form iterator algebra.

Different types of iterators provided by this module are Infinite Iterators, Combinatoric iterators and Terminating iterators.

Infinite Iterators

Iterator in Python is any Python type that can be used with a ‘for in loop’. Python lists, tuples, dictionaries, and sets are all examples of inbuilt iterators. But it is not necessary that an iterator object has to exhaust, sometimes it can be infinite. Such type of iterators are known as Infinite iterators.

Python provides three types of infinite itertors:

count(start, step): This iterator starts printing from the “start” number and prints infinitely. If steps are mentioned, the numbers are skipped else step is 1 by default.
See the below example for its use with for in loop.

import itertools  
# for in loop  
for i in itertools.count(5, 5):  
    if i == 35:  
        break
    else:  
        print(i, end =" ")
# prints 5 10 15 20 25 30

cycle(iterable): This iterator prints all values in order from the passed container. It restarts printing from the beginning again when all elements are printed in a cyclic manner.

import itertools  
    
count = 0
    
# for in loop  
for i in itertools.cycle('AB'):  
    if count > 7:  
        break
    else:  
        print(i, end = " ")  
        count += 1
# prints A B A B A B A B 

repeat(val, num): This iterator repeatedly prints the passed value infinite number of times. If the optional keyword num is mentioned, then it repeatedly prints num number of times.

import itertools   
      
# using repeat() to repeatedly print number   
print ("Printing the numbers repeatedly : ")   
print (list(itertools.repeat(25, 4)))
# prints
Printing the numbers repeatedly : 
[25, 25, 25, 25]

Try the following excercise in the editor below.

Perform the operations as described in the comments in the order given.