Python – Itertools.cycle()

Iterator is defined as object types which contains values that can be accessed or iterated using a loop. There are different iterators that come built-in with Python such as lists, sets, etc. Itertools is the Python module that contains some inbuilt functions for generating sequences using iterators. This module 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. There are different types of Iterators

1. Infinite Iterators: These type of iterators produce infinite sequences.
2. Short sequence iterators: These iterators produces the sequences which terminate after certain iterations.
3. Combinatorics generator functions: These generators produce the sequences in combinations related to the input arguments.

Itertools.cycle()

• The Function takes only one argument as input it can be like list, String, tuple, etc
• The Function returns the iterator object type
• In the implementation of the function the return type is yield which suspends the function execution without destroying the local variables. It is used by the generators which produce intermediate results
• It iterates through each element in the input argument and yields it and repeats the cycle and produces an infinite sequence of the argument

The below-mentioned Python program illustrates the functioning of the cycle function. It takes string type as an argument and produces the infinite sequence. 

Python3

import itertools


# String for sequence generation
Inputstring ="Geeks"

# Calling the function Cycle from
# itertools and passing string as
#an argument and the function returns
# the iterator object
StringBuffer = itertools.cycle(Inputstring)
SequenceRepeation = 0
SequenceStart = 0
SequenceEnd = len(Inputstring)

for output in StringBuffer:
    if(SequenceStart == 0):
        print("Sequence % d"%(SequenceRepeation + 1))

    # Cycle function iterates through each
    # element and produces the sequence
    # and repeats it the sequence
    print(output, end =" ")

    # Checks the End of the Sequence according
    # to the given input argument
    if(SequenceStart == SequenceEnd-1):

        if(SequenceRepeation>= 2):
            break
        else:
            SequenceRepeation+= 1
            SequenceStart = 0
            print("\n")
    else:
        SequenceStart+= 1

Output:

Sequence  1
G e e k s 

Sequence  2
G e e k s 

Sequence  3
G e e k s

The itertools.cycle function also works with the Python Lists. The below-mentioned Python program illustrates the functioning. It takes the Python list as an argument and produces the infinite sequence. 

Python3

import itertools


# List for sequence generation
Inputlist = [1, 2, 3]

# Calling the function Cycle from
# itertools and passing list as
# an argument and the function
# returns the iterator object
ListBuffer = itertools.cycle(Inputlist)
SequenceRepeation = 0
SequenceStart = 0
SequenceEnd = len(Inputlist)

for output in ListBuffer:
    if(SequenceStart == 0):
        print("Sequence % d"%(SequenceRepeation + 1))

    # Cycle function iterates through
    # each element and produces the
    # sequence and repeats it the sequence
    print(output, end =" ")

    # Checks the End of the Sequence according
    # to the given input argument
    if(SequenceStart == SequenceEnd-1):

        if(SequenceRepeation>= 2):
            break
        else:
            SequenceRepeation+= 1
            SequenceStart = 0
            print("\n")
    else:
        SequenceStart+= 1

Output:

Sequence  1
1 2 3 

Sequence  2
1 2 3 

Sequence  3
1 2 3