# Python Lessons – 6.8 The itertools module

## The itertools module

The itertools module is a module in the standard Python library that contains many functions that are very useful in functional programming, especially in iterations.

• The count() function starts counting from a certain value.
• The cycle() function performs an infinite iteration on an iterable object
• The repeat() function repeats an object, either infinte times or for a given value of times.

Let’s see an example

``````from itertools import count
for i in count(4):
if i > 10:
break
print(i) ``````

if you run it, you get:

``````>>>
4
5
6
7
8
9
10``````

## Other Functions

There are other functions within the module that work similar to map () and filter ().

• takewhile () – takes the elements of an iterable object as long as a predicate function remains True
• chain () – combines various iterable objects into one iterable object
• accumulate () – returns the total number of values in an iterable object.

Let’s see an example

``````from itertools import accumulate, takewhile, chain
lista1 = list(accumulate(range(7)))
print(lista1)
lista2 = list(takewhile(lambda x: x<5, lista1))
print(lista2)
print(list(chain(lista1,lista2))) ``````

eseguendo

``````>>>
[0, 1, 3, 6, 10, 15, 21]
[0, 1, 3]
[0, 1, 3, 6, 10, 15, 21, 0, 1, 3]``````

## Combinatorial functions

There are combinatorial functions in the itertools module as product() and permutation(). These functions are very useful when you want to get all the possible combinations of the elements.

``````from itertools import permutations, product
chars = ("A","B","C")
products = list(product(chars,chars))
combinations = list(permutations(lettere))
print(products)
print(combinations) ``````

if you run it, you get

``````>>>
[('A', 'A'), ('A', 'B'), ('A', 'C'), ('B', 'A'), ('B', 'B'), ('B', 'C'), ('C', 'A'), ('C', 'B'), ('C', 'C')]
[('A', 'B', 'C'), ('A', 'C', 'B'), ('B', 'A', 'C'), ('B', 'C', 'A'), ('C', 'A', 'B'), ('C', 'B', 'A')]``````

⇐ Go to Python Lesson 6.7 – Sets

Go to Python Lesson 7.1 – Classes⇒

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