A handful of excellent resources exist for learning what functions are available in the itertools module. The docs themselves are a great place to start.

The thing about itertools, though, is that it is not enough to just know the definitions of the functions it contains. The real power lies in composing these functions to create fast, memory-efficient, and good-looking code.

This article takes a different approach. Rather than introducing itertools to you one function at a time, you will construct practical examples designed to encourage you to “think iteratively.” In general, the examples will start simple and gradually increase in complexity.

# Import combinations with replacements from itertools
from itertools import combinations_with_replacement

Create a list of objects

# Create a list of objects to combine
list_of_objects = ['warplanes', 'armor', 'infantry']

Find all combinations (with replacement) for the list

# Create an empty list object to hold the results of the loop
combinations = []

# Create a loop for every item in the length of list_of_objects, that,
for i in list(range(len(list_of_objects))):
    # Finds every combination (with replacement) for each object in the list
    combinations.append(combinations_with_replacement(list_of_objects, i+1))
[<itertools.combinations_with_replacement at 0x7f85d03c6408>,
 <itertools.combinations_with_replacement at 0x7f85d03c6458>,
 <itertools.combinations_with_replacement at 0x7f85d03c64a8>]
# Flatten the list of iterators into a single list
combinations = [i for row in combinations for i in row]

# View the results
 ('warplanes', 'warplanes'),
 ('warplanes', 'armor'),
 ('warplanes', 'infantry'),
 ('armor', 'armor'),
 ('armor', 'infantry'),
 ('infantry', 'infantry'),
 ('warplanes', 'warplanes', 'warplanes'),
 ('warplanes', 'warplanes', 'armor'),
 ('warplanes', 'warplanes', 'infantry'),
 ('warplanes', 'armor', 'armor'),
 ('warplanes', 'armor', 'infantry'),
 ('warplanes', 'infantry', 'infantry'),
 ('armor', 'armor', 'armor'),
 ('armor', 'armor', 'infantry'),
 ('armor', 'infantry', 'infantry'),
 ('infantry', 'infantry', 'infantry')]