The itertools is a built-in module in Python 3 and is helpful for us to use a more pythonic way to manipulate the iterables (e.g., list, set, tuple, etc.).
Another advantage of itertools is it also returns the generator type instances that have benefits of lazy evaluation from all of its methods.
In this section, we will discuss the third part of itertools. The methods in this section are all about the combinatoric methods in discrete mathematics.
This table takes Python documentation #product as reference.
| Arguments | Results | Example |
|---|---|---|
iterables, repeat=1 |
cartesian products (nested-loop) | product("ABC", repeat=2)= AA, AB, AC, BA, BB, BC, CA, CB, CC |
from itertools import product
gen = product("AB", "CD")
list(gen) # [AC, AD, BC, BD]
gen = product("AB", repeat=2)
list(gen) # [AA, AB, BA, BB]
gen = product("AB", "CD", repeat=2)
list(gen)
# [ACAC, ACAD, ACBC, ACBD,
# ADAC, ADAD, ADBC, ADBD,
# BCAC, BCAD, BCBC, BCBD,
# BDAC, BDAD, BDBC, BDBD]This table takes Python documentation #permutations as reference.
| Arguments | Results | Example |
|---|---|---|
iterable, r=len(iterable) |
permutation with length r |
permutations("ABC", r=2)= AB, AC, BA, BC, CA, CB |
gen = permutations("ABC") # same as r=3
list(gen) # [ABC, ACB, BAC, BCA, CAB, CBA]
gen = permutations("ABC", r=2)
list(gen) # [AB, AC, BA, BC, CA, CB]
gen = permutations("ABC", r=1)
list(gen) # [A, B, C]This table takes Python documentation #combinations as reference.
| Arguments | Results | Example |
|---|---|---|
iterable, r |
combination with length r |
combinations("ABC", 2)= AB, AC, BC |
gen = combinations("ABC", 1)
list(gen)
# [A, B, C]
gen = combinations("ABC", 2)
list(gen)
# [AB, AC, BC]
gen = combinations("ABC", 3)
list(gen)
# [ABC]This table takes Python documentation #combinations_with_replacement as reference.
| Arguments | Results | Example |
|---|---|---|
iterable, r |
combination with length r and repeated elements |
combinations_with_replacement("ABC", 2)= AA, AB, AC, BB, BC, CC |
gen = combinations_with_replacement("ABC", 1)
list(gen)
# [A, B, C]
gen = combinations_with_replacement("ABC", 2)
list(gen)
# [AA, AB, AC,
# BB, BC,
# CC]
gen = combinations_with_replacement("ABC", 3)
list(gen)
# [AAA, AAB, AAC, ABB, ABC, ACC,
# BBB, BBC, BCC,
# CCC]| Article | Link |
|---|---|
| Python documentation - itertools | https://docs.python.org/3/library/itertools.html |
| Python Tutorial: Itertools Module - Iterator Functions for Efficient Looping | https://www.youtube.com/watch?v=Qu3dThVy6KQ |
| Python 好用模組介紹 - itertools & more-itertools | https://myapollo.com.tw/zh-tw/python-itertools-more-itertools/ |
| Python標準庫之itertools庫的使用方法 | https://codertw.com/%E7%A8%8B%E5%BC%8F%E8%AA%9E%E8%A8%80/364249/ |