Python Itertools permutations with strings

Question

i want to use itertools permutations for strings instead of just letters.

import itertools
lst = list(permutations(("red","blue"),3))
#This returns []

I know i can do something like:

a = list(permutations(range(3),3))
for i in range(len(a)):
a[i] = list(map(lambda x: 'red' if x==0 else 'blue' if x==1 else 'green',a[i]))

EDIT: I want to key in this as my input, and get this as my output

input: ("red","red","blue")

output:
[(’red’, ’red’, ’red’), (’red’, ’red’, ’blue’),\
(’red’, ’blue’, ’red’), (’red’, ’blue’, ’blue’), (’blue’, ’red’, ’red’), \
(’blue’, ’red’, ’blue’), (’blue’, ’blue’, ’red’), (’blue’, ’blue’, ’blue’)]

what is your expected output? your original idea looks ok to me, the reason why it's returning [] is because you're asking for length-3 permutations in a list of length-2 -- there aren't any! — maxymoo
– maxymoo, Commented Jun 9, 2017 at 4:30
It works perfectly fine to permute strings. However, you cannot take three elements from a list of two, in any order. That is why you get the empty list as output. — JohanL
– JohanL, Commented Jun 9, 2017 at 4:31

Tiny.D · Accepted Answer · 2017-06-10 00:52:17Z

3

You can try with itertools.product like this:

import itertools
lst = list(set(itertools.product(("red","red","blue"),repeat=3))) # use set to drop duplicates
lst

lst will be:

[('red', 'blue', 'red'),
 ('blue', 'red', 'red'),
 ('blue', 'blue', 'red'),
 ('blue', 'blue', 'blue'),
 ('blue', 'red', 'blue'),
 ('red', 'blue', 'blue'),
 ('red', 'red', 'blue'),
 ('red', 'red', 'red')]

Update:

import itertools
lst = list(itertools.product(("red","blue"),repeat=3))
lst

output:

[('red', 'red', 'red'),
 ('red', 'red', 'blue'),
 ('red', 'blue', 'red'),
 ('red', 'blue', 'blue'),
 ('blue', 'red', 'red'),
 ('blue', 'red', 'blue'),
 ('blue', 'blue', 'red'),
 ('blue', 'blue', 'blue')]

edited Jun 10, 2017 at 0:52

answered Jun 9, 2017 at 5:25

Tiny.D

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Silver Over a year ago

How do i get the same output if my input is just ['red' , 'blue'] and i want the same product?

Chiheb Nexus · Accepted Answer · 2017-06-09 05:28:21Z

2

You can do it, also, with combinations from itertools module, like this example:

from itertools import combinations 
final = list(set(combinations(("red","red","blue")*3, 3)))

print(final)

Output:

[('red', 'blue', 'red'),
 ('blue', 'red', 'red'),
 ('blue', 'blue', 'red'),
 ('blue', 'blue', 'blue'),
 ('blue', 'red', 'blue'),
 ('red', 'blue', 'blue'),
 ('red', 'red', 'blue'),
 ('red', 'red', 'red')]

answered Jun 9, 2017 at 5:28

Chiheb Nexus

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