How to iterate in a cartesian product of lists

Question

I would like to iterate in a for loop using 3 (or any number of) lists with any number of elements, for example:

from itertools import izip
for x in izip(["AAA", "BBB", "CCC"], ["M", "Q", "S", "K", "B"], ["00:00", "01:00", "02:00", "03:00"]):
    print x

but it gives me:

('AAA', 'M', '00:00')
('BBB', 'Q', '01:00')
('CCC', 'S', '02:00')

I want:

('AAA', 'M', '00:00')
('AAA', 'M', '01:00')
('AAA', 'M', '02:00')
.
.

('CCC', 'B', '03:00')

Actually I want this:

for word, letter, hours in [cartesian product of 3 lists above]
    if myfunction(word,letter,hours):
       var_word_letter_hours += 1

Solution 1

You want to use the product of the lists:

from itertools import product

for word, letter, hours in product(["AAA", "BBB", "CCC"], ["M", "Q", "S", "K", "B"], ["00:00", "01:00", "02:00", "03:00"]):

Demo:

>>> from itertools import product
>>> for word, letter, hours in product(["AAA", "BBB", "CCC"], ["M", "Q", "S", "K", "B"], ["00:00", "01:00", "02:00", "03:00"]):
...     print word, letter, hours
... 
AAA M 00:00
AAA M 01:00
AAA M 02:00
AAA M 03:00
...
CCC B 00:00
CCC B 01:00
CCC B 02:00
CCC B 03:00

Solution 2

Use itertools.product:

import itertools

for x in itertools.product(["AAA", "BBB", "CCC"],
                           ["M", "Q", "S", "K", "B"],
                           ["00:00", "01:00", "02:00", "03:00"]):
    print x

output:

('AAA', 'M', '00:00')
('AAA', 'M', '01:00')
...
('CCC', 'B', '02:00')
('CCC', 'B', '03:00')

Comments

[user4815162342]

This solution makes more sense if you need additional processing at different loop levels. However, the OP just wants to iterate over the triples, which with this approach must be constructed manually. Nested for loops is that they add as much indentation as there are lists, which can be a real issue for readability.

[FinanceGuyThatCantCode]

This is also no good if the number of nested loops is not known at compile time (or whatever you want to call compile time in python)

[Arthur Tacca]

@FinanceGuyThatCantCode I already explicitly mentioned that in my answer, where I said it would be no good "if you have an arbitrary list of lists that you want to take the Cartesian product of"