How do I add constraints to Itertools Product?

Question

I am trying to list all products with numbers = [1,2,3,4,5,6,7,8] string length of 4 with some constraints.

Position 0 must be < 8
Positions 2 and 3 must be < 6

With the current code it is printing every possible combination so I was wondering how do I go about filtering it?

import itertools

number = [1,2,3,4,5,6,7,8]

result = itertools.product(number, repeat=4)

for item in result:
    print(item)

I’ve tried using if product[0] < 8 or product[2] < 6 or product[3] < 6: but I don’t know where to fit in or how to format it.

Asked By: CluelessDumbo

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Source

Answer 1

Use and rather than or.

for item in result:
    if item[0] < 8 and item[2] < 6 and item[3] < 6:
        print(item)

Answered By: Barmar

Answer 2

You have to use and instead of or to get Positions 2 and 3 must be < 6 and Position 0 must be < 8. And put this statement in the for loop if item[0] < 8 and item[2] < 6 and item[3] < 6:

so your final code should be:

import itertools

number = [1,2,3,4,5,6,7,8]

result = itertools.product(number, repeat=4)

for item in result:
    if item[0] < 8 and item[2] < 6 and item[3] < 6:
        print(item)

Answered By: Shounak Das

Answer 3

I think you can simplify this and avoid wasting a lot of cycles by looking at the inputs carefully.

repeat=4 means that you want to iterate over the following:

[1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, 3, 4, 5, 6, 7, 8]

However, what your question is asking is how to iterate through

[1, 2, 3, 4, 5, 6, 7]
[1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]

Since the conditions on the inputs are independent (the value of one element is not what restricts the others), you can adjust the inputs instead of filtering elements after the fact.

I suggest you just iterate over the sequences you want directly instead of filtering the output. You don’t need to make actual lists: a range object will be much more efficient:

itertools.product(range(1, 8), range(1, 9), range(1, 6), range(1, 6))

Answered By: Mad Physicist

How do I add constraints to Itertools Product?

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