Turn a list into a tuple of arguments

Question

Python itertools.product() takes coma separated 1D lists and returns a product. I have a list of divisors of a number in a form

l=[[1, a1**1,a1**2,..a1**b1],[1,a2**1,..a2**b2],..[1, an**1, an**2,..an**bn]]

When I pass it to itertools.product() as an argument I don't get the desired result. How can I feed this list of lists of integers to product()?

import itertools

print([list(x) for x in itertools.product([1,2,4],[1,3])]) 
#  [[1, 1], [1, 3], [2, 1], [2, 3], [4, 1], [4, 3]]  #desired

l1=[1,2,4],[1,3] #doesn't work
print([list(x) for x in itertools.product(l1)])
#[[[1, 2, 4]], [[1, 3]]]

l2=[[1,2,4],[1,3]] #doesn't work
print([list(x) for x in itertools.product(l2)])
#[[[1, 2, 4]], [[1, 3]]]

Please share the desired output of your input i.e. `l2=[[1,2,4],[1,3]` — Moinuddin Quadri, Sep 20 '16 at 23:54
Also, you want cartesian product of two lists? Because that is what `itertools.product()` does — Moinuddin Quadri, Sep 20 '16 at 23:55
I want to have a list of all divisors of `n` given the prime factors of n. — sixtytrees, Sep 21 '16 at 00:02

score 3 · Accepted Answer · edited May 23 '17 at 12:32

3

You need to use *l2 within the product() as * unwraps the list. In this case, the value of *[[1,2,4],[1,3]] will be [1,2,4],[1,3]. Here's your code:

l2 = [[1,2,4],[1,3]] 
print([list(x) for x in itertools.product(*l2)])
# Output: [[1, 1], [1, 3], [2, 1], [2, 3], [4, 1], [4, 3]]

Please check: What does asterisk mean in python. Also read regarding *args and **kwargs, you might find it useful. Check: *args and **kwargs in python explained

edited May 23 '17 at 12:32

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answered Sep 20 '16 at 23:57

Moinuddin Quadri

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What is this `*`? I want to read more about it. Worked like charm. – sixtytrees Sep 20 '16 at 23:59
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Check this: https://pythontips.com/2013/08/04/args-and-kwargs-in-python-explained/ Also adding with the answer for others looking for it – Moinuddin Quadri Sep 21 '16 at 00:00
To be precise, you need to know: http://stackoverflow.com/questions/400739/what-does-asterisk-mean-in-python – Moinuddin Quadri Sep 21 '16 at 00:07
My appreciation and best wishes to your rep – sixtytrees Sep 21 '16 at 00:08
@sixtytrees : Thank You :) – Moinuddin Quadri Sep 21 '16 at 00:11

Turn a list into a tuple of arguments

1 Answers1