Question

I have a integer list say l1=[a,b,c] and _1to9=range(1,10). I’d like to get this:

 [a*i1+b*i2+c*i3 for i1 in _1to9 for i2 in _1to9 for i3 in _1to9]

but the problem is that the l1 is not necessarily a list of 3 elements. so how do I generalize?

EDIT: to help visualize what I’m trying to achieve:

 >>> l1=[10001,1010, 100]
 >>> [l1[0]+i1+l1[1]*i2+l1[2]*i3 for i1 in _1to9 for i2 in _1to9 for i3 in _1to9]

Answer 1

Some basic math might help here. First, realise that a*i1+b*i2+c*i3 is the inner (dot) product of two three-element lists, which can be generalized to

def dot_product(a, b):
    return sum(x * y for x, y in zip(a, b))

and for i1 in _1to9 for i2 in _1to9 for i3 in _1to9 loops over the Cartesian product of [_1to9] * 3. That’s in the Python standard library as itertools.product, so you’ve got

[dot_product([a, b, c], x) for x in itertools.product(_1to9, repeat=3)]

Generalizing that to arbitrary lists l gives

[dot_product(l, x) for x in itertools.product(_1to9, repeat=len(l))]