Question

How do I do the following in Python:

array_1 = [x1, x2, x3, x4, x5, x6, ....]
array_2 = [y1, y2, y3]

array_3 = [(x1-y1), (x2-y2), (x3-y3), (x4-y1), (x5-y2), (x6-y3)]

The number of elements in array_2 is always less than the number of elements in array_1.

array_1 and array_2 have an arbitrary number of elements.

[num of elements in array_1] mod [number of elements in array_2] = 0

Answer 1

Itertools has loads of tools to accommodate your problem

Understanding your problem

1. One of the array is shorter than the other
2. The Shorter array should be cycled until the longer array is exhausted
3. Create a pair of the longer array and the cycled shorter array
4. Subtract the elements within the pair

So here is the implementation

>>> arr1 = range(1,10)
>>> arr2 = range(20,23)
>>> from operator import sub
>>> from itertools import izip, cycle, starmap
>>> list(starmap(sub, izip(arr1, cycle(arr2))))
[-19, -19, -19, -16, -16, -16, -13, -13, -13]