all possible combinations and subsets of a given array

combs.py

def cross(h, xs):
  return [[h]+x for x in xs]

def combs(xs, n):
  if n == 1:
    return [[x] for x in xs]

  res = []

  head = xs[:-n + 1]
  for i,h in enumerate(head):
    rest = xs[i+1:]
    t = combs(rest,n-1)
    c = cross(h, t)
    res += c

  return res

def subsets(xs, n):
  res = []
  for i in range(1, n + 1):
    res += combs(xs, i)
  return res

print(combs([1,2,3,4,5], 3))

# gives [[1, 2, 3], [1, 2, 4], [1, 2, 5], [1, 3, 4], [1, 3, 5], [1, 4, 5], [2, 3, 4], [2, 3, 5], [2, 4, 5], [3, 4, 5]]


print(subsets([1,2,3], 3))

# gives [[1], [2], [3], [1, 2], [1, 3], [2, 3], [1, 2, 3]]