permutations.py

def perms(arr):
  if len(arr) == 1:
    return [arr]
  ret = []
  head = arr[:1]
  for tail in perms(arr[1:]):
    for i in range(len(arr)):
      ret.append(tail[i:] + head + tail[:i])
  return ret
  
  print perms([1,2,3,4])