input: Write a python function to generate all permutations of a string up to a given length.
  assert permutateString("AB", 2) == [['A', 'B'], ['B', 'A']]
  assert permutateString("ABC", 2) == [['A', 'B'], ['A', 'C'], ['B', 'A'], ['B', 'C'], ['C', 'A'], ['C', 'B']]
  assert permutateString("ABCD", 2) == [['A', 'B'], ['A', 'C'], ['A', 'D'], ['B', 'A'], ['B', 'C'], ['B', 'D'], ['C', 'A'], ['C', 'B'], ['C', 'D'], ['D', 'A'], ['D', 'B'], ['D', 'C']]
output: from itertools import permutations
  
  def permutateString(s, length):
      return [list(p) for p in permutations(s, length)]