input: Write a Python function to identify the maximum positive integer in a given list.
  assert largest_pos([1,2,3,4,-1]) == 4
  assert largest_pos([0,1,2,-5,-1,6]) == 6
  assert largest_pos([0,0,1,0]) == 1
output: def largest_pos(lst):
      max_pos = -1
      for num in lst:
          if num > max_pos and num > 0:
              max_pos = num
      return max_pos