code: def find_difference(s, t):
      ret = 0
      for ch in s + t:
          # ord(ch) return an integer representing the Unicode code point of that character
          ret = ret ^ ord(ch)
      # chr(i) Return the string representing a character whose Unicode code point is the integer i
      return chr(ret)
  
label_desc: Use image node_id 1 for calling a global function with example usage: find_difference(s, t) and returns: chr