code: def censor_non_alphanum(s):
      
  
      def censor(ch):
          if (ch >= 'A' and ch <= 'z') or (ch >= '0' and ch <= '9'):
              return ch
          return '*'
  
      return ''.join([censor(ch) for ch in s])
docs: Returns s with all non-alphanumeric characters replaced with *