code: def friendly_number(num):
      
      # Convert to a (shorter) string for human consumption
      string = ""
      # The length of the string can be determined by STRING_LENGTH or by how many
      # characters are necessary to present a base 30 representation of SIZE.
      while STRING_LENGTH and len(string) <= STRING_LENGTH \
              or len(VALID_CHARS) ** len(string) <= SIZE:
          # PREpend string (to remove all obvious signs of order)
          string = VALID_CHARS[num % len(VALID_CHARS)] + string
          num = num / len(VALID_CHARS)
      return string
docs: Convert a base 10 number to a base X string.
          Charcters from VALID_CHARS are chosen, to convert the number
          to eg base 24, if there are 24 characters to choose from.
          Use valid chars to choose characters that are friendly, avoiding
          ones that could be confused in print or over the phone.