code: def ascii_printable(self, keysym):
          
          if 0 <= keysym < 9:
              return False
          elif 13 < keysym < 32:
              return False
          elif keysym > 126:
              return False
          else:
              return True
docs: If the keysym corresponds to a non-printable ascii character this will
          return False. If it is printable, then True will be returned.
  
          ascii 11 (vertical tab) and ascii 12 are printable, chr(11) and chr(12)
          will return '\x0b' and '\x0c' respectively.