code: def _strtobool(val):
      
      val = val.lower()
      if val in ('y', 'yes', 't', 'true', 'on', '1'):
          return 1
      elif val in ('n', 'no', 'f', 'false', 'off', '0', ''):
          return 0
      else:
          raise ValueError('Invalid truth value: {0}'.format(val))
docs: Convert a string representation of truth to true (1) or false (0).
  
      True values are 'y', 'yes', 't', 'true', 'on', and '1'; false values
      are 'n', 'no', 'f', 'false', 'off', '0' and ''.  Raises ValueError if
      'val' is anything else.