code: def _get_exclusive_error_codes(cls, options):
          
          codes = set(ErrorRegistry.get_error_codes())
          checked_codes = None
  
          if options.ignore is not None:
              ignored = cls._expand_error_codes(options.ignore)
              checked_codes = codes - ignored
          elif options.select is not None:
              checked_codes = cls._expand_error_codes(options.select)
          elif options.convention is not None:
              checked_codes = getattr(conventions, options.convention)
  
          # To not override the conventions nor the options - copy them.
          return copy.deepcopy(checked_codes)
docs: Extract the error codes from the selected exclusive option.