code: def _view(self, filepath, format):
          
          methodnames = [
              '_view_%s_%s' % (format, backend.PLATFORM),
              '_view_%s' % backend.PLATFORM,
          ]
          for name in methodnames:
              view_method = getattr(self, name, None)
              if view_method is not None:
                  break
          else:
              raise RuntimeError('%r has no built-in viewer support for %r '
                  'on %r platform' % (self.__class__, format, backend.PLATFORM))
          view_method(filepath)
docs: Start the right viewer based on file format and platform.