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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _view(self, filepath, format):
 """Start the right viewer based on file format and platform."""

        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)