def METHOD_NAME(self):
    """
    Launch external viewer for the graphics file.
    .. note::
        Does not actually launch a new process when doctesting.
    EXAMPLES::
        sage: from sage.structure.graphics_file import GraphicsFile
        sage: g = GraphicsFile('/tmp/test.png', 'image/png')
        sage: g.launch_viewer()
    """
    if sage.doctest.DOCTEST_MODE:
        return
    if self.mime() == Mime.JMOL:
        return self._launch_jmol()
    from sage.misc.viewer import viewer
    command = viewer(preferred_filename_ext[self.mime()])
    os.system('{0} {1} 2>/dev/null 1>/dev/null &'
              .format(command, self.filename()))
    # TODO: keep track of opened processes...