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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 export_osm_file(self):
 """Generate OpenStreetMap element tree from ``Osm``."""

        osm = create_elem('osm', {'generator': self.generator,
                                  'version': self.version})
        osm.extend(obj.toosm() for obj in self)

        return etree.ElementTree(osm)