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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_gpx_file(self):
 """Generate GPX element tree from ``Trackpoints``. Returns: etree.ElementTree: GPX element tree depicting ``Trackpoints`` objects """

        gpx = create_elem('gpx', GPX_ELEM_ATTRIB)
        if not self.metadata.bounds:
            self.metadata.bounds = [j for i in self for j in i]
        gpx.append(self.metadata.togpx())
        track = create_elem('trk')
        gpx.append(track)
        for segment in self:
            chunk = create_elem('trkseg')
            track.append(chunk)
            for place in segment:
                chunk.append(place.togpx())

        return etree.ElementTree(gpx)