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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 _write_xml(xmlfile, srcs):
 """Save the ROI model as an XML """

        root = ElementTree.Element('source_library')
        root.set('title', 'source_library')

        for src in srcs:
            src.write_xml(root)

        output_file = open(xmlfile, 'w')
        output_file.write(utils.prettify_xml(root))