'write a chart'

def write(self):

    root = Element('c:chartSpace', {'xmlns:c': 'http://schemas.openxmlformats.org/drawingml/2006/chart', 'xmlns:a': 'http://schemas.openxmlformats.org/drawingml/2006/main', 'xmlns:r': 'http://schemas.openxmlformats.org/officeDocument/2006/relationships'})
    SubElement(root, 'c:lang', {'val': self.chart.lang})
    self._write_chart(root)
    self._write_print_settings(root)
    self._write_shapes(root)
    return get_document_content(root)
