Update main.py

main.py

@@ -39,7 +39,8 @@ def document_to_xml(document):
     :return: XML格式字符串
     """
     xml = StringIO()
-    document.save(xml)
+    with open(xml, 'wb') as f:
+    document.save(f)
     xml.seek(0)
     return xml.read()