在python中将字符串写入xml

Question

所以我还在学习如何使用xml.etree.ElementTree来创建xml文档。我想把字符串的句子写成xml文件。

这是我的代码：

   import sys
   import os
   import re
   import xml.etree.ElementTree as ET

   input_f = "test.txt"
   output_f = "results.txt"
   lines = open(input_f, "r").readlines()
   sentences = [x.strip() for x in ' '.join(lines).replace("\n","").split(".")]

    with open(output_f,"w") as f:
        for sentence in sentences:
            if sentence != "":
               f.write("%s\n\n" % sentence)

    xml_list = []

    #convert sentences to xml    
    for line in output_f:
        event_descri = ET.fromstring(line, parser=None)
        xml_list.append(event_descri)

    # writes to xml file
    with open("chronology.xml", "w") as f:
      f.write(ET.tostring(xml_list))

这是我的错误：

    File "C:\Python34\lib\xml\etree\ElementTree.py", line 1326, in XML
    return parser.close()
    File "<string>", line None
    xml.etree.ElementTree.ParseError: syntax error: line 1, column 0

这里发生了什么？有人可以帮忙吗？