我想运行以下命令：
import nltk
nltk.download('all')
但是我遇到了这个错误。
Traceback (most recent call last):
File "./update.py", line 3, in <module>
nltk.download('all')
File "/usr/lib/python3.6/site-packages/nltk/downloader.py", line 664, in download
for msg in self.incr_download(info_or_id, download_dir, force):
File "/usr/lib/python3.6/site-packages/nltk/downloader.py", line 534, in incr_download
try: info = self._info_or_id(info_or_id)
File "/usr/lib/python3.6/site-packages/nltk/downloader.py", line 508, in _info_or_id
return self.info(info_or_id)
File "/usr/lib/python3.6/site-packages/nltk/downloader.py", line 875, in info
self._update_index()
File "/usr/lib/python3.6/site-packages/nltk/downloader.py", line 825, in _update_index
ElementTree.parse(compat.urlopen(self._url)).getroot())
File "/usr/lib/python3.6/xml/etree/ElementTree.py", line 1196, in parse
tree.parse(source, parser)
File "/usr/lib/python3.6/xml/etree/ElementTree.py", line 597, in parse
self._root = parser._parse_whole(source)
xml.etree.ElementTree.ParseError: not well-formed (invalid token): line 23, column 143
我是Python的新手，所以不太确定应该做什么。 我查看了上面报告的源模块并注意到它正在尝试下载xml文件。所以我运行了下面的命令，并没有出现任何错误。
compat.urlopen('https://raw.githubusercontent.com/nltk/nltk_data/gh-pages/index.xml')
所以我认为问题不在下载上，而是在解析器上。有人可以建议我从这里怎么继续吗？