lxml.etree.SerialisationError: IO_ENCODER about gitbook2pdf HOT 2 OPEN

reinstall lxml package could resolve this problem，in my case on centos7 , i use lxml4.2
pip3.7 uninstall lxml && pip3.7 install lxml==4.2

from gitbook2pdf.

I have the same problem.

retrying : https://www.math.pku.edu.cn/teachers/lidf/docs/Rbook/html/_Rbook/prog-io.html
Traceback (most recent call last):
File "gitbook.py", line 5, in
Gitbook2PDF(url).run()
File "/home/flood/soft/gitbook2pdf/gitbook2pdf/gitbook2pdf.py", line 198, in run
loop.run_until_complete(self.crawl_main_content(content_urls))
File "/usr/lib/python3.8/asyncio/base_events.py", line 616, in run_until_complete
return future.result()
File "/home/flood/soft/gitbook2pdf/gitbook2pdf/gitbook2pdf.py", line 220, in crawl_main_content
await asyncio.gather(*tasks)
File "/home/flood/soft/gitbook2pdf/gitbook2pdf/gitbook2pdf.py", line 241, in gettext
text = ChapterParser(metatext, title, level, ).parser()
File "/home/flood/soft/gitbook2pdf/gitbook2pdf/gitbook2pdf.py", line 105, in parser
return html.unescape(ET.tostring(context).decode())
File "src/lxml/etree.pyx", line 3437, in lxml.etree.tostring
File "src/lxml/serializer.pxi", line 139, in lxml.etree._tostring
File "src/lxml/serializer.pxi", line 199, in lxml.etree._raiseSerialisationError
lxml.etree.SerialisationError: IO_ENCODER

from gitbook2pdf.