bs4.FeatureNotFound: Couldn't find a tree builder with the features you requested: lxml. Do you need to install a parser library?

环境是win10 python3.5

安装beautifulsoup后，运行测试报错

from bs4 import BeautifulSoup
soup = BeautifulSoup('<p>Hello</p>', 'lxml')
print(soup.p.string)

Traceback (most recent call last):
  File "C:UsersLenovoDesktopSpider_1.py", line 6, in <module>
    soup = BeautifulSoup(req.content,"lxml")
  File "C:UsersLenovoAppDataLocalProgramsPythonPython35libsite-packagess4\__init__.py", line 165, in __init__
    % ",".join(features))
bs4.FeatureNotFound: Couldn't find a tree builder with the features you requested: lxml. Do you need to install a parser library?

经过测试发现是lxml的问题，使用 pip install lxml时，自动安装的 4.1.1版本，

下载lxml 3.7.3  安装后，问题解决