Python 3.x 您需要安装解析器库吗？当它已经存在的时候

我在尝试使用beatufulsoup解析html时遇到此错误。我

pip3已经安装了lxml

。包就在那里-

/usr/local/lib/python3.6/site-packages/lxml/

，但我仍然收到这个错误。有人能告诉我出了什么问题吗

FeatureNotFound:找不到具有您所需功能的树生成器 请求：xml。您需要安装解析器库吗

获取文本（url）中的

26 def get_文本（url）：
27 r=urllib.request.urlopen（url.read（））
--->28汤=美汤（r，“lxml”）
29
/usr/local/lib/python3.6/site packages/bs4/uuuuu init_uuu.py in_uuuuinit_uuuuu（self、markup、features、builder、parse_only、from_encoding、exclude_uencoding、**kwargs）
163“找不到具有所需功能的树生成器”
164“请求：%s。是否需要安装解析器库？”
-->165%“，”。连接（功能））
166 builder=builder\u class（）
167如果不是（原始功能==builder.NAME或
FeatureNotFound:找不到具有您请求的功能的树生成器：lxml。是否需要安装解析器库？

<ipython-input-22-0493a00ae0a0> in get_text(url)
     26 def get_text(url):
     27     r = urllib.request.urlopen(url).read()
---> 28     soup = BeautifulSoup(r, "lxml")
     29 

/usr/local/lib/python3.6/site-packages/bs4/__init__.py in __init__(self, markup, features, builder, parse_only, from_encoding, exclude_encodings, **kwargs)
    163                     "Couldn't find a tree builder with the features you "
    164                     "requested: %s. Do you need to install a parser library?"
--> 165                     % ",".join(features))
    166             builder = builder_class()
    167             if not (original_features == builder.NAME or

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