python 3.7安裝lxml

python bs4解析網頁時，報錯： bs4.FeatureNotFound: Couldn't find a tree builder with the features you requested: lxml. Do you need to install a parser library? 原因是沒有安裝lxml 用 pip install lxml,提示安裝失敗 用以下的方式，安裝成功了

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