update

Author: SusuZzhang

README.md

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 * p18_打开网页   [源码下载](p18_打开网页)    [博文地址](https://xugaoxiang.com/2021/08/05/pyqt5-18-pyqtwebengine/)
 
 * p19_跑马灯   [源码下载](p19_跑马灯)    [博文地址](https://xugaoxiang.com/2021/10/08/pyqt5-19-marquee/)
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 * p20_柱状图 [源码下载](p20_柱状图)    [博文地址](https://xugaoxiang.com/2022/03/16/pyqt5-20-barchart/)