1. I don't know why
py -3 -m pip install matplotlib
This installation will report an error/missing freetype and png components/finally did not solve the problem/
Solution:
https://www.lfd.uci.edu/~gohlke/pythonlibs/#pyside
Find Matplotlib , a 2D plotting library.
安装matplotlib的必备组件：Requires numpy, dateutil, pytz, pyparsing, kiwisolver, cycler, setuptools, and optionally pillow, pycairo, tornado, wxpython, pyside, pyqt4, ghostscript, miktex, ffmpeg, mencoder, avconv, or imagemagick.
Then download the relevant whl file and install it with pip!