解决 Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure. 问题

1， 安装 tk-dev 和 python3-tk

sudo apt-get install tk-dev
sudo apt install python3-tk

2，修改 matplotlibrc 文件
sudo geidt  ~/.../lib/python3.6/site-packages/matplotlib/mpl-data/matplotlibrc
搜索：#backend      : Agg
替换为:     backend      : TkAgg

3，如果需要，重新安装 matplotlib：
pip uninstall -y matplotlib
pip --no-cache-dir install -U matplotlib

来源：https://blog.csdn.net/Merlin_Bloom/article/details/100124596