问题：
在把ckpt 文件转成pb 文件时候，Matplotlib qt-based backends require an external PyQt4,PyQt5 PySide PySide2 to be installed but not found
解决方法：
sudo gedit /root/anaconda3/envs/tensorflow/lib/python3.6/site-packages/object_detection-0.1-py3.6.egg/object_detection/utils/visualization_utils.py

原来是matplotlib.use(‘QT5Agg’)
更改成如上就OK了