[max@torus ~]$ python
Python 3.6.6 (default, Jun 27 2018, 13:11:40) 
[GCC 8.1.1 20180531] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import matplotlib.pyplot
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/qt_compat.py", line 201, in <module>
    from PySide import QtCore, QtGui, __version__, __version_info__
ModuleNotFoundError: No module named 'PySide'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.6/site-packages/matplotlib/pyplot.py", line 115, in <module>
    _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/__init__.py", line 62, in pylab_setup
    [backend_name], 0)
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_qt5agg.py", line 15, in <module>
    from .backend_qt5 import (
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_qt5.py", line 19, in <module>
    import matplotlib.backends.qt_editor.figureoptions as figureoptions
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/qt_editor/figureoptions.py", line 20, in <module>
    import matplotlib.backends.qt_editor.formlayout as formlayout
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/qt_editor/formlayout.py", line 54, in <module>
    from matplotlib.backends.qt_compat import QtGui, QtWidgets, QtCore
  File "/usr/lib/python3.6/site-packages/matplotlib/backends/qt_compat.py", line 204, in <module>
    "Matplotlib qt-based backends require an external PyQt4, PyQt5,\n"
ImportError: Matplotlib qt-based backends require an external PyQt4, PyQt5,
PySide or PySide2 package to be installed, but it was not found.
>>>