Merge pull request #1 from oliveroxtoby/matplotlib_import_issue

Prevent matplotlib selecting the PyQt API instead of PySide2

src/Mod/Plot/Plot.py

@@ -26,11 +26,20 @@ import FreeCAD
 import PySide
 from PySide import QtCore, QtGui
 from distutils.version import LooseVersion as V
+import sys
 
 try:
     import matplotlib
     matplotlib.use('Qt5Agg')
+    
+    # Force matplotlib to use PySide backend by temporarily unloading PyQt
+    if 'PyQt5.QtCore' in sys.modules:
+        del sys.modules['PyQt5.QtCore']
         import matplotlib.pyplot as plt
+        import PyQt5.QtCore
+    else:
+        import matplotlib.pyplot as plt
+
     from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
     from matplotlib.backends.backend_qt5agg import NavigationToolbar2QT as NavigationToolbar