Set icon properly for macOS

On most platforms, windows have their own icons that are displayed in conjunction with windows. On macOS, icons are used differently. Individual windows should not have an icon unless they are associated with a file. On the other hand, processes ("Apps") have icons that can be set.

If Matplotlib is running a FigureManagerBase, then we can assume that Matplotlib can be responsible for setting the process icon.

Author: joelfrederico

lib/matplotlib/backends/backend_qt.py

@@ -1,7 +1,6 @@
 import functools
 import operator
 import os
-import signal
 import sys
 import traceback
 
@@ -121,6 +120,10 @@ def _create_qApp():
             except AttributeError:  # Only for Qt>=5.14.
                 pass
             qApp = QtWidgets.QApplication(["matplotlib"])
+            if sys.platform == "darwin":
+                image = str(cbook._get_data_path('images/matplotlib.svg'))
+                icon = QtGui.QIcon(image)
+                qApp.setWindowIcon(icon)
             qApp.lastWindowClosed.connect(qApp.quit)
             cbook._setup_new_guiapp()
         else:
@@ -519,8 +522,10 @@ def __init__(self, canvas, num):
         self.window.closing.connect(canvas.close_event)
         self.window.closing.connect(self._widgetclosed)
 
-        image = str(cbook._get_data_path('images/matplotlib.svg'))
-        self.window.setWindowIcon(QtGui.QIcon(image))
+        if sys.platform != "darwin":
+            image = str(cbook._get_data_path('images/matplotlib.svg'))
+            icon = QtGui.QIcon(image)
+            self.window.setWindowIcon(icon)
 
         self.window._destroying = False