backend_qt4: avoid a crash at exit with PySide. Closes #551.

mdboom · mdboom · commit bb9946260e44 · 2011-10-25T09:50:27.000-04:00
diff --git a/lib/matplotlib/backends/backend_qt4.py b/lib/matplotlib/backends/backend_qt4.py
@@ -361,6 +361,8 @@ def show(self):
         self.window.show()
 
     def destroy( self, *args ):
+        # check for qApp first, as PySide deletes it in its atexit handler
+        if QtGui.QApplication.instance() is None: return
         if self.window._destroying: return
         self.window._destroying = True
         QtCore.QObject.disconnect( self.window, QtCore.SIGNAL( 'destroyed()' ),
