Added workaround for Qt crash-at-exit bug (make sure that all GraphicsItems live in a scene before exiting)

__init__.py

@@ -119,11 +119,27 @@ from .SignalProxy import *
 from .ptime import time
 
 
+## Workaround for Qt exit crash:
+## ALL QGraphicsItems must have a scene before they are deleted.
+## This is potentially very expensive, but preferred over crashing.
+import atexit
+def cleanup():
+    if QtGui.QApplication.instance() is None:
+        return
+    import gc
+    s = QtGui.QGraphicsScene()
+    for o in gc.get_objects():
+        try:
+            if isinstance(o, QtGui.QGraphicsItem) and o.scene() is None:
+                s.addItem(o)
+        except RuntimeError:  ## occurs if a python wrapper no longer has its underlying C++ object
+            continue
+atexit.register(cleanup)
+
+
 
 ## Convenience functions for command-line use
 
-
-
 plots = []
 images = []
 QAPP = None
@@ -176,8 +192,8 @@ show = image  ## for backward compatibility
     
     
 def mkQApp():
-    if QtGui.QApplication.instance() is None:
     global QAPP
+    if QtGui.QApplication.instance() is None:
         QAPP = QtGui.QApplication([])
-        
+    return QAPP