Do not store a reference to the main window in sys.excepthook

src/calibre/gui2/lrf_renderer/main.py

@@ -312,7 +312,7 @@ def main(args=sys.argv, logger=None):
         opts = normalize_settings(parser, opts)
         stream = open(args[1], 'rb') if len(args) > 1 else None
         main = file_renderer(stream, opts, logger=logger)
-        sys.excepthook = main.unhandled_exception
+        main.set_exception_handler()
         main.show()
         main.render()
         main.activateWindow()

src/calibre/gui2/main.py

@@ -222,7 +222,7 @@ class GuiRunner(QObject):
             prints('Started up in %.2f seconds'%(time.time() -
                 self.startup_time), 'with', len(db.data), 'books')
         add_filesystem_book = partial(main.iactions['Add Books'].add_filesystem_book, allow_device=False)
-        sys.excepthook = main.unhandled_exception
+        main.set_exception_handler()
         if len(self.args) > 1:
             files = [os.path.abspath(p) for p in self.args[1:] if not
                     os.path.isdir(p)]

src/calibre/gui2/main_window.py

@@ -5,7 +5,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
 
 
-import StringIO, traceback, sys, gc
+import StringIO, traceback, sys, gc, weakref
 
 from PyQt5.Qt import (QMainWindow, QTimer, QAction, QMenu, QMenuBar, QIcon,
                       pyqtSignal, QObject)
@@ -68,6 +68,18 @@ class GarbageCollector(QObject):
         for obj in gc.garbage:
             print (obj, repr(obj), type(obj))
 
+class ExceptionHandler(object):
+
+    def __init__(self, main_window):
+        self.wref = weakref.ref(main_window)
+
+    def __call__(self, type, value, tb):
+        mw = self.wref()
+        if mw is not None:
+            mw.unhandled_exception(type, value, tb)
+        else:
+            sys.__excepthook__(type, value, tb)
+
 class MainWindow(QMainWindow):
 
     ___menu_bar = None
@@ -115,6 +127,9 @@ class MainWindow(QMainWindow):
         else:
             gc.enable() if enabled else gc.disable()
 
+    def set_exception_handler(self):
+        sys.excepthook = ExceptionHandler(self)
+
     def unhandled_exception(self, type, value, tb):
         if type == KeyboardInterrupt:
             self.keyboard_interrupt.emit()

src/calibre/gui2/tweak_book/main.py

@@ -69,7 +69,7 @@ def _run(args, notify=None):
     Application.setOrganizationName(ORG_NAME)
     Application.setApplicationName(APP_UID)
     main = Main(opts, notify=notify)
-    sys.excepthook = main.unhandled_exception
+    main.set_exception_handler()
     main.show()
     if len(args) > 1:
         main.boss.open_book(args[1], edit_file=args[2:], clear_notify_data=False)

src/calibre/gui2/viewer/main.py

@@ -1187,8 +1187,7 @@ def main(args=sys.argv):
     # turn_off_internal_scrollbars does not take effect for the first
     # rendered document
     main.view.load_path(P('viewer/blank.html', allow_user_override=False))
-
+    main.set_exception_handler()
-    sys.excepthook = main.unhandled_exception
     main.show()
     if opts.raise_window:
         main.raise_()