main: show error message for uncaught exceptions

src/main/python/main.py

@@ -1,5 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
+import traceback
 
+from PyQt5 import QtWidgets, QtCore
+from PyQt5.QtCore import pyqtSignal
 from fbs_runtime.application_context.PyQt5 import ApplicationContext
 
 import sys
@@ -7,8 +10,48 @@ import sys
 from main_window import MainWindow
 from constants import WINDOW_WIDTH, WINDOW_HEIGHT
 
+
+# http://timlehr.com/python-exception-hooks-with-qt-message-box/
+def show_exception_box(log_msg):
+    if QtWidgets.QApplication.instance() is not None:
+        errorbox = QtWidgets.QMessageBox()
+        errorbox.setText(log_msg)
+        errorbox.exec_()
+
+
+class UncaughtHook(QtCore.QObject):
+    _exception_caught = pyqtSignal(object)
+
+    def __init__(self, *args, **kwargs):
+        super(UncaughtHook, self).__init__(*args, **kwargs)
+
+        # this registers the exception_hook() function as hook with the Python interpreter
+        sys._excepthook = sys.excepthook
+        sys.excepthook = self.exception_hook
+
+        # connect signal to execute the message box function always on main thread
+        self._exception_caught.connect(show_exception_box)
+
+    def exception_hook(self, exc_type, exc_value, exc_traceback):
+        if issubclass(exc_type, KeyboardInterrupt):
+            # ignore keyboard interrupt to support console applications
+            sys.__excepthook__(exc_type, exc_value, exc_traceback)
+        else:
+            log_msg = '\n'.join([''.join(traceback.format_tb(exc_traceback)),
+                                 '{0}: {1}'.format(exc_type.__name__, exc_value)])
+
+            # trigger message box show
+            self._exception_caught.emit(log_msg)
+        sys._excepthook(exc_type, exc_value, exc_traceback)
+
+
+# create a global instance of our class to register the hook
+qt_exception_hook = UncaughtHook()
+
+
 if __name__ == '__main__':
     appctxt = ApplicationContext()       # 1. Instantiate ApplicationContext
+    qt_exception_hook = UncaughtHook()
     window = MainWindow()
     window.resize(WINDOW_WIDTH, WINDOW_HEIGHT)
     window.show()