PySide2: A QFileDialog displayed modally can not be closed by triggering accept().

repro_PySide2_modal_QFileDialog_ignores_accept.py

# -*- coding: utf-8 -*-

# try to import PySide2, fall back to PySide
try:
    from PySide2 import QtCore, QtGui, QtWidgets
except ImportError:
    from PySide import QtCore, QtGui
    import PySide.QtGui as QtWidgets

import sys
import os
import tempfile
import shutil


# -----------------------------------------------------------------------------
def repro():
    """Creates a FileDialog and displays it modally.

    Using a QTimer the FileDialog should automatically get closed after
    3 seconds by triggering the slot 'accept()'.

    This works (on Windows 10):
        - in standalone Python 2.7 + PySide 
        - in Maya 2016 SP6 (--> PySide)

    This does not work: (tested on Windows 10) 
        - in Maya 2017 Update4 (--> PySide2).
        - in Maya 2018 Update2 (--> PySide2).

    """
    parent_widget = _resolveParentWidget()

    # creates a FileDialog in save mode and
    # points it to a valid temp directory
    temp_dir = tempfile.mkdtemp()
    file_dialog = QtWidgets.QFileDialog(parent=parent_widget,
                                        directory=temp_dir)
    file_dialog.selectFile('saveName')
    file_dialog.setAcceptMode(QtWidgets.QFileDialog.AcceptSave)


    # trigger 'accept' after 3 seconds

    def triggerAccept():
        file_dialog.accept()
        # proof that QTimer is working and this got executed
        print 'triggerAccept got called'

    # QtCore.QTimer.singleShot(3000, file_dialog.accept)
    QtCore.QTimer.singleShot(3000, triggerAccept)

    print '- displaying QFileDialog modally.'
    print '- triggering "accept()" after 3 seconds.'
    status = file_dialog.exec_()
    print '- return value: %s  (expected:  1)' % status

    # cleanup 
    file_dialog = None
    shutil.rmtree(temp_dir)


# -----------------------------------------------------------------------------
def _resolveParentWidget():
    """Resolves and returns context-specific parent widget.

    In a standalone Python context a QApplication gets created 
    and None gets returned.

    In a Maya context the Main Maya Window gets returned. 

    """
    context = os.path.basename(sys.executable).lower()

    if context.find('python') != -1:
       app = QtWidgets.QApplication(sys.argv)
       return None

    elif context.find('maya') != -1:
        for widget in QtWidgets.QApplication.topLevelWidgets():
            name = widget.objectName()
            if name == 'MayaWindow':
                return widget
    
    else:
        raise NotImplementedError('Context not supported: %s' % context)


if __name__ == '__main__':
    repro()
    

I stumbled over this issue while writing tests for some UI code.
I want to display a QDialog modally and then automatically close it with a few seconds delay by calling accept().
This does work as expected in PySide -- however it does not work anymore in PySide2.

In PySide (both Standalone Python 2.7 and Maya 2016 SP6) I can:

1.) create a QFileDialog
2.) set up a QTimer to call accept() with a few seconds delay
3.) display it modally by calling exec_()

The expected result of this is that the QFileDialog gets displayed modally and then gets closed by the delayed call to accept().
The return value of the exec_() call will be '1' as expected.

In PySide2 (Maya 2017 & Maya 2018) this does not work...

• the QFileDialog gets displayed modally.
• the QTimer gets executed (verified by a print message)
• however the accept() call gets ignored. The QFileDialog remains open until I manually click the OK button.

Repro:

1.) Download the provided Gist Python file.

2.) Execute it in a PySide environment (either standalone Python 2.7 + PySide, or in the Script Editor of Maya 2016)
--> this works as expected

3.) Now execute it in a PySide2 environment (in the Script Editor of Maya 2017 or Maya 2018)
--> this does not work