Add a QMenuBar to a QWidget

Question

I'm trying to integrate a QMenubar in a QWidget in Pyside2 in Python3. It seems to be easier to integrate a QMenubar to a QMainWindow but I started the project with a QWidget and not a QMainWindow and this is why I would like to have a solution for a QWidget.

When I run the code, there is no error message but the menubar doesn't appear when I run the app. I checked that stackoveflow page but it didn't help me or I wasn't able to implement it.

Code

from PySide2.QtWidgets import (QWidget, QApplication, QGraphicsView, 
QGridLayout)
from PySide2 import QtCore, QtWidgets, QtGui
from PySide2.QtOpenGL import *
from PySide2.QtCore import *
from PySide2.QtGui import *

image_path_str='image.jpg'

class View(QGraphicsView):
    photo_clicked = QtCore.Signal(QtCore.QPoint)

    def __init__(self, parent):
        super(View, self).__init__()
        self.scene = QtWidgets.QGraphicsScene(self)
        self.photo = QtWidgets.QGraphicsPixmapItem()
        self.scene.addItem(self.photo)
        self.pixmap = QtGui.QPixmap(image_path_str)
        self.photo.setPixmap(self.pixmap)
        self.setScene(self.scene)
        self.setDragMode(QGraphicsView.ScrollHandDrag)

class Window(QWidget):
    def __init__(self):
        super(Window, self).__init__()
        self.view = View(self)

        self.layout_contain_P1_P2 = QtWidgets.QGridLayout()
        self.checkbox_P1= QtWidgets.QCheckBox("P1",self)
        self.line_edit_P1_x = QtWidgets.QLineEdit(self)
        self.line_edit_P1_x.setReadOnly(True)
        self.line_edit_P1_y = QtWidgets.QLineEdit(self)
        self.line_edit_P1_y.setReadOnly(True)

        self.menubar = QtWidgets.QMenuBar()
        self.archive = self.menubar.addMenu("archive")
        self.menubar.setObjectName("menubar")

        self.layout_contain_P1_P2.addWidget(self.checkbox_P1, 0, 0, Qt.AlignLeft)

        self.grid_layout_P1_x_y = QtWidgets.QGridLayout()
        self.grid_layout_P1_x_y.addWidget(self.line_edit_P1_x, 1, 0, Qt.AlignLeft)
        self.grid_layout_P1_x_y.addWidget(self.line_edit_P1_y, 2, 0, Qt.AlignLeft)

        self.layout_contain_P1_P2.addLayout(self.grid_layout_P1_x_y, 0, 1, 1, 1)
        self.checkbox_P2 = QtWidgets.QCheckBox("P2",self)
        self.line_edit_P2_x = QtWidgets.QLineEdit(self)
        self.line_edit_P2_x.setReadOnly(True)
        self.line_edit_P2_y = QtWidgets.QLineEdit(self)
        self.line_edit_P2_y.setReadOnly(True)

        self.layout_contain_P1_P2.addWidget(self.checkbox_P2, 1, 0, Qt.AlignLeft)
        self.grid_layout_P2_x_y = QtWidgets.QGridLayout()

        self.grid_layout_P2_x_y.addWidget(self.line_edit_P2_x, 0, 0, Qt.AlignLeft)
        self.grid_layout_P2_x_y.addWidget(self.line_edit_P2_y, 1, 0, Qt.AlignLeft)

        self.layout_contain_P1_P2.addLayout(self.grid_layout_P2_x_y, 1, 1, Qt.AlignLeft)

        self.combo_box1 = QtWidgets.QComboBox(self)
        self.combo_box1.addItem("measurements set 1")
        self.combo_box1.addItem("measurements set 1")

        self.combo_box2 = QtWidgets.QComboBox(self)
        self.combo_box2.addItem("P1-P2")
        self.combo_box2.addItem("P3-P4")

        self.vertical1= QtWidgets.QVBoxLayout()

        self.vertical1.addWidget(self.menubar)
        self.vertical1.addWidget(self.combo_box1)
        self.vertical1.addWidget(self.combo_box2)
        self.vertical1.addLayout(self.layout_contain_P1_P2)

        self.vertical2= QtWidgets.QVBoxLayout()
        self.vertical2.addWidget(self.view)

        self.horizontal= QtWidgets.QHBoxLayout()
        self.horizontal.addLayout(self.vertical1)
        self.horizontal.addLayout(self.vertical2)

        self.setLayout(self.horizontal)
        self.setWindowTitle("Image viewer")
        self.setGeometry(200, 200, 1000, 800)

app = QApplication.instance()
if app is None:
        app = QApplication([])
w = Window()
w.show()
w.raise_()
QApplication.setOverrideCursor(QCursor(Qt.CrossCursor))
app.exec_()

Here is screenshot of what I get:

Edit : not optimal workaround: add a QMainWindow class

Here is not optimal workaround. I had to add an extra class QMainWindow and call the Widget from within the QMainWindow

from PySide2.QtWidgets import (QWidget, QApplication, QGraphicsView,
QGridLayout, QMainWindow, QAction, QMenu)
from PySide2 import QtCore, QtWidgets, QtGui
from PySide2.QtOpenGL import *
from PySide2.QtCore import *
from PySide2.QtGui import *

image_path_str='image.jpg'

class View(QGraphicsView):
    photo_clicked = QtCore.Signal(QtCore.QPoint)

    def __init__(self, parent):
        super(View, self).__init__()
        self.scene = QtWidgets.QGraphicsScene(self)
        self.photo = QtWidgets.QGraphicsPixmapItem()
        self.scene.addItem(self.photo)
        self.pixmap = QtGui.QPixmap(image_path_str)
        self.photo.setPixmap(self.pixmap)
        self.setScene(self.scene)
        self.setDragMode(QGraphicsView.ScrollHandDrag)

class Window(QWidget):
    def __init__(self):
        super(Window, self).__init__()
        self.view = View(self)

        self.layout_contain_P1_P2 = QtWidgets.QGridLayout()
        self.checkbox_P1= QtWidgets.QCheckBox("P1",self)
        self.line_edit_P1_x = QtWidgets.QLineEdit(self)
        self.line_edit_P1_x.setReadOnly(True)
        self.line_edit_P1_y = QtWidgets.QLineEdit(self)
        self.line_edit_P1_y.setReadOnly(True)

        self.layout_contain_P1_P2.addWidget(self.checkbox_P1, 0, 0, Qt.AlignLeft)

        self.grid_layout_P1_x_y = QtWidgets.QGridLayout()
        self.grid_layout_P1_x_y.addWidget(self.line_edit_P1_x, 1, 0, Qt.AlignLeft)
        self.grid_layout_P1_x_y.addWidget(self.line_edit_P1_y, 2, 0, Qt.AlignLeft)

        self.layout_contain_P1_P2.addLayout(self.grid_layout_P1_x_y, 0, 1, 1, 1)
        self.checkbox_P2 = QtWidgets.QCheckBox("P2",self)
        self.line_edit_P2_x = QtWidgets.QLineEdit(self)
        self.line_edit_P2_x.setReadOnly(True)
        self.line_edit_P2_y = QtWidgets.QLineEdit(self)
        self.line_edit_P2_y.setReadOnly(True)

        self.layout_contain_P1_P2.addWidget(self.checkbox_P2, 1, 0, Qt.AlignLeft)
        self.grid_layout_P2_x_y = QtWidgets.QGridLayout()

        self.grid_layout_P2_x_y.addWidget(self.line_edit_P2_x, 0, 0, Qt.AlignLeft)
        self.grid_layout_P2_x_y.addWidget(self.line_edit_P2_y, 1, 0, Qt.AlignLeft)

        self.layout_contain_P1_P2.addLayout(self.grid_layout_P2_x_y, 1, 1, Qt.AlignLeft)

        self.combo_box1 = QtWidgets.QComboBox(self)
        self.combo_box1.addItem("measurements set 1")
        self.combo_box1.addItem("measurements set 1")

        self.combo_box2 = QtWidgets.QComboBox(self)
        self.combo_box2.addItem("P1-P2")
        self.combo_box2.addItem("P3-P4")

        self.vertical1= QtWidgets.QVBoxLayout()

        # self.vertical1.addWidget(self.menubar)
        self.vertical1.addWidget(self.combo_box1)
        self.vertical1.addWidget(self.combo_box2)
        self.vertical1.addLayout(self.layout_contain_P1_P2)

        self.vertical2= QtWidgets.QVBoxLayout()
        self.vertical2.addWidget(self.view)

        self.horizontal= QtWidgets.QHBoxLayout()
        self.horizontal.addLayout(self.vertical1)
        self.horizontal.addLayout(self.vertical2)

        self.setLayout(self.horizontal)
        self.setWindowTitle("Image viewer")
        self.setGeometry(200, 200, 1000, 800)

class Main_window(QMainWindow):

    def __init__(self, parent=None):

        super(Main_window, self).__init__(parent)
        self.window = Window()
        self.setCentralWidget(self.window)
        self.initUI()

    def initUI(self):

        menubar = self.menuBar()
        fileMenu = menubar.addMenu('File')

        impMenu = QMenu('Import', self)
        impAct = QAction('Import mail', self)
        impMenu.addAction(impAct)

        newAct = QAction('New', self)

        fileMenu.addAction(newAct)
        fileMenu.addMenu(impMenu)


app = QApplication.instance()
if app is None:
        app = QApplication([])
mw = Main_window()
mw.show()
mw.raise_()
QApplication.setOverrideCursor(QCursor(Qt.CrossCursor))
app.exec_()