Create QT UI In Maya

maya_testUI_qt.py

from PyQt5 import QtWidgets
from PyQt5 import QtCore
from PyQt5 import QtGui

from maya import OpenMayaUI
from sip import wrapinstance

class Test_UI(QtWidgets.QWidget):
    
    def __init__(self, *args, **kwargs):
        
        super(Test_UI, self).__init__(*args, **kwargs)
        
        self.setParent(self.getMainWindow())
        self.setWindowFlags(QtCore.Qt.Window)
        
        self.setObjectName('Test_UI_uniqueId')
        self.setWindowTitle('Test User Interface')
        self.setGeometry(50, 50, 280, 150)
        self.initUI()
        
    def getMainWindow(self):
        
        ptr = OpenMayaUI.MQtUtil.mainWindow()
        mainWindow = wrapinstance(long(ptr), QtWidgets.QWidget)
        
        return mainWindow
        
    def initUI(self):
        
        self.layout = QtWidgets.QGridLayout(self)
        self.setLayout(self.layout)
        
        self.menuBar = QtWidgets.QMenuBar(parent = self.getMainWindow()) # requires parent
        self.menu = QtWidgets.QMenu(self)
        self.menu.setTitle("Menu")
        self.menuBar.addMenu(self.menu)
        self.menu.addAction("Menu Item")
        self.menu.triggered.connect(self.menuAction)
        
        self.text = QtWidgets.QLabel(self)
        self.text.setText("Test Window")
        self.text.setAlignment(QtCore.Qt.AlignCenter)
        
        self.layout.addWidget(self.menuBar, 0, 0, 1, 1)
        self.layout.addWidget(self.text, 0, 0, 1, 1)
        
    def menuAction(self):
        print("Menu Works.")
        
Test_UI().show() # show UI