The menu bar in this script doesn't display. It *does* display if QMenuBar is created without a reference to its parent. This bug has been reported at https://bugreports.qt-project.org/browse/PYSIDE-21?focusedCommentId=195277&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-195277

pyside_menu_bug.py

from PySide import QtCore, QtGui

app = QtGui.QApplication([''])

mw = QtGui.QMainWindow()

#mbar = QtGui.QMenuBar()     # menu visible                                     
mbar = QtGui.QMenuBar(mw)  # menu not visible                                   

menu = QtGui.QMenu(mbar)
menu.setTitle("Testing")
mbar.addMenu(menu)
mw.setMenuBar(mbar)

mw.show()
mw.raise_()
app.exec_()