While I was trying to write a PyQt4 loadUi() equivalent, it seems
the QUiLoader.createWidget() returns QWidget for all widgets
instead of instances of className class.

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from PySide import QtCore
from PySide.QtUiTools import QUiLoader

class MyQUiLoader(QUiLoader):
    def __init__(self, baseinstance):
        QUiLoader.__init__(self)
        self.baseinstance = baseinstance

    def createWidget(self, className, parent=None, name=""):
        widget = QUiLoader.createWidget(self, className, parent, name)
        print className, parent, name, widget, widget.metaObject().className() 
        if parent is None:
            return self.baseinstance
        else:
            setattr(self.baseinstance, name, widget)
            return widget

def loadUi(uifile, baseinstance=None):
    loader = MyQUiLoader(baseinstance)
    ui = loader.load(uifile)
    QtCore.QMetaObject.connectSlotsByName(ui)
    print ui.__dict__
    return ui