from PySide import QtCore, QtGui, QtUiTools

import sys

class MyWidget(QtGui.QWidget):
    def __init__(self, parent=None):
        super(MyWidget, self).__init__(parent)

if __name__ == '__main__':
    application = QtGui.QApplication(sys.argv)

    loader = QtUiTools.QUiLoader()
    loader.registerCustomWidget(MyWidget)
    print loader.availableWidgets()
    print loader.createWidget('QLabel')
    print loader.createWidget('MyWidget')