Error message: "Error: Insufficient arguments"
It is in the qml part at this line:
helloText.text = changeText.doChange()

main.py
@
#!/usr/bin/python2.7

Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).

All rights reserved.

Contact: PySide Team (pyside at openbossa.org)

This file is part of the examples of PySide: Python for Qt.

...

$QT_END_LICENSE$

from PySide import QtCore, QtGui, QtDeclarative

class RotateValue(QtCore.QObject):
def init(self):
super(RotateValue,self).init()
self.r = 0

QtCore.Slot(result=int)
def val(self):

self.r = self.r + 90
return self.r

class ChangeText(QtCore.QObject):
def init(self):
super(ChangeText,self).init()
self.s = "Hi"

# if a slot returns a value the return value type must be explicitly
# defined in the decorator
QtCore.Slot("QString")
def doChange(self):
    return self.s

if name == 'main':
import sys

app = QtGui.QApplication(sys.argv)

view = QtDeclarative.QDeclarativeView()

rotatevalue = RotateValue()
changeText = ChangeText()
timer = QtCore.QTimer()
timer.start(2000)

conrotate = view.rootContext()
conrotate.setContextProperty("rotatevalue", rotatevalue)

context = view.rootContext()
context.setContextProperty("changeText", changeText)
view.setSource(QtCore.QUrl('view.qml'))
view.show()

sys.exit(app.exec_())

@

view.qml

@/*
** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: PySide Team (pyside at openbossa.org)
**
** This file is part of the examples of PySide: Python for Qt.
...
$QT_END_LICENSE$
*/

import Qt 4.7

Rectangle {
id: page

width: 500; height: 200
color: "lightgray"

Text {
    id: helloText
    text: "Hello world!"
    anchors.horizontalCenter: page.horizontalCenter
    y: 30
    font.pointSize: 24; font.bold: true
}


Rectangle {
    id: button
    width: 150; height: 40
    color: "darkgray"
    anchors.horizontalCenter: page.horizontalCenter
    y: 120
    MouseArea {
        id: buttonMouseArea
        objectName: "buttonMouseArea"
        anchors.fill: parent
        onClicked: {
            helloText.rotation = rotatevalue.val()

// next line generates the error
helloText.text = changeText.doChange()
}
}
Text {
id: buttonText
text: "Press me!"
anchors.horizontalCenter: button.horizontalCenter
anchors.verticalCenter: button.verticalCenter
font.pointSize: 16;
}
}
}@