AttributeError with PySide : can't determine where it comes from

I'm running into a very strange error while using QThread in PySide. As I run my code, when I click on the button that is supposed to launch the thread and send Signal, I get :

AttributeError: 'builtin_function_or_method' object has no attribute 'displayText'

at line :

self.displayMessage.connect(self.window.displayText)

NB : displayText is a method that I defined in my MainWindow(QWidget) class, while displayMessage is the signal to be emitted.

This error seems, according to the Internet, to occur in various situations, and I couldn't find one that suits my case yet. Therefore I have 2 questions :

• Have you guys ever met this error before in a similar situation, and could you (if yes) give me some tips ?
• Am I doing it right ? I can't post my code directly down here, so I created a short verifiable example in which I used the same process. Unfortunately, it seems to work perfectly. Please tell me if at least my construction is correct.

Thank you very much.

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EDIT : I eventually figured out that I have forgotten a self somewhere in my big code, but the actual error was hidden to me behind this one that I didn't know. I'm still interested in whether or not this code is reliable, and am fully open to suggestions of improvement.

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Without thread

When you click "GO !" and try to move the window, you can see that it freezes for a second.

#!/usr/bin/env python
# -*- encoding : utf-8 -*-
import sys
import time
from PySide.QtCore import *
from PySide.QtGui import *

class MainWindow(QWidget):
    def __init__(self, qt_app):
        QWidget.__init__(self)
        worker = Worker(self)
        self.qt_app = qt_app
        self.setGeometry(100, 100, 220, 40)
        self.infoPanel = QTextEdit(self)
        self.infoPanel.setReadOnly(True)
        self.goButton = QPushButton('GO !', self)
        self.goButton.clicked.connect(lambda: worker.displayOnWindow())
        self.layout = QVBoxLayout()
        self.layout.addWidget(self.infoPanel)
        self.layout.addWidget(self.goButton)
        self.setLayout(self.layout)
    def launch(self):
        self.show()
        self.qt_app.exec_()

class Worker():
    def __init__(self, window):
        self.counter = 0
        self.window = window
    def displayOnWindow(self):
        time.sleep(1)
        self.window.infoPanel.append(str(self.counter))
        self.counter += 1

if __name__=='__main__':
    qt_app = QApplication(sys.argv)
    mw = MainWindow(qt_app)
    mw.launch()

With thread

Now you can move the window without trouble, since the sleeping thread is not the one that displays the window. I've written a sub-class for my thread because in the original code there are some functions that will be called by several buttons.

#!/usr/bin/env python
# -*- encoding : utf-8 -*-
import sys
import time
from PySide.QtCore import *
from PySide.QtGui import *

class MainWindow(QWidget):
    def __init__(self, qt_app):
        QWidget.__init__(self)
        worker = SubWorker(self)
        self.qt_app = qt_app
        self.setGeometry(100, 100, 220, 40)
        self.infoPanel = QTextEdit(self)
        self.infoPanel.setReadOnly(True)
        self.goButton = QPushButton('GO !', self)
        self.goButton.clicked.connect(lambda: worker.start())
        self.layout = QVBoxLayout()
        self.layout.addWidget(self.infoPanel)
        self.layout.addWidget(self.goButton)
        self.setLayout(self.layout)
    def launch(self):
        self.show()
        self.qt_app.exec_()
    @Slot(int)
    def displayOnWindow(self, i):
        self.infoPanel.append(str(i))

class Worker(QThread):
    displayMessage = Signal(int)
    def __init__(self, window):
        QThread.__init__(self)
        self.counter = 0
        self.window = window
        self.displayMessage.connect(self.window.displayOnWindow)
    def run(self, *args, **kwargs):
        return QThread.run(self, *args, **kwargs)

class SubWorker(Worker):
    def __init__(self, window):
        Worker.__init__(self, window)
    def run(self):
        time.sleep(1)
        self.displayMessage.emit(self.counter)
        self.counter += 1

if __name__=='__main__':
    qt_app = QApplication(sys.argv)
    mw = MainWindow(qt_app)
    mw.launch()