The following code is based on the Qt Getting Started Programming with Qt Hello Notepad tutorial. There are five parts in all.
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
'''
PyQt4 conversion of Qt Tutorial 'Hello Notepad'
When the user wants to quit an application, you might want to
pop-up a dialog that asks whether he/she really wants to quit.
In this example, we subclass QWidget, and add a slot that we
connect to the Quit button.
NOTES:
=====
The original code defines 'textEdit' as a 'private' variable.
This is simulated here by the underscore in '_textEdit' although
this is only to signal to other developers that the variable
is not meant to be accessed by external classes.
Python, unlike C++ and Java, does not enforce privacy, as is
evident when the 'notepad._textEdit.setText()' method is called in main().
The original code also defines the Quit button variable as private.
Here it is simply defined as a local variable within the __init__
method as it is not called by any of the class methods. Neither
can it be accessed by external methods such as main(); it's scope
(accessibility) is limited to the __init__ method.
User visible strings are wrapped in the 'self.tr()' function
which is provided by QObject, the base class for all Qt objects.
The function makes the strings accessible to the Qt translation
utility 'Qt Linguist'
The 'quit()' method has been renamed 'quit_()' as 'quit' is a
reserved word in Python. Since the method is being used as a
'slot' it has been identified as such using a PyQt4 decorator
which, according to the PyQt4 documentation, will improve
memory performance.
last modified: 2012-01-23 jg
ref:
http://developer.qt.nokia.com/doc/qt-4.8/gettingstartedqt.html
http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/new_style_signals_slots.html
'''
import sys
from PyQt4.QtGui import (QApplication, QTextEdit, QPushButton, QWidget,
QVBoxLayout, QMessageBox)
from PyQt4.QtCore import (pyqtSlot)
class Notepad(QWidget): # subclass QWidget
def __init__(self, parent=None):
super(Notepad, self).__init__(parent) # initialise base (QWidget) class
self._textEdit = QTextEdit()
quitBtn = QPushButton(self.tr("&Quit"))
# connect the quitBtn to this objects quit() method
quitBtn.clicked.connect(self.quit_)
layout = QVBoxLayout()
layout.addWidget(self._textEdit)
layout.addWidget(quitBtn)
self.setLayout(layout)
self.setWindowTitle(self.tr("Notepad"))
@pyqtSlot() # identify this method as a 'slot'
def quit_(self):
msgBox = QMessageBox()
msgBox.setWindowTitle(self.tr("Notepad"))
msgBox.setText(self.tr("Are you sure you want to quit?"))
msgBox.setStandardButtons(QMessageBox.Yes | QMessageBox.No)
msgBox.setDefaultButton(QMessageBox.No)
if msgBox.exec() == QMessageBox.Yes:
QApplication.instance().quit()
def main():
app = QApplication(sys.argv)
notepad = Notepad()
notepad._textEdit.setText("We now inherit QWidget.")
notepad.show()
sys.exit(app.exec_())
if __name__ == '__main__':
main()
