Complete newbie hello world question!

[adamsp303]

I am using PyQT and am trying to set up a really simple program. All I want is a simple button that when clicked changes a label text to hello world.. Sorry if this is the wrong place to ask this question.. I have designed the UI in QT 4 Designer and am editing the code in Eric.

The UI code is:

# -*- coding: utf-8 -*-
 
# Form implementation generated from reading ui file 'test.ui'
#
# Created: Sat Jan 26 21:56:01 2013
#      by: PyQt4 UI code generator 4.9.1
#
# WARNING! All changes made in this file will be lost!
 
from PyQt4 import QtCore, QtGui
 
try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    _fromUtf8 = lambda s: s
 
class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName(_fromUtf8("Form"))
        Form.resize(247, 177)
        self.label = QtGui.QLabel(Form)
        self.label.setGeometry(QtCore.QRect(60, 40, 131, 20))
        self.label.setObjectName(_fromUtf8("label"))
        self.button = QtGui.QPushButton(Form)
        self.button.setGeometry(QtCore.QRect(70, 100, 96, 27))
        self.button.setObjectName(_fromUtf8("button"))
 
        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)
 
    def retranslateUi(self, Form):
        Form.setWindowTitle(QtGui.QApplication.translate("Form", "Form", None, QtGui.QApplication.UnicodeUTF8))
        self.label.setText(QtGui.QApplication.translate("Form", "Hmmm...", None, QtGui.QApplication.UnicodeUTF8))
        self.button.setText(QtGui.QApplication.translate("Form", "Press Me!", None, QtGui.QApplication.UnicodeUTF8))

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'test.ui'
#
# Created: Sat Jan 26 21:56:01 2013
#      by: PyQt4 UI code generator 4.9.1
#
# WARNING! All changes made in this file will be lost!

from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    _fromUtf8 = lambda s: s

class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName(_fromUtf8("Form"))
        Form.resize(247, 177)
        self.label = QtGui.QLabel(Form)
        self.label.setGeometry(QtCore.QRect(60, 40, 131, 20))
        self.label.setObjectName(_fromUtf8("label"))
        self.button = QtGui.QPushButton(Form)
        self.button.setGeometry(QtCore.QRect(70, 100, 96, 27))
        self.button.setObjectName(_fromUtf8("button"))

        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)

    def retranslateUi(self, Form):
        Form.setWindowTitle(QtGui.QApplication.translate("Form", "Form", None, QtGui.QApplication.UnicodeUTF8))
        self.label.setText(QtGui.QApplication.translate("Form", "Hmmm...", None, QtGui.QApplication.UnicodeUTF8))
        self.button.setText(QtGui.QApplication.translate("Form", "Press Me!", None, QtGui.QApplication.UnicodeUTF8))

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and the main app code is:

import sys
from PyQt4 import QtCore, QtGui
 
import ui_test
 
def clicked():
    designed.label.setText("Hello World!")
 
def main():
    app = QtGui.QApplication(sys.argv)
    designed = ui_test.Ui_Form()
    widget = QtGui.QWidget()
    designed.setupUi(widget)
    designed.button.clicked.connect(clicked) 
    widget.show()
    sys.exit(app.exec_())
 
if __name__ == '__main__':
    main()

import sys
from PyQt4 import QtCore, QtGui

import ui_test

def clicked():
    designed.label.setText("Hello World!")
    
def main():
    app = QtGui.QApplication(sys.argv)
    designed = ui_test.Ui_Form()
    widget = QtGui.QWidget()
    designed.setupUi(widget)
    designed.button.clicked.connect(clicked) 
    widget.show()
    sys.exit(app.exec_())
    
if __name__ == '__main__':
    main()

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But when I run the program and click the button I get the error message:

The debugged program raised the exception unhandled NameError
"global name 'designed' is not defined"
File: /home/peter/Documents/qt/test/app.py, Line: 7
Break here?

So I guess its this line that is causing the problem..

designed.label.setText("Hello World!")

designed.label.setText("Hello World!")

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Can anyone help please

[wysota]

Your "clicked" function doesn't know anything about a "designed" object created in another function. This is a strictly python issue and nothing to do with Qt.

---

Added after 7 minutes:

One possibility to work around it is to define a function in Ui_Form and call that as a slot. Note the code below is sort of a hack that uses some features unique to Python. Usually you'd subclass QWidget, in the constructor instantiate Ui_Form and define the slot function in the QWidget subclass and not the Ui_Form class itself.

def fun_myClickHandler(self):
    self.label.setText("Hello World!")
 
ui_test.Ui_Form.myClickHandler = fun_myClickHandler
 
designed = ui_test.Ui_Form()
widget = QtGui.QWidget()
designed.setupUi(widget)
designed.button.clicked.connect(designed.myClickHandler)
# and so on...

def fun_myClickHandler(self):
    self.label.setText("Hello World!")

ui_test.Ui_Form.myClickHandler = fun_myClickHandler

designed = ui_test.Ui_Form()
widget = QtGui.QWidget()
designed.setupUi(widget)
designed.button.clicked.connect(designed.myClickHandler)
# and so on...

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[adamsp303]

Thank you, got this working now with the following code:

import sys
from PyQt4 import QtCore, QtGui
 
import ui_test
 
def fun_myClickHandler(self):
    self.label.setText("Hello World!")
 
def main():
    ui_test.Ui_Form.myClickHandler = fun_myClickHandler
    app = QtGui.QApplication(sys.argv)
    designed = ui_test.Ui_Form()
    widget = QtGui.QWidget()
    designed.setupUi(widget)
    designed.button.clicked.connect(designed.myClickHandler)
    widget.show()
    sys.exit(app.exec_())
 
if __name__ == '__main__':
    main()
sys.exit(app.exec_())

import sys
from PyQt4 import QtCore, QtGui
     
import ui_test

def fun_myClickHandler(self):
    self.label.setText("Hello World!")
     
def main():
    ui_test.Ui_Form.myClickHandler = fun_myClickHandler
    app = QtGui.QApplication(sys.argv)
    designed = ui_test.Ui_Form()
    widget = QtGui.QWidget()
    designed.setupUi(widget)
    designed.button.clicked.connect(designed.myClickHandler)
    widget.show()
    sys.exit(app.exec_())
     
if __name__ == '__main__':
    main()
sys.exit(app.exec_())

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Although I don't really understand it, I think I need to learn Python :-).. I have been aproaching this from a perspective of wishing to learn to code GUI software and to find an equivalent of visual basic under Linux as its all I have really done before..

[wysota]

Hard to do that without learning a programming language first.