Python: Connect QlineEdit with QlcdNumber via button

Question

Why doesn't the content of the edit box get transferred into the lcdNumber field?

class MainDialog (QDialog, MultiTool_widget_ui.Ui_Form):
    def __init__(self):
        #super(MainDialog, self).__init__() OR <next line>
        QDialog.__init__(self)
        self.setupUi(self)
        self.connect(self.pushButton, SIGNAL("clicked()"),self.lcdNumber.display(self.lineEdit.text()))    

Answer 1

Signals must be connected to a callable object. But in your example:

    self.connect(self.pushButton, SIGNAL("clicked()"),
        self.lcdNumber.display(self.lineEdit.text()))

you are actually passing in the return value of the display() method, which in this case, is None.

To fix your example, you can use a lambda function, like this:

    self.pushButton.clicked.connect(
        lambda: self.lcdNumber.display(self.lineEdit.text()))

Now you are passing in a function object, which will be called when the signal is fired.