[Tutor] Self and class functions

[Dave Angel]

On 06/29/2013 06:36 PM, Phil wrote:
> Thank you for reading this.

You should be telling us some things.  I'll guess for you:

You're using Python 3.3 with Qt for a gui, and Linux 12.04 for an OS.

>
> I'm attempting to access the GUI widgets. The buttonClicked slot does
> what I want but I'd like to access the widgets outside of the class. My
> function setLabel doesn't work because self and ui are not known.
>
> I have a second class named Frame that includes a function named dummy.
> Accessing that function is not a problem.

The function is called a method if it's actually part of a class.

You don't show us the code for that class and method.  But according to 
the call below, the method must be a staticmethod or equivalent. 
Perhaps like the following:

class Frame:
     @staticmethod
     def dummy():
         return 42

Static methods are strange because they have no self or cls arguments. 
In other words, they're just ordinary functions which happen to be 
defined inside a class.  So it's in a different namespace, but has no 
special arguments.

The other "strange" method is a classmethod, which takes a cls (class) 
parameter instead of a self parameter.

The methods below are ordinary methods, and thus need a self parameter. 
  Normally that's obtained by creating an instance of the class.


>
> -------------------------------------
>
> from mainwindow import Ui_MainWindow
> from PySide import QtCore, QtGui
> from frame import Frame
>
> class DrawTest(QtGui.QMainWindow):
>      def __init__(self, parent=None):
>          super(DrawTest, self).__init__(parent)
>
>          self.ui = Ui_MainWindow()
>          self.ui.setupUi(self)
>
>      def buttonClicked(self):
>          print("clicked")
>          self.ui.pushButton.setText("test")
>          self.ui.label.setText("Testing")
>
>      def setLabel(self):
>          self.ui.label.setText("Bingo")
>
> DrawTest.setLabel(self)
> DrawTest.ui.label.setText("Bingo")
>
> The two lines above don't work,

You generally should specify in what way they don't work.  In your case 
they don't work because 'self' is unbound in top-level code.  You could 
use self if you were already inside a method of the same class and were 
calling a different one.

> so my question is how do access the
> setText function? And, what do I do about the self parameter in the
> setLabel function?
>

Normally, you create an instance of the class.  For example, you might do:
     mywindow = DrawTest(parent)

Then, now you have the object, you can call the method:

     mywindow.setLabel()


I have no idea about ui.label, I don't know QT.

> Accessing the Frame class is not a problem.
>
> Frame.dummy()
>
> I have spent the better part of a day searching the Internet for an
> answer and I have attempted to find an answer from two other mailing
> lists but they don't entertain low level questions.
>

You need to play with classes using a simple Python tutorial, before you 
try to even understand a GUI.


-- 
DaveA