CODEWITHSUNDEEP
pythonclassvariablesinstance
Alexander Pope
Alexander Pope

Reputation: 1224

Python variable "declaration" in function body

class Example(wx.Frame):

    def __init__(self, *args, **kwargs):
        super(Example, self).__init__(*args, **kwargs) 

        self.InitUI()

    def InitUI(self):    

        menubar = wx.MenuBar()
        fileMenu = wx.Menu()
        viewMenu = wx.Menu()

        self.shst = viewMenu.Append(wx.ID_ANY, 'Show statubar', 
            'Show Statusbar', kind=wx.ITEM_CHECK)
...

I've recently started learning python and wxPython. The above code snipppet is from http://www.zetcode.com/wxpython/menustoolbars/ . I'm trying to get my head around the self.shst variable. Why is it necessary to prefix it with the self keyword ?

From what I read, the self keyword is used in that context in the __init__ method, to "declare" instance variables, but the author has no shst declaration in __init__

Edit In light of your answers I did the following test:

class Test(object):
    def __init__(self):
        self.x = 20
    def func(self):
        self.y = 10
    def getVal(self):
        return self.y


def main():
    t = Test()
    print t.getVal()
    print dir(t)

if __name__ == '__main__':
    main()

I am unable to access self.y in the getVal() function, and I don't see y in the output from dir(t). Shouldn't self.y be accessible to every function in the Test class ?

Upvotes: 0

Views: 250

Answers (2)

bogatron
bogatron

Reputation: 19169

If you did not prefix shst with self., then it would just be a local variable that goes out of scope and is garbage-collected after the method exits. There is no need to declare python class/object members prior to assignment.

Upvotes: 1

Daniel Roseman
Daniel Roseman

Reputation: 599530

There's no necessity to define instance variables in __init__. They can be defined anywhere. Python is a dynamic langauge, and it is possible to add attributes to an object at any point.

Upvotes: 1

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