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Use self when:you define an instance method, since it is passed automatically as the first parameter when the method is called; you reference a class or an instance attribute from inside an instance method; you want to refer to instance variables and methods from other instance methods.
self is always required when referring to the instance itself, except when calling the base class constructor (wx. Frame. __init__). All the other variables that you see in the examples (panel, basicLabel, basicText, ...) are just local variables - not related to the current object at all.
If there was no self argument, the same class couldn't hold the information for both these objects. However, since the class is just a blueprint, self allows access to the attributes and methods of each object in python. This allows each object to have its own attributes and methods.
Class methods don't need a class instance. They can't access the instance ( self ) but they have access to the class itself via cls . Static methods don't have access to cls or self . They work like regular functions but belong to the class's namespace.
I have been using classes for only a short while and when I write a method, I make all variables reference self, e.g. self.foo.
However, I'm looking through the wxPython in Action book and notice that "self" isn't used all the time. For example:
import wx
class TextFrame(wx.Frame):
def __init__(self):
wx.Frame.__init__(self, None, -1, 'Text Entry Example',
size=(300, 100))
panel = wx.Panel(self, -1)
basicLabel = wx.StaticText(panel, -1, "Basic Control:")
basicText = wx.TextCtrl(panel, -1, "I've entered some text!",
size=(175, -1))
basicText.SetInsertionPoint(0)
pwdLabel = wx.StaticText(panel, -1, "Password:")
pwdText = wx.TextCtrl(panel, -1, "password", size=(175, -1),
style=wx.TE_PASSWORD)
sizer = wx.FlexGridSizer(cols=2, hgap=6, vgap=6)
sizer.AddMany([basicLabel, basicText, pwdLabel, pwdText])
panel.SetSizer(sizer)
The one below does use "self".
import wx
class ButtonFrame(wx.Frame):
def __init__(self):
wx.Frame.__init__(self, None, -1, 'Button Example',
size=(300, 100))
panel = wx.Panel(self, -1)
self.button = wx.Button(panel, -1, "Hello", pos=(50, 20))
self.Bind(wx.EVT_BUTTON, self.OnClick, self.button)
self.button.SetDefault()
def OnClick(self, event):
self.button.SetLabel("Clicked")
If I remember correctly, "self" is reference to a particular instance of the class, so when is it not necessary? Is there a general rule of thumb?
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