self argument

[Gregoire Welraeds]

In reply to the message of James Logajan sent on Feb 26 (see below) :

In my newbiness ignorance, I'm asking what is the difference between t and
self.x. Aren't they both member of the class C ?

> class C:
>     def __init__(self, b):
>         self.b = b
>         self.x = self.y = 0
>     def Func(self, a):
>         t = a * self.b
>         self.x = t * 2
>         self.y = t + 2




--
Life is not fair
But the root password helps
--

Gregoire Welraeds
greg at perceval.be
Perceval Development team
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On Sat, 26 Feb 2000, James Logajan wrote:

> Date: Sat, 26 Feb 2000 11:16:56 -0800
> From: James Logajan <JamesL at Lugoj.Com>
> To: python-list at python.org
> Newsgroups: comp.lang.python
> Subject: Re: self argument
> 
> Jason Stokes wrote:
> > 
> > london999 at my-deja.com wrote in message <8984mm$5pi$1 at nnrp1.deja.com>...
> > >I am very new to Python, but it appears that every function defined in a
> > >class must have self as a first variable name.
> > 
> > No.  You're just a little confused on a couple of points.  Firstly, member
> > functions always receive the invoked upon class instance as the first
> > argument.  The convention is to call this argument "self", but there's no
> > requirement to do so.  Secondly, not all functions are members of a class.
> > Functions that are not class members don't receive this implicit argument;
> > this way, you can program in conventional functional or procedural style.
> > 
> > > Even better, it would be nice (probably too late
> > >I know), if self was defined implicitly as the "this" pointer is in C++.
> > 
> > I'm not sure why Python's way was chosen, but you get used to it.
> 
> If self were defined implicitly, then you would have to explicitly define
> local variables. This is, today you would do something like:
> 
> class C:
>     def __init__(self, b):
>         self.b = b
>         self.x = self.y = 0
>     def Func(self, a):
>         t = a * self.b
>         self.x = t * 2
>         self.y = t + 2
> 
> If self were implicit, then variables like 't' would need to be declared.
> That leads to some problems. The above might become:
> 
> class C:
>     def __init__(self, b):
>         b = local.b  # Arguments are local.
>     def Func(self, a):
>         local.t = local.a * b
>         x = local.t * 2
>         y = local.t + 2
> 
> Or they could be declared once anywhere in the scope:
> 
> class C:
>     def __init__(self, b): 
>         b = local.b  # Still need to 
>     def Func(self, a):
>         local t = a * b
>         x = t * 2
>         y = t + 2
> 
> 
> I think I like the way the language was designed.
> -- 
> http://www.python.org/mailman/listinfo/python-list
> 
>