Why self?

[Daniel Fackrell]

"Charles Hixson" <charleshixsn at earthlink.net> wrote in message
news:agfb5204pg at enews3.newsguy.com...
> Alex Martelli wrote:
> > Robb Shecter wrote:
> >
> >
> >>Brian Quinlan wrote:
> >>
> >>>...  Actually, private instance
> >>>variables are uncommon in general.
> >>
> >>Sounds like a difference in design philosophies.  In my code, private
> >>everything is the norm, with a very thin/small public API.
> ...
> > Alex
> >
>
> If you are subclassing a class that someone else has written, you don't
> want to accidentally redefine an internal name.  Sorry.  I can accept
> that you should be able to explicitly access it, but to be able to
> change it by accident is (would be?) a misfeature.
>
> I didn't believe that this happened in Python.  It does, and it seems a
> significant flaw.  My understanding is that if you define a variable in
> a class that subclasses another class, then unless you take definite
> steps to cause things to happen otherwise, you are defining a new
> variable that is local to the scope of the class that you are currently
> defining, and will not impact routines that you call from parental
> classes.  Experiment shows that this isn't what happens.
> from __future__ import nested_scopes
> does not fix this problem, as I assumed that it would.
>
> Let's be explict:
> from __future__ import nested_scopes
> class A:
>     def ma(self):
>         print  "ma, ma"
>     def pa(self):
>         self.ma()
> class B(A):
>     def ma():
>         print "hello, world"
> tst = B()
> tst.pa()
>
> Testing this produces the message, "hello, world"
> This seems to be the wrong message.  The version of pa that was called
> was the version defined in class A, so the routine called should have
> been the routine defined in class A.
>
> Or, to me more accurate, for libraries to have maximal portability, I
> would want the message to have generated "ma, ma", and I had been
> assuming that nested_scopes would result in that being the message that
> was produced.
> --
> -- Charles Hixson
> Gnu software that is free,
> The best is yet to be.

You can get the behavior you wanted by defining A as:

class A:
    def ma(self):
        print "ma, ma"
    pa=ma

--
Daniel Fackrell (dfackrell at linuxmail.org)
When we attempt the impossible, we can experience true growth.