call by reference howto????

[castironpi at gmail.com]

On Feb 29, 8:12 am, Steve Holden <st... at holdenweb.com> wrote:
> castiro... at gmail.com wrote:
> > On Feb 29, 5:56 am, Steve Holden <st... at holdenweb.com> wrote:
> >> castiro... at gmail.com wrote:
> >>> On Feb 27, 6:02 pm, Tamer Higazi <n... at mail.de> wrote:
> >>>> Hi!
> >>>> Can somebody of you make me a sample how to define a function based on
> >>>> "call by reference" ???
> >>>> I am a python newbie and I am not getting smart how to define functions,
> >>>> that should modify the variable I passed by reference.
> >>>> thanks in advance
> >>>> Tamer
> >>> If it's a mutable object, avoid the pitfalls of rebinding the
> >>> parameter, and just modify the object.
> >>> BAD:
> >>> def f( a ):
> >>>    a= { 'this': 'that' }
> >>> GOOD:
> >>> def f( a ):
> >>>    a.clear()
> >>>    a[ 'this' ]= 'that'
> >> BETTER:
>
> >> class Thang: pass
>
> >> def f(a):
> >>      a.this = "that"
>
> >> thang = Thang()
> >> f(thang)
>
> [please refrain from quoting signatures in your replies]
> [better still, use a mailer that omits them from the quote!]
>
> >> - Show quoted text -
>
> > What does __coerce__ look like, so you could operate on a.this without
> > accessing 'this' member every time?  For numbers maybe, but what about
> > __getattr__( self, name ): return getattr( self.this, name ) for
> > strings?  Then thang.this= "that"; thang.find( 'at' ) ->
> > thang.this.find( 'at' ).  Awesome!
>
> Where did __coerce__ come from? Stick with the main party, please.
>
> __coerce__ is an old mechanism intended to be used to bring numeric
> types into alignment, and AFAICS has nothing at all to do with whatever
> idea you are suggesting.
>
> As near as I can make out you appear to want to have thang delegate
> certain of its method to thang.this. The easiest way to do that would be
> to implement a __getattr__() in the Thang class to do so, but remember
> that it won't be called for cases where the class has a real attribute
> with the correct name.

In your example,

> class Thang: pass
>
> def f(a):
>      a.this = "that"
>
> thang = Thang()
> f(thang)

Thang -wasn't- doing anything else.  It can delegate everything.
(Thang& operator=( const Thang& );.)  Then there's __getattribute__,
which is called unconditionally, just in case you implement something
in Thang besides 'this' on accident.