two quick questions

[Michael Peuser]

Sorry! Correction in case #2 (see below)
Michael

----- Original Message -----
From: "Michael Peuser" <mpeuser at web.de>
Newsgroups: comp.lang.python
Sent: Wednesday, August 13, 2003 9:12 AM
Subject: Re: two quick questions


> The following examples might clear the more rheoretical elaborations .....
>
>
> def noUse(a):
>     a=(4,5,6)
>
> def tricky(a):
>     a[0]=(7,8,9)
>
> # case 1
> x=[1,2,3]
> print x
> tricky(x)
>
> x=(1,2,3)
> # case 2
> noUse(x)  # of course! not: noUse ([x])
> print x
>
> # case 3
> tricky([x])
> print x
>
> # case 4
> y=[x]
> tricky (y)
> print x
> print y[0]
>
> # case 5
> tricky(x)
> print x
>
>
> Kindly
> Michael Peuser
>
> "Erik Max Francis" <max at alcyone.com> schrieb im Newsbeitrag
> news:3F39D89B.A7160172 at alcyone.com...
> > Elaine Jackson wrote:
> >
> > > 1) Does Python have passing-by-reference?
> >
> > It depends on exactly what you mean by that.  In a sense all Python
> > objects are passed by reference, but only in the sense that the
> > reference is passed by value.  (Say that three times fast.)
> >
> > If you want to get the equivalent of a C++ reference on an immutable
> > object, you can do it with containment.  Pass the function a mutable
> > container containing your object, and then manipulate/change the
> > contained object.  In the caller's scope, the container will have
> > mutated.
> >
> > > 2) In ordinary parlance, "deep" implies "shallow" but not conversely.
> > > In the
> > > Python "copy" module (if I understand correctly), the implication goes
> > > the other
> > > way. Do you find this a nuisance?
> >
> > I'm not sure what about the copy's modules semantics you're thinking are
> > reversed, but the terminology used in the copy module is common in
> > computer science.  A shallow copy means that the object is copied, but
> > it will retain the same references to contained objects; a deep copy
> > means that the object is copied, as well as the objects it contains (and
> > so on, recursively).  A deep copy always does the same thing as a
> > shallow copy, and more.
> >
> > --
> >    Erik Max Francis && max at alcyone.com && http://www.alcyone.com/max/
> >  __ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
> > /  \ I always entertain great hopes.
> > \__/  Robert Frost
>
>