[Zope] Python script: problem with session

[Chris McDonough]

The copy method of a dictionary returns a "shallow" copy of the
dictionary.  If you are changing elements of the dictionary that are
themselves mutable, you will still have problems.  Here are the
rules (from the Python docs):

The difference between shallow and deep copying is only relevant for
compound objects (objects that contain other objects, like lists or
class instances):

  a.. A shallow copy constructs a new compound object and then (to
the extent possible) inserts references into it to the objects found
in the original.

  b.. A deep copy constructs a new compound object and then,
recursively, inserts copies into it of the objects found in the
original.
Providing you with more information would require that we know all
the items in the 'foo' dictionary.  If any of them is mutable, and
you're changing it, you would see the behavior you describe.

----- Original Message -----
From: "p.t." <p.training@tin.it>
To: "Chris McDonough" <chrism@zope.com>
Sent: Wednesday, June 12, 2002 12:17 PM
Subject: Re: [Zope] Python script: problem with session


> Sorry, Chris, you are right.
> "not working" means that the assignment is Ok, but the chamges are
still
> reflected on the referenced item.
>          p.t.
>
> At 10:38 12/06/2002 -0400, you wrote:
> >When you say "not working" what does that mean?  What do you go
on
> >to do that doesn't work?
> >----- Original Message -----
> >From: "p.t." <p.training@tin.it>
> >To: "Chris McDonough" <chrism@ZOPE.COM>
> >Cc: <zope@zope.org>
> >Sent: Wednesday, June 12, 2002 10:19 AM
> >Subject: Re: [Zope] Python script: problem with session
> >
> >
> > > Fine, Chris.
> > > I'll try your suggestion exactley in the way you wraite it
down.
> > > I've already tryied this:
> > >
> > > context.REQUEST['foo'] = context.REQUEST.SESSION['foo'].copy()
> > >
> > > but (suprisingly) not working (and no error issue).
> > > Things work fine "renaming" objects, like:
> > >
> > > Initialise:
> > > context.REQUEST.SESSION['FOO'] = foo
> > >
> > > Assign:
> > > context.REQUEST['foo'] = context.REQUEST.SESSION['FOO']
> > >
> > > but this is quite impratical, because I'm often using indirect
> >naming via
> > > the Zope function getitem().
> > > Thanks,
> > >          p.t.
> > >
> > > At 10:01 12/06/2002 -0400, Chris McDonough wrote:
> > > >I see... when you hold a reference to a dictionary in two
places
> >you
> > > >are holding a reference to the same object, therefore changes
> >made
> > > >via one reference are reflected when you take a look at the
> >object
> > > >via the other reference.
> > > >
> > > >One way to avoid this in your case in a Python Script:
> > > >
> > > >d = context.REQUEST.SESSION['foo']
> > > >REQUEST['foo'] = d.copy()
> > > >
> > > >In other words, don't assign the value of SESSION['foo'] to
> > > >REQUEST['foo'], rather assign a copy.
> > > >
> > > >----- Original Message -----
> > > >From: "p.t." <p.training@tin.it>
> > > >To: "Chris McDonough" <chrism@zope.com>
> > > >Cc: <zope@zope.org>
> > > >Sent: Wednesday, June 12, 2002 9:41 AM
> > > >Subject: Re: [Zope] Python script: problem with session
> > > >
> > > >
> > > > > Chris,
> > > > > it is a mapped object (a dictionary).
> > > > > A closer view is:
> > > > >
> > > > > First (in a calling procedure) I put in
> > > > > SESSION[processID]['status']['dataTable'] the name of a
table.
> > > > > Then (in the called procedure) I retrieve this name to the
> >current
> > > >status:
> > > > > REQUEST['status'] = SESSION[processID]['status']
> > > > >
> > > > > REQUEST['status'] can change some values before calling
back
> >the
> > > >caller.
> > > > > TIA,
> > > > >          p.t.
> > > > >
> > > > > At 09:10 12/06/2002 -0400, Chris McDonough wrote:
> > > > > >What kind of object does REQUEST['foo'] return?
> > > > > >
> > > > > >On Wed, 2002-06-12 at 08:43, p.t. wrote:
> > > > > > > I did already post this with a different thread:
probably
> >the
> > > >formulation
> > > > > > > was to complex. Or may be there is some very basic
> >knowledge
> > > >I'm missing.
> > > > > > > I'll try again.
> > > > > > >
> > > > > > > If I assign to variable in a Python script (say
> > > >context.REQUEST['foo']) a
> > > > > > > value stored in SESSION (say context.SESSION['foo']),
and
> >then
> > > >I change
> > > > > > the
> > > > > > > retrieved value (the one in REQUEST, not the original
> >one),
> > > >also the
> > > > > > > variable in SESSION is changed. In this way I have
lost my
> > > >original
> > > > > > > information stored in SESSION!
> > > > > > >
> > > > > > > I've tryied to avoid this, but I can't manage to find
how.
> > > > > > > Any suggestion?
> > > > > > >
> > > > > > > TIA,
> > > > > > >       p.t.
> > > > > > >
> > > > > > >
> > > > > > >
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