Deleting objects

[user@domain.invalid]

Say I have an object (foo), that contains an
array (bar) of references to other objects.

Now I want to puff some of the objects from the
array so that I remove the array element, and
destroy the oject.

but when I do:

del foo.bar[0]

Python says:
object doesn't support item deletion

So do I need to define __del__? And what would I
put there?

What if I wanted to remove the array element
but still have the object exist?

What happens if I succeed in destroying an object
that other objects still think they are referencing?

Thanks,

Toby

[Terry Reedy]

Re: Deleting objects


<user@domain.in valid> wrote in message
news:c542f8acd7 55de732c9da8fc3 9fbb50a@news.te ranews.com...[color=blue]
> Say I have an object (foo), that contains an
> array (bar) of references to other objects.
>
> Now I want to puff some of the objects from the
> array so that I remove the array element, and
> destroy the oject.
>
> but when I do:
>
> del foo.bar[0]
>
> Python says:
> object doesn't support item deletion[/color]

What is the actual type of foo.bar? >>>type(foo.bar ) # prints what?

tjr

[Mark McEahern]

Re: Deleting objects

On Wed, 2004-01-14 at 17:23, user@domain.inv alid wrote:[color=blue]
> Say I have an object (foo), that contains an
> array (bar) of references to other objects.
>
> Now I want to puff some of the objects from the
> array so that I remove the array element, and
> destroy the oject.[/color]
[color=blue]
> but when I do:
>
> del foo.bar[0]
>
> Python says:
> object doesn't support item deletion[/color]

It'd be helpful if you supplied the code in question. Then again, we
wouldn't be able to let our imagination wander with what puff might
mean. <wink>

Anyway, is this the sort of thing you're talking about?

#!/usr/bin/env python

class Foo:

def __init__(self):
self.bar = []

def __str__(self):
return '<Foo><bar>%s</bar></Foo>' % (str(self.bar), )

l = range(10)

foo = Foo()
foo.bar.append( l)
del foo.bar[0]
print 'foo = %s' % (str(foo),)
print 'l = %s' % (l,)

Cheers,

// m

[Shalabh Chaturvedi]

Re: Deleting objects

user@domain.inv alid wrote:[color=blue]
> Say I have an object (foo), that contains an
> array (bar) of references to other objects.
>
> Now I want to puff some of the objects from the
> array so that I remove the array element, and
> destroy the oject.[/color]

You don't need to jump through hoops for this. All you need to do is:

del foo

If there are no other references to the object that was called foo
above, then (and only then) it will be destroyed.

Python keeps a reference count for each object. When the count hits 0
(no references pointing to object) it is destroyed.

Because of this, attributes of foo (eg foo.bar) will automatically be
destroyed when foo is destroyed (assuming they don't have references
from elsewhere).
[color=blue]
>
> but when I do:
>
> del foo.bar[0]
>
> Python says:
> object doesn't support item deletion
>
> So do I need to define __del__? And what would I
> put there?[/color]

What is the type of foo.bar?
[color=blue]
>
> What if I wanted to remove the array element
> but still have the object exist?[/color]

del foo.bar

This will remove the reference foo.bar.
[color=blue]
> What happens if I succeed in destroying an object
> that other objects still think they are referencing?[/color]

Try as you might, shooting yourself in the foot is pretty hard in Python
(see above :)

--
Shalabh