list insertion

[Randy Bush]

i am trying to insert into a singly linked list

hold = self.next
self.next = DaClass(value)
self.next.next = hold

but i suspect (from print statement insertions) that the result
is not as i expect. as the concept and code should be very
common, as i am too old for pride, i thought i would ask.

mahalo,
randy

[Jordan Rastrick]

Re: list insertion

What you've posted looks right, more or less.

To get any sort of meaningful feedback, you really need to post a full
version of your code, including the print statements, what's being
printed, and why you think this shows the code is not working. What
you've shown is far too little for anybody else to work with.

Regards,
Jordan


Randy Bush:[color=blue]
> i am trying to insert into a singly linked list
>
> hold = self.next
> self.next = DaClass(value)
> self.next.next = hold
>
> but i suspect (from print statement insertions) that the result
> is not as i expect. as the concept and code should be very
> common, as i am too old for pride, i thought i would ask.
>
> mahalo,
> randy[/color]

[Sybren Stuvel]

Re: list insertion

Randy Bush enlightened us with:[color=blue]
> hold = self.next
> self.next = DaClass(value)
> self.next.next = hold[/color]

shouldn't that last line be this?
self.next.prev = hold
[color=blue]
> but i suspect (from print statement insertions) that the result is
> not as i expect.[/color]

What did you expect, and what did you ovserve?

Sybren
--
The problem with the world is stupidity. Not saying there should be a
capital punishment for stupidity, but why don't we just take the
safety labels off of everything and let the problem solve itself?
Frank Zappa

[Ross Wilson]

Re: list insertion

On Tue, 23 Aug 2005 20:58:11 -0700, Randy Bush wrote:
[color=blue]
> i am trying to insert into a singly linked list
>
> hold = self.next
> self.next = DaClass(value)
> self.next.next = hold
>
> but i suspect (from print statement insertions) that the result
> is not as i expect. as the concept and code should be very
> common, as i am too old for pride, i thought i would ask.
>
> mahalo,
> randy[/color]

The example above looks like it would work, as long as other
stuff you _don't_ show is fine. Specifically, how do you
handle the case when the list is empty?

Better to show a more complete example with output and how that
is not what you expect.

Ross

[Randy Bush]

Re: list insertion

>> hold = self.next[color=blue][color=green]
>> self.next = DaClass(value)
>> self.next.next = hold[/color]
> shouldn't that last line be this?
> self.next.prev = hold[/color]

single threaded list
[color=blue]
> What did you expect, and what did you ovserve?[/color]

i will try to distill a case

randy

[Bengt Richter]

Re: list insertion

On Tue, 23 Aug 2005 20:58:11 -0700, Randy Bush <randy@psg.co m> wrote:
[color=blue]
>i am trying to insert into a singly linked list
>
> hold = self.next
> self.next = DaClass(value)
> self.next.next = hold
>
>but i suspect (from print statement insertions) that the result
>is not as i expect. as the concept and code should be very
>common, as i am too old for pride, i thought i would ask.
>[/color]
I think you're fine. Here's some possible context for your code:
[color=blue][color=green][color=darkred]
>>> class DaClass(object) :[/color][/color][/color]
... def __init__(self, value):
... self.value = value
... self.next = None
... def values(self):
... while True:
... yield self.value
... if self.next is None: break
... self = self.next
... def insert(self, value):
... hold = self.next
... self.next = DaClass(value)
... self.next.next = hold
... return self
... def __repr__(self):
... return '<DaClass %s>'%(' -> '.join(map(repr , self.values())) )
...
...[color=blue][color=green][color=darkred]
>>> sll = DaClass(1)
>>> sll[/color][/color][/color]
<DaClass 1>[color=blue][color=green][color=darkred]
>>> sll.insert(2)[/color][/color][/color]
<DaClass 1 -> 2>[color=blue][color=green][color=darkred]
>>> sll[/color][/color][/color]
<DaClass 1 -> 2>[color=blue][color=green][color=darkred]
>>> sll.insert('a')[/color][/color][/color]
<DaClass 1 -> 'a' -> 2>[color=blue][color=green][color=darkred]
>>> sll.next[/color][/color][/color]
<DaClass 'a' -> 2>[color=blue][color=green][color=darkred]
>>> sll.next.insert ('b')[/color][/color][/color]
<DaClass 'a' -> 'b' -> 2>[color=blue][color=green][color=darkred]
>>> sll[/color][/color][/color]
<DaClass 1 -> 'a' -> 'b' -> 2>

Regards,
Bengt Richter

[Randy Bush]

Re: list insertion

>> hold = self.next[color=blue][color=green]
>> self.next = DaClass(value)
>> self.next.next = hold
>>
>> but i suspect (from print statement insertions) that the result
>> is not as i expect. as the concept and code should be very
>> common, as i am too old for pride, i thought i would ask.[/color]
> I think you're fine.[/color]

indeed. the bug was elsewhere. i got confused and tried to
look-ahead too far when i could have just recursed. i threw
away the too-clever code and replaced it with one line. i
love it when that happens.

randy