A question about reference in Python.

[Chris Rebert]

On Sun, Dec 7, 2008 at 10:09 PM, James Mills
<prologic at shortcircuit.net.au> wrote:
> Hi,
>
> This is really really really pointless code and a really really pointless
> exercise, but nonetheless, here is a very very basic and minimal
> implementation of what you're expecting. This should almost
> *never* be done in Python! Python is a superior dynamic programming
> language, but it's NOT C!
>
> Here goes:
>
> jmills at atomant:~/tmp$ ./list.py
>>>> x[0]
> 0
>>>> x[1]
> 1
>>>> x[2]
> 2
>>>> x[3]
> 3
>>>> x[4]
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
>  File "./list.py", line 36, in __getitem__
>    return node.value
> AttributeError: 'NoneType' object has no attribute 'value'
>>>>
> jmills at atomant:~/tmp$
>
> And the code:
>
> #!/home/jmills/bin/python -i
>
> class Node(object):
>

The following three lines serve no purpose and can only lead to confusion:
>   value = None
>   prev = None
>   next = None
>
>   def __init__(self, value, prev=None, next=None):
>      self.value = value
>      self.prev = prev
>      self.next = next
>
> class List(object):
>
Same with the following line. Why do you have these? Python does *not*
have the concept of instance variable declaration. You are creating
*class variables*, which is almost certainly not what you want.
>   data = None
>

Cheers,
Chris

-- 
Follow the path of the Iguana...
http://rebertia.com

>   def __init__(self, *seq):
>      if seq:
>         first = prev = node = None
>         for x in seq:
>            if not first:
>               first = Node(x)
>               prev = node = first
>            else:
>               node = Node(x, prev)
>               prev.next = node
>               prev = node
>
>         self.data = first
>
>   def __getitem__(self, x):
>      node = self.data
>      for i in xrange(x):
>         node = node.next
>      return node.value
>
> x = List(0, 1, 2, 3)
>
>
> Notes:
>
> I have not implemented any error checking whatsoever.
> I have not implemented any of your normal list
> operations whatsoever (except 1). __getitem__.
>
> Have fun,
>
> cheers
> James
>
> On Mon, Dec 8, 2008 at 3:26 PM, Group <kermit.group at gmail.com> wrote:
>> Hello, I'm studying algorithom. For concentrating on the question itself, I
>> intend to use Python to implement the algorithoms.
>>
>> Now, I want to write a Red-Black Tree, and a List structure. In C/C++, I can
>> use pointers to refer to  children  notes (or next notes). But, in Python,
>> how
>> can I do it? Except the sequence, I know not any way.
>>
>> You'd better help me understan how can I transform the following C code into
>> Python:
>>
>> /* a List */
>> struct {
>>  int data;
>>  int *next;
>>  int *prev;
>> }
>>
>> That's all. Thanks!
>> Kermit
>>
>> --
>> http://mail.python.org/mailman/listinfo/python-list
>>
>
>
>
> --
> --
> -- "Problems are solved by method"
> --
> http://mail.python.org/mailman/listinfo/python-list
>