Newbie question about nested lists and constructor functions...

[Chris Gonnerman]

----- Original Message -----
From: "Norm Lyons" <norm at cybersurf.net>
Sent: Sunday, March 04, 2001 10:18 PM
Subject: Re: Newbie question about nested lists and constructor functions...


> Sorry about that Chris.

S'awright.

> I am trying to create instantiated objects with the following properties:
>
> list_var = [(key, value), left, right]
>
> where the "key, value" pair are a tuple, and the variables "left" and
> "right" are empty lists [ ] which will be manipulated to hold values later
> in the program after they have already been initialized to empty lists.
The
> purpose of this object is to hold the necessary data for nodes in a binary
> search tree.  I know how to implement this type of data structure in C++
but
> I seem to be getting hung up on the syntax differences in the Python class
> and member variable declarations.
>
> An example of one of my attempts would be:
>
> class Node:
>      def __init__(self, key = ''):
>           left = []
>           right = []
>           data = (key, 'value')
>           newnode = [data, left, right]
>      def info(self):
>           return self.data

OKAY.  Now we are getting somewhere.  This seems to be a common mistake for
users of other languages.  Your code likely should be like this:

class Node:
     def __init__(self, key = ''):
          left = []
          right = []
          data = (key, 'value')
          self.data = [data, left, right]
     def info(self):
          return self.data[0]

SPECIFICALLY, you need to assign your list to a data attribute of self.  I
would write
your code more like this:

class Node:
     def __init__(self, key = ''):
          self.left = []
          self.right = []
          self.data = (key, 'value')
     def info(self):  # not really needed with this version IMHO
          return self.data

or perhaps:

class Node:
     def __init__(self, key = '', value = ''):
          self.left = None   # these get object references (later)
          self.right = None  # so I don't think they need to be lists.
          self.key = key
          self.value = value  # is this a default?
     def info(self):  # not really needed with this version IMHO
          return (self.key, self.value)

but that is a personal thing.

> The "info" function is only intended to return the values of the variables
> "key and value".  The other values are used as pointers to child nodes in
> the tree.  As I mentioned earlier, I have been through the online tutorial
a
> few times and have not found any information that clears this issue up for
> me.  Obviously, the code above is incomplete as it should also contain the
> appropriate "if" and "elif" statements to properly branch according to the
> information passed to the constructor function.  Unfortunately, I do not
> know what I am doing wrong.  Any suggestions?

I think I have this all right, but I haven't test run it yet.  Good luck :-)