[Tutor] Defining a new class

[D-Man]

On Mon, Mar 19, 2001 at 10:35:42PM -0700, VanL wrote:
| Hello,
| 
| I am just getting started with Python so I thought I would implement
| a lot of the classical data structures in Python so as to get a feel
| for it.  I am running into a few difficulties, tho.  Here is my
| first Python class:
| 
| class LinkedList:
| 
|     def __init__(self, name, object=None):
|         self.label = name
|         if object: self.link = object
|         else: self.link = None

I just want to ask why you check the value of 'object' here?  If the
client doesn't give a value for object it will be None, which is what
you set it to in the else clause.  I think that the following will be
semantically equivalent to what you want:

     def __init__( self , name , object=None ) :
        self.label = name
        self.link = object

| 
|     def next(self):
|         if self.link: return link
|         else: return None

same here.  self.link will already be None, so why return None
explictly?  Another consideration :  if you provide a function such as
is_last() or has_next() that will indicate whether or not there is
another node in the list, this function can throw an exception when
there is nothing left in the list.

I don't think perl has exceptions, so your Perl book probably uses a
C-like setinel return value to indicate an error (null , None , etc).
Python has exceptions which make error handling much nicer and easier.

(if you want some more info/examles using exception just holler, or
check the archives of this and python-list for messages from me (they
center around raw_input and converting to a number))

|     def label(self):
|         return self.label
| 
|     def link(self, object):
|         self.link = object
| 
|     def unlink(self):
|         self.link = None
| 
|     def rename(self, name):
|         self.label = name
| 
| 
| Some things work as expected; I can declare an object of type
| LinkedList.  I get some strange results overall, tho.  For example:

I'll assume you have already corrected these from everyone else's
responses ;-).

| Thanks very much,
| 
| Van