[Tutor] help with refactoring needed -- which approach is morePythonic?

Kent Johnson kent37 at tds.net
Thu Feb 10 11:52:51 CET 2005

Alan Gauld wrote:
>>The main change in refactoring is moving it to OOP. I have a method
>>that serves as the entry point for parsing the files.
> Not an object? If you are thinking terms of what the methods
> do its probably not OOP...
> I would expect to see an object for the File, another for the Header,
> a third for the Body and another for the Node. The first (containing
> a header and bosdy object) is responsible for cracking open the file
> and reading the lines, recognising where it has a header and sending
> those lines to the header object and the rest to the bosy object.
> The body object then reades those lines and creates a Node object
> per node feeding it lines as appropriate...

This is a reasonable approach. Having the Body and Node classes gives a handy place to put functions 
to do something with that data. But I tend to take the Extreme Programming position of You Aren't 
Going To Need It. I would probably stick with the list representation of Node, for example, until I 
had some real work for the Node class to do.

It's definitely a judgement call when to introduce classes, there isn't a right way and a wrong way. 
Some problems cry out for classes, some clearly have no need, and then there is a gray area in the 

> Pseudo code:
>        class Body:
>           def __init__(self,content):
>             self.contents = contents
>             self.nodes = []
>           def parse(self):
>              for line in self.contents:
>                  if line == NodeStartTag:
>                     node = Node()
>                  if line == NodeEndTag:
>                     self.nodes.append(node)
>                  node.append(line)
>           def __del__(self): del self.nodes

Why is 'del self.nodes' needed? When the Body is del'ed the reference to self.nodes should be lost 
and the nodes list will be GC'd. Or am I missing something?

>        class Node:
>          def __init__(self,lines=[]):
>               self.lines = lines
>          def append(self,item):
>               self.lines.append(item)
>          def parse(self):
>               # your parsing method here.

You might want to extend list so a Node automatically has the behavior of a list.


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