[Tutor] help with refactoring needed -- which approach is
Brian van den Broek
bvande at po-box.mcgill.ca
Thu Feb 10 10:43:02 CET 2005
Alan Gauld said unto the world upon 2005-02-10 02:58:
>>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...
That may well be :-) What I've done is have a class
File_in_the_format, and have all the parsing work going on in methods
of the class. My class is called with a filepath, the __init__ method
calls the _master_parser method which breaks things into head and
body, calling appropriate methods and so on.
I was thinking it was OOP even with just the one class as I am making
use of encapsulation and the class namespace to avoid passing
> 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...
I originally tried to see how to do it that way, but got stuck. I'll
point to where by using your pseudo code below.
> 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() # Stuck here -- BvdB
> if line == NodeEndTag:
> def __del__(self): del self.nodes
I got stuck at the place where I added a comment above. I didn't see
how I could do that, since I didn't yet have all of the node lines in
hand when it would be time to build a node.
> class Node:
> def __init__(self,lines=):
> self.lines = lines
> def append(self,item): # Bing! -- BvdB
> def parse(self):
> # your parsing method here.
Well, that flipped a switch! I *knew in the abstract* that I can
define interfaces [?] like .append and .__add__. The puzzle pieces
just hadn't come together yet. They aren't all there yet either, but a
half an hour in the interpreter has already cleared away much
puzzlement over how to pull this off. So, thanks a lot for the push!
> Whats the advantage? If you have different node types you
> can easily subclass Node and not change the File or Body
> classes, just write a slightl'y different line parser.
> That way your code remains more stable - you never need
> to change working code to add a new node type...
Well, I don't *think* these considerations are going to enter into my
particular task. I'm working with a well documented text format for a
shareware app I have where the developer has recently changed the file
format to an undocumented binary format. So, I can be fairly confident
that my particular target is one I have complete knowledge about.
But, I absolutely see the point for the general case. I'm off to scrap
the code that made me happy :-( and redo it this way to learn better
More information about the Tutor