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...
Hi Alan,
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
parameters about.
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.
<SNIP>
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:
self.nodes.append(node)
node.append(line)
def __del__(self): del self.nodes
<SNIP>
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
self.lines.append(item)
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
habits :-)
Thanks again,
Brian vdB
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