classes for fun and newbies

[Bruce Dykes]

----- Original Message -----
From: "Max M" <maxm at mxm.dk>
Newsgroups: comp.lang.python
To: <python-list at python.org>
Sent: Wednesday, March 20, 2002 09:30
Subject: Re: classes for fun and newbies


> It would probably be simpler to it with just a function in this case:
>
> id   = (0,5)
> date = (6,11)
>
> def getPart(slice, line):
>      return line(slice[0]:slice[1])
>
> print getPart(id, log[1])
>
> or something like that. But just writing it in one big mess is probably
> not out of the question either.
>
> for line in,lines:
>      id, date = line[0:5], line[6:11]
>
> But then you could do something like (untested).
>
> class Rec:
>
>      def __init__(self, line):
>          self.line = line
>
>      def __getattr__(self, attr):
>          if attr == 'id':
>              return self.line[0:5]
>          if attr == 'date':
>              return self.line[6:11]
>
> class Log:
>
>      def __init__(self, fileName):
>          f = open(fileName,'r')
>          self.lines = f.readlines()
>          f.close()
>
>      def __getitem__(self, index):
>          return Rec(self.lines[index])
>
>      def __len__(self):
>          return len(self.lines)
>
> Then you can use it like:
>
> log = Log('logfile.log')
> print log[1].id
>
> or like:
>
> for item in log:
>      print item.id
>
> regards Max M

Now, none of these seem as obvious-to-write or as readable-at-a-later-date
as setting each record up as a class first. And setting up the class at the
start seems to be almost self documenting (heck, I *generated* the class
definition from the documentation 8-).

Is there any particular reason to prefer using functions over class
definitions, such as performance, or memory use? Or are we just speaking of
stylistic differences?

> Generally there is no need ti write objects before it is needed. Ie.
> when your code violates the DRY (Dont Repeat Yourself) principle.

As I said, it just seems more natural to me to define each record/line as an
object, with each field being an attribute.

aside: I realize that I'm actually building the guts of a database, but for
something this small, it seems far more efficient to simply write the
necessary text processing and search functions than to build a database in
MySQL or PostgreSQL and then build the necessary connections and filters. A
couple of Python scripts *must* be more lightweight than a fullbore
database.

bkd