[Tutor] Re: Help with classes

[Bob Gailer]

At 12:22 PM 4/7/2005, Andrei wrote:
>Kevin <python.programming <at> gmail.com> writes:
>
> > I am fooling around with classes and I was trying to create a very
> > small one player text adventure. I made a class called commands here
> > it is:
> > class Commands:
> >     def __init__(self):
> >         pass
> >     def quiting(self):
> >         sys.exit()
><snip>
> > I want to beable to type in a command from the list at the prompt and
> > have it call one of the functions from the class. I was looking for a
> > shorter way to write it but the only way I can think of is with an if
> > statment for each command. Is there a better way or shorter way to do
> > this?
>
>I don't think you're making proper use of classes.

IMHO there is no "proper use of classes".

>A class is a collection of data and methods related to that data.

In Python a class is whatever one creates using the class statement. In 
teaching OOP we often use "collection of data and methods related to that 
data" to help learners appreciate the application of classes. But I'd not 
want to limit classes to that explanation.

Understanding the mechanism behind Python classes opens many doors to many 
uses of classes.

Kent's proposal makes IMHO excellent use of the class mechanism. One may 
also access the class __dict__ directly in lieu of using getattr.

>The Commands class is merely a collection of unrelated methods.

But they are related. Each represents a game command; the class is the 
container for the commands. And it might be that as the program expands 
that there would be multiple instances representing players or saved games 
or ??? And class properties would keep track of the player's status.

>MO the natural solution for your problem would be a
>dictionary, where a command is mapped to a function. You'd ask the player 
>for a
>command, strip + lowercase it and check if you have a key of that name in your
>commands dictionary and if that is the case, run the associated function. 
>It's a
>shorter solution and easier to maintain than making a class, keeping a list of
>commands and inspecting a Commands object to see if something is available.
>
>Possible classes in a text adventure could be a Player class (which could
>contain a list of items which the Player carries, life points, etc.), a Room
>class (which could contain information and methods related to the room the
>player is in plus the connected rooms), an Item class (with subclasses for
>different types of items, where different implementations of e.g. PickUp 
>methods
>would determine if the player could pick up a pencil or a skyscraper), etc.
>
>Yours,
>
>Andrei
>
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Bob Gailer
mailto:bgailer at alum.rpi.edu
510 558 3275 home
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