Factories in Python

Re: Factories in Python

Robert Ferrell wrote:

[snip][color=blue]
>
> However, I'm guessing that I'm not understanding other benefits of
> using factories in Python. Does anybody have examples or pointers
> on how use of factories in Python?[/color]

Here is a link:



A reason for using a factory is that the client (the code that
creates the instance) does not know which class or sub-class it
wants to create an instance of. So, you build a factory that is
smart enough to create an instance of the right class.

In my case, while parsing an XML document and creating instances
of nodes in the tree that represents the document, the classes
(the super-class of each node class) does the parsing. However,
each super-class must be smart enough to create a tree populated
with instances of sub-classes, which may contain additional custom
code,*if* they are available.

I'd be interested in other reasons for using factories.

- Dave

--
Dave Kuhlman

[email protected] om

Re: Factories in Python

Dave Kuhlman wrote:[color=blue]
> I'd be interested in other reasons for using factories.[/color]

My most frequent reason for using factories is to insulate client code from
refering directly to a class name. I find I do this most often when I have
code that's likely to change soon or change frequently. This approach
allows me to leave client code unchanged although the actual class names
and implementations may vary greatly.

Consider:

class MightBeWhatIWan t:
pass

class HelperForThat:
pass

def build():
return MightBeWhatIWan t()

As the problem is revealed thru elbow grease, this might change:

class ThisIsWhatIReal lyNeeded:
pass

class SomethingIMisse dEarlier:
pass

def build():
return ThisIsWhatIReal lyNeeded()

Granted, these aren't factories in the strictest GoF sense, but I think the
intent is clear.

troy