using "private" parameters as static storage?
arkanes at gmail.com
Thu Nov 13 18:19:30 CET 2008
On Thu, Nov 13, 2008 at 11:16 AM, Joe Strout <joe at strout.net> wrote:
> One thing I miss as I move from REALbasic to Python is the ability to have
> static storage within a method -- i.e. storage that is persistent between
> calls, but not visible outside the method. I frequently use this for such
> things as caching, or for keeping track of how many objects a factory
> function has created, and so on.
> Today it occurred to me to use a mutable object as the default value of a
> parameter. A simple example:
> def spam(_count=):
> _count += 1
> return "spam " * _count
> 'spam '
> 'spam spam '
> This appears to work fine, but it feels a little unclean, having stuff in
> the method signature that is only meant for internal use. Naming the
> parameter with an underscore "_count" makes me feel a little better about
> it. But then, adding something to the module namespace just for use by one
> function seems unclean too.
> What are your opinions on this idiom? Is there another solution people
> generally prefer?
> Ooh, for a change I had another thought BEFORE hitting Send rather than
> after. Here's another trick:
> def spam2():
> if not hasattr(spam2,'count'):spam2.count=0
> spam2.count += 1
> return "spam2 " * spam2.count
> This doesn't expose any uncleanliness outside the function at all. The
> drawback is that the name of the function has to appear several times within
> itself, so if I rename the function, I have to remember to change those
> references too. But then, if I renamed a function, I'd have to change all
> the callers anyway. So maybe this is better. What do y'all think?
Static storage is a way of preserving state. Objects are a way of
encapsulating state and behavior. Use an object.
More information about the Python-list