using "private" parameters as static storage?

[Aaron Brady]

On Nov 13, 11:16 am, Joe Strout <j... 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=[0]):
>       _count[0] += 1
>       return "spam " * _count[0]
>
>  >>> spam()
> 'spam '
>  >>> 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?

Worse yet, if you define a duplicate object at the same scope with the
same name later, it breaks all your references within the function to
itself.

One way around it, which I like the idea of but I'll be honest, I've
never used, is getting a function a 'self' parameter.  You could make
it a dictionary or a blank container object, or just the function
itself.

@self_param
def spam( self ):
      self._count[0] += 1  #<--- how to initialize?
      return "spam " * self._count[0]

Only problem is, how do you initialize _count?

Perhaps 'self_param' can take some initializers, and just initialize
them off of **kwargs in the construction.

@self_param( _count= [] )
def spam( self ):
      self._count[0] += 1
      return "spam " * self._count[0]

Looks really pretty (imo), but untested.