using "private" parameters as static storage?

rurpy at yahoo.com rurpy at yahoo.com
Thu Nov 13 19:58:49 CET 2008


On Nov 13, 11:32 am, "J. Cliff Dyer" <j... at sdf.lonestar.org> wrote:
> On Thu, 2008-11-13 at 09:38 -0800, Matimus wrote:
> > On Nov 13, 9:16 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 '
>
> > Don't Do this, it is confusing and there are definitely (many) better
> > facilities in python for handling saved state.
>
> > > 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 is definitely preferred over the first. However the preferred
> > method is just to use a class. Preserving state is what classes are
> > for.
>
> Preserving state is what *objects* are for.

Not exclusively, generators also preserve state.

def _spam():
  count = 1
  while 1:
      yield "spam " * count
      count += 1
spam = _spam.next()




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