static variables in Python?

John Machin sjmachin at lexicon.net
Wed Jul 30 04:16:39 CEST 2008


On Jul 30, 11:57 am, "Russ P." <Russ.Paie... at gmail.com> wrote:
> On Jul 29, 6:33 pm, "Russ P." <Russ.Paie... at gmail.com> wrote:
>
>
>
> > On Jul 29, 1:40 pm, kj <so... at 987jk.com.invalid> wrote:
>
> > > Yet another noob question...
>
> > > Is there a way to mimic C's static variables in Python?  Or something
> > > like it?  The idea is to equip a given function with a set of
> > > constants that belong only to it, so as not to clutter the global
> > > namespace with variables that are not needed elsewhere.
>
> > > For example, in Perl one can define a function foo like this
>
> > > *foo = do {
> > >   my $x = expensive_call();
> > >   sub {
> > >     return do_stuff_with( $x, @_ );
> > >   }
>
> > > };
>
> > > In this case, foo is defined by assigning to it a closure that has
> > > an associated variable, $x, in its scope.
>
> > > Is there an equivalent in Python?
>
> > > Thanks!
>
> > > kynn
> > > --
> > > NOTE: In my address everything before the first period is backwards;
> > > and the last period, and everything after it, should be discarded.
>
> > If the constant parameters are really only needed in one particular
> > function, you can use default function arguments. An added benefit is
> > that you can override them with another value if necessary.
>
> > def fun(x, y, parameter1=0, parameter2=1):
> >     ...
>
> I should add that the parameters need not be literal numbers. They can
> be computed values as well. They will be computed only once, on the
> first pass through the function definition, which I presume is exactly
> what you want.
>
> I think this is the simplest solution to the problem you posed.

Here's a real-life example, where the second and third args are run-
time constants:

def unescape(s,
    subber=re.compile(r'_x[0-9A-Fa-f]{4,4}_').sub,
    repl=lambda mobj: unichr(int(mobj.group(0)[2:6], 16)),
    ):
    if "_" in s:
        return subber(repl, s)
    return s
# The if test is just an optimisation that unfortunately the re module
doesn't nut out for itself.

Cheers,
John



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