Static Variables

[Andrew Dalke]

Jim Jacobs:
>Is it possible to simulate "C" style static variables in functions?  In
>methods?

Depends on which aspect you're looking for.  You probably want
something like:

_cache = {}
def spam(i):
  if i in _cache:
    return _cache[i]
  x = hairy_algorithm_with_big_pointy_teeth(i)
  _cache[i] = x
  return x

Notes on the differences:
  '_cache = {}' is executed once, but during module import.  In C,
all statics are initialized before main is called (or is that C++?).

  'static' is used in C functions as a way to hide scope.  That's
less needed in Python because module variable have module scope, while
C variables have "compilation unit" scope.

  If you wanted to change the actual value of '_cache' (that is,
replace it with a different reference) you would need to declare it
in the function as 'global'.

  Variables starting with an '_' are not imported during "import *"

  If you want more complicated functions, you can also create a
function object, like

class spam:
  def __init__(self):
    self._cache = {}
    # prefill the cache
    for i in range(10):
      self(i)
  def __call__(self, i):
    if i in self._cache:
      return _cache[i]
    x = hairy_algorithm_with_big_pointy_teeth(i)
    _cache[i] = x
    return x

spam = spam()

'static' does other things than this; is there something else you
are looking for?

                    Andrew
                    dalke at dalkescientific.com