[Python-Dev] PEP 342: simple example, closure alternative

[Alain Poirier]

Le Vendredi 26 Août 2005 16:57, Guido van Rossum a écrit :
> On 8/25/05, Ian Bicking <ianb at colorstudy.com> wrote:
> > More generally, I've been doing some language comparisons, and I don't
> > like literal but non-idiomatic translations of programming patterns.
>
> True. (But that doesn't mean I think using generators for this example
> is great either.)
>
> > So I'm considering better ways to translate some of the same use cases.
>
> Remember that this particuar example was invented to show the
> superiority of Lisp; it has no practical value when taken literally.
> If you substitute a method call for the "acc += incr" operation, the
> Python translation using nested functions is very natural. For larger
> examples, I'd recommend defining a class as always.

For example, I often use this class to help me in functional programming :

  _marker = ()

  class var:
      def __init__(self, v=None):
          self.v = v

      def __call__(self, v=_marker):
          if v is not _marker:
              self.v = v

          return self.v

and so the nested functions become very functional :

  def accum(n):
      acc = var(n)
      return lambda incr: acc(acc()+incr)