Michele Simionato wrote:
> jayessay wrote:
>
>>I was saying that you are mistaken in that pep-0343 could be used to
>>implement dynamically scoped variables. That stands.
>
>
> Proof by counter example:
>
> from __future__ import with_statement
> import threading
>
> special = threading.local()
>
> def getvar(name):
> return getattr(special, name)
>
> def setvar(name, value):
> return setattr(special, name, value)
>
> class dynamically_scoped(object):
> def __init__(self, name, value):
> self.name = name
> self.value = value
> def __context__(self):
> return self
> def __enter__(self):
> self.orig_value = getvar(self.name)
> setvar(self.name, self.value)
> def __exit__(self, Exc, msg, tb):
> setvar(self.name, self.orig_value)
>
> if __name__ == '__main__': # test
> setvar("*x*", 1)
> print getvar("*x*") # => 1
> with dynamically_scoped("*x*", 2):
> print getvar("*x*") # => 2
> print getvar("*x*") # => 1
>
> If you are not happy with this implementation, please clarify.
Can you make it look a little more as if it were part of the language,
or at least conceal the wiring better? I am especially bothered by the
double-quotes and having to use setvar and getvar.
In Common Lisp we would have:
(defvar *x*) ;; makes it special
(setf *x* 1)
(print *x*) ;;-> 1
(let ((*x* 2))
(print *x*)) ;; -> 2
(print *x*) ;; -> 1
kenny
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