[Changing the subject.]
[Samuele]
> this is a bit OT and too late, but given that our closed over
> variables are read-only, I'm wondering whether, having a 2nd chance,
> using cells and following mutations in the enclosing scopes is
> really worth it, we kind of mimic Scheme and relatives but there
> outer scope variables are also rebindable. Maybe copying semantics
> not using cells for our closures would not be too insane, and people
> would not be burnt by trying things like this:
>
> for msg in msgs:
> def onClick(e):
> print msg
> panel.append(Button(msg,onClick=onClick))
>
> which obviously doesn't do what one could expect today. OTOH as for
> general mutability, using a mutable object (list,...) would allow
> for mutability when one really need it (rarely).
It was done this way because not everybody agreed that closed-over
variables should be read-only, and the current semantics allow us to
make them writable (as in Scheme, I suppose?) if we can agree on a
syntax to declare an "intermediate scope" global.
Maybe "global x in f" would work?
def outer():
x = 1
def intermediate():
x = 2
def inner():
global x in outer
x = 42
inner()
print x # prints 2
intermediate()
print x # prints 42
--Guido van Rossum (home page: http://www.python.org/~guido/)
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