block scope?

[Alex Martelli]

Neal Becker <ndbecker2 at gmail.com> wrote:
   ...
> > i = 5
> > for my i in xrange(4):
> >    if i:             # skips first when i is 0
> >      my i = 100
> >      if i:
> >        print i       # of course 100
> >      break
> >    print i           # i is between 0 & 3 here
> > print i             # i is 5 here
> > 
> > 
> > Doesn't leave a particularly bad taste in one's mouth, I guess (except
> > for the intended abuse).
> > 
> > James
> 
> Yes, the above is pretty much what I had in mind.  +1.

I prefer Java's approach (14.4.2 in the JLS 2nd edition): forbid "inner"
blocks from shadowing variables in "outer" ones.  I quote:
"""
If a declaration of an identifier as a local variable of the same
method, constructor, or initializer block appears within the scope of a
parameter or local variable of the same name, a compile-time error
occurs.
Thus the following example does not compile:

class Test {
        public static void main(String[] args) {
                int i;
                for (int i = 0; i < 10; i++)
                        System.out.println(i);
        }
}
This restriction helps to detect some otherwise very obscure bugs.
"""
I entirely agree with the JLS here, having fought just such bugs in C++
and other languages that lack the restriction in question.  I just wish
Python had adopted the same restriction regarding nested functions, when
proper lexical scoping was introduced -- I argued for it at the time,
but backwards compatibility blocked its introduction.  There are
definitely NOT many Java-specific language characteristics that I like,
but this one is a winner!-)  [[but, I disagree with the lack in Java of
a similar restriction against shadowing between instance variables and
local variables, and the weak rationale for that in the JLS:-)]].


Alex