Overriding a global

[Chris Angelico]

On Wed, Dec 14, 2011 at 11:05 PM, Jean-Michel Pichavant
<jeanmichel at sequans.com> wrote:
> Chris Angelico wrote:
>>
>> So... it's a bad idea for me to use 'i' many times in my code, with
>> the same name having different meanings in different places? In
>> languages with infinitely-nesting scopes...

> Bad ideas :
>
> i = 5
>
> def spam():
>  for i,v in enumerate([1,2,3,4]):
>   for i,v in enumerate(['a','b', 'c']):
>     print i, v
>   print i,v # bad surprise

That's my point. It's not safe to do it in Python, because the "inner"
local i is the same as the "outer" local i. Python doesn't have block
scope the way most C-like languages do.

int spam()
{
    for (int i=0;i<5;++i)
    {
        for (int i=2;i<4;++i) write("inner "+i+"\n");
        write("outer "+i+"\n");
    }
}

Works perfectly, and the only cost is that variables must be formally declared.

In Python, you can kinda fudge that sort of thing with nested functions.

def spam():
	q=2  # just to prove that the scopes really are nested
	for i in range(5):
		def ham():
			for i in range(2,4):
				print("q = %d, i = %d"%(q,i))
		ham()
		print("i = %d"%i)

It's somewhat clunky, but it does give the illusion of block scope.
Inners mask outers, outers are visible to inner functions. It's an odd
construct though. Very odd.

So... I think I've figured out how to implement from __future__ import braces.

#define { def innerfunc():
#define } innerfunc()

And there you are, out of your difficulty at once!

ChrisA