[Python-Dev] accumulator display syntax

[Michael Hudson]

Greg Ewing <greg at cosc.canterbury.ac.nz> writes:

> Michael Hudson <mwh at python.net>:
>
>> In particular what happens if the iteration variable is a local in the
>> frame anyway?  I presume that would inhibit the renaming
>
> Why?

Well, because then you have the same name for two different bindings.

>> but then code like 
>> 
>> def f(x):
>>     r = [x+1 for x in range(x)]
>>     return r, x
>> 
>> becomes even more incomprehensible (and changes in behaviour).
>
> Anyone who writes code like that *deserves* to have the
> behaviour changed on them!

This was not my impression of the Python way.  I know I'd be pretty
pissed if this broke my app.

I have no objection to breaking the above code, just to breaking it
silently!  Having code *silently change in behaviour* (not die with an
expection, post a warning at compile time or fail to compile at all)
is about an evil a change as it's possible to contemplate, IMO.

> If this is really a worry, an alternative would be to
> simply forbid using a name for the loop variable that's
> used for anything else outside the loop. That could
> break existing code too, but at least it would break
> it in a very obvious way by making it fail to compile.

This would be infinitely preferable!

Cheers,
mwh

-- 
  I like silliness in a MP skit, but not in my APIs. :-)
                                       -- Guido van Rossum, python-dev