[Python-ideas] 'where' statement in Python?

[Nick Coghlan]

On Wed, Jul 21, 2010 at 12:56 PM, Chris Rebert <pyideas at rebertia.com> wrote:
> On Tue, Jul 20, 2010 at 3:13 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
>> On Wed, Jul 21, 2010 at 6:13 AM, Alex Light <scialexlight at gmail.com> wrote:
>>> i would use as because this whole where clause acts very similarly to a
>>> context manager in that it sets a variable to a value for a small block
>>
>> No, the idea is for the indented suite to be a perfectly normal suite
>> of Python code. We want to be able to define functions, classes, etc
>> in there. Inventing a new mini-language specifically for these clauses
>> would be a bad idea (and make them unnecessarily hard to understand)
> <snip>
> Did you not read Nick's reply yet when you wrote this, or...?

Alex actually has a reasonable point here: break, continue, yield and
return actually don't make sense in the top-level of the given clause
(since it is conceptually all one statement).

For break and continue, they will naturally give a SyntaxError with
the proposed implementation (for "'break' outside loop" or "'continue'
not properly in loop", just to be randomly inconsistent).

yield and return (at the level of the given clause itself) will need
to be disallowed explicitly by the compiler (similar to the "'return'
outside function" and "'yield' outside function" errors you get if you
attempt to use these keywords in a class or module scope).

There are also some subtleties as to whether the given clause is
compiled as a closure or not (my current thoughts are that it should
be compiled as a closure when defined in a function scope, but like a
class scope when defined in a class or module scope).

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia