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Date: Mon, 24 Jun 2013 18:13:23 -0500
From: Tim Chase <python.list@tim.thechases.com>
To: =?UTF-8?B?RsOhYmlv?= Santos <fabiosantosart@gmail.com>
Subject: Re: Is this PEP-able? fwhile
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Xref: csiph.com comp.lang.python:49105

On 2013-06-24 23:39, F=C3=A1bio Santos wrote:
> On 24 Jun 2013 23:35, "Tim Chase" wrote:
> > On 2013-06-25 07:38, Chris Angelico wrote:
> > > Python has no issues with breaking out of loops, and even has
> > > syntax specifically to complement it (the 'else:' clause). Use
> > > break/continue when appropriate.
> >
> > from minor_gripes import breaking_out_of_nested_loops_to_top_level
>=20
> for x, y in itertools.product(range(width), range(height)):

This works nicely for certain use cases, but if there's additional
processing that needs to be done in the outer loops, it starts to get
hairy.  As Ian Kelly mentions, I could really dig a labeled
break/continue in Python (it's one of the few ideas I like that Java
made pretty popular; though I can't say I particularly care for
Java's implementation).  I'd love to see something like a decorator
where you could do things like the following pseudocode:

  @toplevel
  for i in range(height):
    for j in range(width):
      for component in data[i,j]:
        if condition:
          continue toplevel
        elif other_condition:
          break toplevel
        else:
          other processing

I'm not sure such a feature would ever arrive, but it would make it
easier than the current recommendation which is usually to either (1)
make inner loops into functions from which you can return; or (2)
raise a custom exception and then catch it in the outer loop.

-tkc