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From: Joshua Landau <joshua.landau.ws@gmail.com>
Date: Mon, 24 Jun 2013 21:40:47 +0100
Subject: Re: Is this PEP-able? fwhile
To: jimjhb@aol.com
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On 24 June 2013 20:52,  <jimjhb@aol.com> wrote:
> Syntax:
>
> fwhile X in ListY and conditionZ:
>
> The following would actually exactly as:  for X in ListY:
>
> fwhile X in ListY and True:
>
> fwhile would act much like 'for', but would stop if the condition after the
> 'and' is no longer True.
>
> The motivation is to be able to make use of all the great aspects of the
> python 'for' (no indexing or explict
> end condition check, etc.) and at the same time avoiding a 'break' from the
> 'for'.

There is one good reason not to use breaks: itertools.
I often prefer a for-over-a-properly-constrained-iterable to a
for-with-a-break, but there's no real reason to ever prefer a while.

That said, why add this to the syntax when there's already
functionality that gives you what you want? Just use
itertools.takewhile as Ian Kelly says.

> (NOTE:  Many people are being taught to avoid 'break' and 'continue' at all
> costs, so they instead convert
> the clean 'for' into a less-clean 'while'.  Or they just let the 'for' run
> out.  You can argue against this teaching
> (at least for Python) but that doesn't mean it's not prevalent and
> prevailing.)

We shouldn't make a language around "people are taught the language
badly - let us accommodate for their bad practices!"

> [People who avoid the 'break' by functionalizing an inner portion of the
> loop are just kidding themselves and making
> their own code worse, IMO.]
>
> I'm not super familiar with CPython, but I'm pretty sure I could get this up
> and working without too much effort.
> The mandatory 'and' makes sense because 'or' would hold the end value valid
> (weird) and not accomplish much.
> The condition itself could of course have multiple parts to it, including
> 'or's.
>
> It's possible the name 'fwhile' is not optimal, but that shouldn't affect
> the overall merit/non-merit of the concept.

"Possible"? It's more than just possible, *wink*.

> Comments and Questions welcome.