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Re: Is this PEP-able? fwhile

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  Re: Is this PEP-able? fwhile jimjhb@aol.com - 2013-06-24 16:51 -0400

#49084 — Re: Is this PEP-able? fwhile

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I find itertools clumsy and wordy.  You shouldn't have to have a lambda expression just to break out of a for!

I agree to not cater to bad practices, but if a clean improvement is possible it will practically help code
overall, even if theoretically people shouldn't be adopting a practice (don't use breaks) to the wrong
circumstance (the python 'for' is not like other fors in other languages).


-Jim



-----Original Message-----
From: Joshua Landau <joshua.landau.ws@gmail.com>
To: jimjhb <jimjhb@aol.com>
Cc: python-list <python-list@python.org>
Sent: Mon, Jun 24, 2013 4:41 pm
Subject: Re: Is this PEP-able? fwhile


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.

 

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