Re: Is this PEP-able? fwhile

Discussion in 'Python' started by Joshua Landau, Jun 24, 2013.

  1. On 24 June 2013 20:52, <> 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.
    Joshua Landau, Jun 24, 2013
    #1
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