> This could also be resolved with any &/or all i.e.:
>
> if any([foo in foobar, bar in foobar, baz in foobar]):
>
> Or even:
>
> if any([l in foobar for l in [foo, bar, baz]]
The goal was to have simpler syntax not a harder one, even if this already
works this can't be said simpler (I even personaly find that harder and way
less eyes pleasent).
If the goal is to have something that works actually the default is cleaner:
if foo in foobar or bar in foobar or baz in foobar:
Le mer. 1 janv. 2020 à 08:35, Steve Barnes <gadgetst...@live.co.uk> a
écrit :
> This could also be resolved with any &/or all i.e.:
>
> if any([foo in foobar, bar in foobar, baz in foobar]):
>
> Or even:
>
> if any([l in foobar for l in [foo, bar, baz]])
>
> but I would like to suggest allowing any & all to take more than a single
> argument,, i.e. if there are multiple arguments they are all tested for
> truth but if a single argument then it must be an iterable.
>
> Steve Barnes
>
> P.S. Happy New Year & RIP Python 2.
>
> -----Original Message-----
> From: Steven D'Aprano <st...@pearwood.info>
> Sent: 01 January 2020 02:01
> To: python-ideas@python.org
> Subject: [Python-ideas] Re: more readable "if" for multiple "in" condition
>
> On Tue, Dec 31, 2019 at 05:25:51PM +0200, Serhiy Storchaka wrote:
>
> > 31.12.19 08:20, iman.h.a.kha...@gmail.com пише:
>
> [...]
> > >if foo or bar or baz in foobar:
> > > pass
>
> [...]
> > >if foobar is foo or bar or baz:
> > > pass
>
> > This looks like an interesting idea for a completely new programming
> > language (together with "when" proposed as an alias of "if" in the
> > neighbor thread). Unfortunately it is not compatible with existing
> > Python syntax.
>
> I agree with Serhiy that this is a very interesting idea, and that it is
> not compatible with existing Python syntax. As many others have already
> pointed out, the suggested syntax already has meaning.
>
> If this were to work at all, it ought to work for all comparison
> operators, not just `in` and `is`.
>
> Because so much of Python's grammer is very English-like, it is a very
> common newbie mistake to assume that conjunctions work the same way. I have
> seen newbies write code like this:
>
> spam and eggs in sandwich
>
> expecting it to mean `spam in sandwich and eggs in sandwich`. And despite
> 20+ years of using Python, I still sometimes find myself typing
>
> spam or eggs is None
>
> when I am thinking `spam is None or eggs is None`. So I think that this
> sort of English-like semantics would be a natural fit for Python. I just
> don't see a good way to retro-fit it into the language without breaking
> existing code.
>
> I don't think that many English speakers will have trouble with the intent
> of such clauses as:
>
> if "Simon Pegg" and "Nick Frost" or "Dwayne Johnson" in movie.cast:
> go_see_movie()
>
> The problem isn't that the syntax is unreadable but that it already has a
> meaning in Python, so there is an ambiguity that requires semantic
> understanding, not just syntax, to resolve. We can resolve it in the movie
> cast example, because it is something we'd say in English where the intent
> is clear. But other examples remain ambiguous:
>
> if func(arg)[1] and db[key] or obj.attr > expression
>
> # Does this mean...?
> (1) (func(arg)[1] > expression)
> and (db[key] > expression)
> or (obj.attr > expression)
>
> (2) func(arg)[1]
> and db[key]
> or (obj.attr > expression)
>
> The first has the virtue that `expression` is only evaluated once, but the
> second is the existing meaning and we can't change that without breaking
> code.
>
> So I fear that, no matter how newbie errors this would prevent, no matter
> how English-like it would be, and no matter that the suggested alternative
> helps DRY (Don't Repeat Yourself), we're stuck with the existing semantics
> of the syntax.
>
> I would love to be proven wrong, but I don't think that there is any
> natural, English-like, backwards-compatible way to add this sort of
> "grouped/delayed conjunctions" into Python.
>
> Adding additional keywords like OR and AND isn't very satisfactory,
> because newbies will continue to use the wrong keyword.
>
> The solution I like the best would be if we had an additional kind of
> bracket, we could explicitly group the alternatives:
>
> if ¿"Simon Pegg" and "Nick Frost" or "Dwayne Johnson"? in movie.cast:
> go_see_movie()
>
> I am not seriously proposing ¿ ? as bracketing characters, just using them
> as a placeholder.
>
> But honestly, the benefit here is relatively small. Newbies will forget to
> use the ¿? brackets and get the wrong answer, and now with the walrus
> operator we can partially solve the DRY problem:
>
> if "Simon Pegg" in C:=movie.cast and "Nick Frost" in C or "Dwayne
> Johnson" in C:
> go_see_movie()
>
> Often there are straight-forward alternatives:
>
> # ¿spam and eggs? is None
> spam is eggs is None
>
> or one can use the any() and all() builtins. So the overall benefit is
> moderate (not zero) and the difficulty in making it work is high (but
> probably not impossible).
>
> [Aside: one of the oddities of English is that "conjunctions" are words
> which join phrases (and, or, but, if, as ...) but some conjunctions are
> conjunctions (and) while others are disjunctions (or).]
>
>
> --
> Steven
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