[Python-Dev] Sets, Dictionaries

[David Mertz]

I agree with everything Steven says. But it's true that even as a 20-year
Python user, this is an error I make moderately often when I want an empty
set... Notwithstanding that I typed it thousands of times before sets even
existed (and still type it when I want an empty dictionary).

That said, I've sort of got in the habit of using the type initializers:

x = set()
y = dict()
z = list()

I feel like those jump out a little better visually. But I'm inconsistent
in my code.

On Thu, Mar 29, 2018, 2:03 AM Steven D'Aprano <steve at pearwood.info> wrote:

> Hi Julia, and welcome!
>
> On Wed, Mar 28, 2018 at 09:14:53PM -0700, Julia Kim wrote:
>
> > My suggestion is to change the syntax for creating an empty set and an
> > empty dictionary as following.
> >
> > an_empty_set = {}
> > an_empty_dictionary = {:}
> >
> > It would seem to make more sense.
>
> Indeed it would, and if sets had existed in Python since the beginning,
> that's probably exactly what we would have done. But unfortunately they
> didn't, and {} has meant an empty dict forever.
>
> The requirement to keep backwards-compatibility is a very, very hard
> barrier to cross. I think we all acknowledge that it is sad and a little
> bit confusing that {} means a dict not a set, but it isn't sad or
> confusing enough to justify breaking millions of existing scripts and
> applications.
>
> Not to mention the confusing transition period when the community would
> be using *both* standards at the same time, which could easily last ten
> years.
>
> Given that, I think we just have to accept that having to use set() for
> the empty set instead of {} is a minor wart on the language that we're
> stuck with.
>
> If you disagree, and think that you have a concrete plan that can make
> this transition work, we'll be happy to hear it, but you'll almost
> certainly need to write a PEP before it could be accepted.
>
> https://www.python.org/dev/peps/
>
>
> Thanks,
>
> --
> Steve
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