On Mon, Sep 28, 2020 at 08:19:01PM -0700, Ben Rudiak-Gould wrote:
> Maybe a singleton that supported no useful operations, not even __eq__ or
> __bool__, would be sufficiently inconvenient that it would only be used for
> defaults and "is" tests for said defaults.
NotImplemented is halfway there:
On 29/09/20 4:19 pm, Ben Rudiak-Gould wrote:
it's worth
mentioning that Haskell has tuples of length 0, 2, 3, ..., but no tuples
of length 1. Tuples are meant for putting n values where 1 value is
expected, and when n=1 you just put the value there.
To elaborate on that a bit, the length of a
On Sun, Sep 27, 2020 at 2:18 PM MRAB wrote:
> Consider, for example, the use-case of a function that has an optional
> parameter and you want a way to know whether an argument has been
> provided but None is a valid value that could be passed in.
>
> Having a singleton such as Missing would be he
On Mon, 28 Sep 2020 at 15:45, Eric Wieser wrote:
>
> Would another option be to just stop using the tuple-less index in the
> presence of new syntax - so by example,
I don't think it would be a reliable approach. Now you end up with a
"randomly" occurring special case depending on how it's invok
On 2020-09-28 06:51, Chris Angelico wrote:
On Mon, Sep 28, 2020 at 3:33 PM Christopher Barker wrote:
As for using an empty tuple, thanks Guido for laying out the logic so succinctly, and it
does make it pretty simple that only the one index case is special. Nevertheless, I think
most folks ex
Would another option be to just stop using the tuple-less index in the presence
of new syntax - so by example,
```
SYNTAXINDEX KWARGS
d[*[]]() {}
d[*[],] () {}
d[**{}] () {}
d[**{},] () {}
d[foo=1] () {'foo': 1}
d[foo=1,] () {'foo
On Mon, Sep 28, 2020 at 3:33 PM Christopher Barker wrote:
> As for using an empty tuple, thanks Guido for laying out the logic so
> succinctly, and it does make it pretty simple that only the one index case is
> special. Nevertheless, I think most folks expect the special case to be at
> the en
On Sun, Sep 27, 2020 at 1:51 PM David Mertz wrote:
> On Sun, Sep 27, 2020 at 10:41 AM Stefano Borini
> wrote:
>
>> I kept the tuple as the accepted option, but I am personally open to
>> NoIndex as well. I am not sure how the SC would take a non-hashable, new
>> constant to be
>> honest, for suc
On Sun, Sep 27, 2020 at 4:29 AM Stefano Borini
wrote:
> ```
> >>> obj[**d] = "foo" # no kwd arguments provided here
> ```
> I committed yesterday the following proposal
>
> https://github.com/python/peps/pull/1622
>
> But to be honest I am not sure if we should disallow these two constructs
> ``
On 2020-09-27 21:47, David Mertz wrote:
On Sun, Sep 27, 2020 at 10:41 AM Stefano Borini
mailto:stefano.bor...@gmail.com>> wrote:
I kept the tuple as the accepted option, but I am personally open to
NoIndex as well. I am not sure how the SC would take a non-hashable,
new constant to
On Sun, Sep 27, 2020 at 10:41 AM Stefano Borini
wrote:
> I kept the tuple as the accepted option, but I am personally open to
> NoIndex as well. I am not sure how the SC would take a non-hashable, new
> constant to be
> honest, for such a specific use case.
>
My "vote" is for NoIndex. I suggest
On Sun, 27 Sep 2020 at 12:28, Stefano Borini wrote:
> I am not sure. I am on the fence on many topics. There seem to be no
> clear solution on many of them, it boils down to taste and compromise.
> In any case, I listen to all proposals (although with a small delay).
> I am working on the sentinel
On Sat, Sep 26, 2020 at 22:57 Steven D'Aprano wrote:
> Christopher, with the greatest respect, it is really demoralising for me
> to explain this issue something like three, four, maybe five times now
> (I'm not going to go back and count), including this thread which is
> specifically about this
On Sun, 27 Sep 2020 at 05:06, Ricky Teachey wrote:
>>> obj[**d] = "foo" # no kwd arguments provided here
I committed yesterday the following proposal
https://github.com/python/peps/pull/1622
But to be honest I am not sure if we should disallow these two constructs
d[*()]
d[**{}]
as equivale
On Sun, Sep 27, 2020 at 7:08 PM Steven D'Aprano wrote:
> 1. Fill in a default index with one of:
>
> a. None
> b. empty tuple ()
> c. NotImplemented
> d. a new, unhashable builtin Missing or NoIndex
>
> 1d. avoids any chance of that, but requires a new builtin;
>
An interesting and very good poin
On Sat, Sep 26, 2020 at 07:12:00PM -0400, Ricky Teachey wrote:
> Another inconsistency is that the case of keyword arguments only would bind
> the RHS value to the first positional argument, which is the index, and not
> the value. I think this is what Guido was referring to when he responded
> tal
On 27/09/20 7:10 pm, Steven D'Aprano wrote:
kw = get_keywords() # oops, this returns an empty dict
obj[**kw] = value
If an explicit d[] is going to be a compile-time error, maybe
anything that has the same effect at run time should be an
error too?
--
Greg
__
On Sat, Sep 26, 2020 at 10:43:23PM -0400, Ricky Teachey wrote:
> The problem is that there is lots of existing code like this:
>
> def __setitem__(self, index, value): ...
>
> But the new features will almost certainly lead people to write new code
> like this:
>
> d={}
> obj[**d] = "foo" # no
On Sat, Sep 26, 2020 at 03:48:42PM -0700, Christopher Barker wrote:
> On Fri, Sep 25, 2020 at 11:50 PM Steven D'Aprano
> wrote:
> >>
> >> 1. We have to pass a sentinel to the setitem dunder if there is no
> >> positional index passed.
>
>
> I still don't follow this logic -- why can't nothing be
On Sat, Sep 26, 2020 at 11:49 PM Guido van Rossum wrote:
> On Sat, Sep 26, 2020 at 7:44 PM Ricky Teachey wrote:
>
>> The problem is that there is lots of existing code like this:
>>
>> def __setitem__(self, index, value): ...
>>
>> But the new features will almost certainly lead people to write
On Sat, Sep 26, 2020 at 7:44 PM Ricky Teachey wrote:
> The problem is that there is lots of existing code like this:
>
> def __setitem__(self, index, value): ...
>
> But the new features will almost certainly lead people to write new code
> like this:
>
> d={}
> obj[**d] = "foo" # no kwd argumen
On Sat, Sep 26, 2020, 11:30 PM Greg Ewing
wrote:
> On 27/09/20 3:43 pm, Ricky Teachey wrote:
> > telling people "either provide a default argument for
> > both index AND value in your __setitem__ method, or neither" is also a
> > perfectly legitimate way forward.
>
> Giving the value parameter of
On 27/09/20 3:43 pm, Ricky Teachey wrote:
telling people "either provide a default argument for
both index AND value in your __setitem__ method, or neither" is also a
perfectly legitimate way forward.
Giving the value parameter of a __setitem__ a default seems like a
weird thing to do, since u
On Sat, Sep 26, 2020 at 10:43 PM Ricky Teachey wrote:
> ...which, if someone does this arbitrarily against classes that use the
> existing kind of code I gave at the first, will call (if the sentinel is ()
> ):
>
> obj.__setitem__(())
>
> ...which could have all kinds of weird effects rather than
On Sat, Sep 26, 2020 at 10:30 PM Ben Rudiak-Gould
wrote:
> I don't understand the problem here.
>
> d[p=q] --> d.__{get,set,del}item__((), ..., p=q)
> d[1, p=q] --> d.__{get,set,del}item__((1), ..., p=q)
> d[1, 2, p=q] --> d.__{get,set,del}item__((1, 2), ..., p=q)
> d[1, 2,
I don't understand the problem here.
d[p=q] --> d.__{get,set,del}item__((), ..., p=q)
d[1, p=q] --> d.__{get,set,del}item__((1), ..., p=q)
d[1, 2, p=q] --> d.__{get,set,del}item__((1, 2), ..., p=q)
d[1, 2, 3, p=q] --> d.__{get,set,del}item__((1, 2, 3), ..., p=q)
d[1, 2,
On Sun, Sep 27, 2020 at 8:49 AM Christopher Barker wrote:
>
>
> On Fri, Sep 25, 2020 at 11:50 PM Steven D'Aprano wrote:
> >>
> >> 1. We have to pass a sentinel to the setitem dunder if there is no
> >> positional index passed.
>
>
> I still don't follow this logic -- why can't nothing be passed?
Another inconsistency is that the case of keyword arguments only would bind
the RHS value to the first positional argument, which is the index, and not
the value. I think this is what Guido was referring to when he responded
talking about introspection being required? Not sure.
in any case, to me
On Fri, Sep 25, 2020 at 11:50 PM Steven D'Aprano
wrote:
>>
>> 1. We have to pass a sentinel to the setitem dunder if there is no
>> positional index passed.
I still don't follow this logic -- why can't nothing be passed? The dunders
either require an index or they don't, would that be just like
On Fri, Sep 25, 2020 at 11:26 PM Ricky Teachey wrote:
> On Sat, Sep 26, 2020 at 1:51 AM Guido van Rossum wrote:
>
>> But this requires introspection.
>>
>
> I'm sorry Guido I'm staring at your message and reread mine several times
> and I don't understand where introspection is required. It seem
On Fri, Sep 25, 2020 at 08:52:45PM -1000, David Mertz wrote:
> On Fri, Sep 25, 2020, 5:49 PM Steven D'Aprano
>
> > Since both None and () are likely to be legitimate indexes, and
> > NotImplemented is less likely to be such, I think this supports using
> > NotImplemented.
> >
>
> I think your arg
On Sat, Sep 26, 2020 at 01:43:18AM -0400, Ricky Teachey wrote:
> On Fri, Sep 25, 2020 at 11:50 PM Steven D'Aprano
> wrote:
>
> > TL;DR:
> >
> > 1. We have to pass a sentinel to the setitem dunder if there is no
> > positional index passed. What should that sentinel be?
> >
>
> Isn't there a prob
On Fri, Sep 25, 2020, 5:49 PM Steven D'Aprano
> Since both None and () are likely to be legitimate indexes, and
> NotImplemented is less likely to be such, I think this supports using
> NotImplemented.
>
I think your arguments for NotImplemented vs None or () are solid. But I'm
having trouble cro
On Sat, Sep 26, 2020 at 1:51 AM Guido van Rossum wrote:
> But this requires introspection.
>
I'm sorry Guido I'm staring at your message and reread mine several times
and I don't understand where introspection is required. It seems like all
the parser has to do is what it has always done-- pass
But this requires introspection.
On Fri, Sep 25, 2020 at 22:46 Ricky Teachey wrote:
> On Fri, Sep 25, 2020 at 11:50 PM Steven D'Aprano
> wrote:
>
>> TL;DR:
>>
>>
>>
>>
>>
>> 1. We have to pass a sentinel to the setitem dunder if there is no
>>
>>
>> positional index passed. What should that sen
On Fri, Sep 25, 2020 at 11:50 PM Steven D'Aprano
wrote:
> TL;DR:
>
> 1. We have to pass a sentinel to the setitem dunder if there is no
> positional index passed. What should that sentinel be?
>
Isn't there a problem with this starting assumption?
Say that I have item dunder code of the signatu
Change of subject line as I wish to focus on a single critical point of
the PEP: keyword-only subscripts.
TL;DR:
1. We have to pass a sentinel to the setitem dunder if there is no
positional index passed. What should that sentinel be?
* None
* the empty tuple ()
* NotImplemented
* somethi
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