subject:"\[Python\-ideas\] Re\: The name Ellipsis should be a constant"

On Mon, May 31, 2021 at 11:41 PM Steven D'Aprano 
wrote:

> It's pretty standard behaviour for Python.  Right now, `eval(repr(...))`
> works unless you have shadowed the name
> Ellipsis.
>
> >>> err = ValueError('something went wrong')
> >>> ValueError = list
> >>> eval(repr(err))
> ['s', 'o', 'm', 'e', 't', 'h', 'i', 'n', 'g', ' ', 'w', 'e', 'n',
> 't', ' ', 'w', 'r', 'o', 'n', 'g']
>

Yeah, my surprise was kind of a "thinko." I think I was thinking of the
eval() separately from the repr().  But nonetheless, the idempotency
question still arises, and I believe is reasonable.

> Unless we make the ellipsis object `...` callable. But that doesn't help
> us if the name Ellipsis has been rebound. Then it will call the rebound
> object.
>

> Let's change the behavior of the Ellipsis object slightly to have either a
> .__call__() or .__getitem__() method that returns itself

That was exactly what I suggested.  The three dots themselves, which CANNOT
be bound to any other object, could be callable or indexable.  If you
define a class Ellipsis to use that name, it makes no difference to
`repr(...) == "...[Ellipsis]"`  Note that I am NOT proposing
`Ellipsis(...)` as the repr for EXACTLY that reason.

> Not every builtin needs a mollyguard to protect against misuse.
>

I'm not likely to rebind `Ellipsis` so that's not really my concern.
Rather, I'm interested in the point André Roberge started the thread with.
The repr of '...' should be more self-explanatory to beginners.  It's
basically co-opting the square brackets or parenthesis to mean something
that doesn't really have anything to do with calling or indexing in order
to have a repr—in tracebacks specifically, but elsewhere also—that reminds
users of the connection between `...` and `Ellipsis`.

-- 
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Steven D'Aprano

On Mon, May 31, 2021 at 09:12:42PM -0400, David Mertz wrote:
> >
> > I think you are going against the design of the language here. With only
> >
> a handful of critical exceptional cases (None, True, False are the only
> > ones that come to mind), names can be rebound.
> >
> 
> The following genuinely surprised me.  I was trying to show something
> different in reply, but I think the actual behavior makes the point even
> more:
[...]
> This is *strange* behavior.  I don't expect every sequence of characters to
> round trip `eval(repr())`, but I kinda expect it to be mostly idempotent.

It's pretty standard behaviour for Python.

>>> err = ValueError('something went wrong')
>>> ValueError = list
>>> eval(repr(err))
['s', 'o', 'm', 'e', 't', 'h', 'i', 'n', 'g', ' ', 'w', 'e', 'n', 
't', ' ', 'w', 'r', 'o', 'n', 'g']

The repr of an object tells you what the object thinks it is called; but 
`eval` evaluates the given source code according to whatever name 
bindings happen to exist at the time, which can shadow or monkey-patch 
the names that were used to generate the object in the first place.

>>> eval(repr(NotImplemented))
NotImplemented
>>> NotImplemented = len
>>> eval(repr(str.__lt__('', None)))

The lesson here is not to rebind names if you don't want eval to use the 
rebound names :-)

Right now, `eval(repr(...))` works unless you have shadowed the name 
Ellipsis. If we make the proposed changed, it will call whatever 
arbitrary object was bound to Ellipsis, so the best you can hope for is 
a TypeError:

>>> eval('Ellipsis (...)')
Traceback (most recent call last):
  File "", line 1, in 
  File "", line 1, in 
TypeError: 'ellipsis' object is not callable

Unless we make the ellipsis object `...` callable. But that doesn't help 
us if the name Ellipsis has been rebound. Then it will call the rebound 
object.

I have to emphasise that this is standard, normal behaviour, and I still 
don't know why we are disturbed by Ellipsis behaving like nearly 
everything else in Python. The only oddity is that unlike most things, 
Ellipsis also has a special symbol `...` that most objects don't have.

[...]
> Let's change the behavior of the Ellipsis object slightly to have either a
> .__call__() or .__getitem__() method that returns itself, no matter what
> argument is passed.

"Errors should never pass silently."

class Ellipse(Shape):
...

myshape = Ellipsis(mysquare)  # oops
# much later on...
myshape.draw()  # TypeError

Okay, it's a bit of a contrived set of circumstances, but it 
demonstrates the idea that functions should not ignore their arguments. 
Exceptions should, if possible, occur as close as possible to the actual 
error (the use of Ellipsis instead of Ellipse).

If the parameter to a function has no effect, it shouldn't be a 
parameter. If you pass an invalid argument to the (hypothetical) 
callable Ellipsis, it should raise TypeError immediately, not ignore the 
argument.

So we're trying to fix an issue of next to no practical importance, that 
doesn't really affect anyone, by building in more complexity and weird 
corner cases in the language. I don't think that's a good trade off. 
Shadowing and monkey-patching are advanced techniques, and we shouldn't 
demand the language protect newbies who accidentally shadow the built-in 
Ellipsis and then try to use eval.

Not every builtin needs a mollyguard to protect against misuse.

-- 
Steve
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[Python-ideas] Re: The name Ellipsis should be a constant

On Mon, May 31, 2021 at 9:12 PM David Mertz  wrote:

> >>> foo = "bar"
>
>>> eval(repr(foo)) == eval(repr(eval(repr(foo
> True
> >>> eval(repr(None)) == eval(repr(eval(repr(None
> True
>
> Let's change the behavior of the Ellipsis object slightly to have either a
> .__call__() or .__getitem__() method that returns itself, no matter what
> argument is passed.
>
> >>> repr(...)
> ...[Ellipsis]
>
...(Ellipsis)
>
> I don't know which looks better, but neither look terrible to me.  That
> would produce a more explanatory repr() while also preserving idempotence.
>

Oh... just in case I wasn't clear, `Ellipsis.__repr__()` would obviously
need to be changed slightly as well along with adding .__call__() or
.__getitem__() for this to work.


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[Python-ideas] Re: The name Ellipsis should be a constant

>
> I think you are going against the design of the language here. With only
>
a handful of critical exceptional cases (None, True, False are the only
> ones that come to mind), names can be rebound.
>

The following genuinely surprised me.  I was trying to show something
different in reply, but I think the actual behavior makes the point even
more:

>>> eval(repr(Ellipsis))
Ellipsis
>>> eval(repr(...))
Ellipsis
>>> Ellipsis = 42
>>> eval(repr(...))
42

This is *strange* behavior.  I don't expect every sequence of characters to
round trip `eval(repr())`, but I kinda expect it to be mostly idempotent.

>>> foo = "bar"
>>> eval(repr(foo))
'bar'
>>> eval(repr(foo)) == eval(repr(eval(repr(foo
True
>>> eval(repr(None)) == eval(repr(eval(repr(None
True

Obviously I know there are some repr()'s that cannot be eval()'d.  But this
isn't the same concern as e.g. a file handle or a user class.

I don't find this issue any huge wart in Python, but it's a funny corner.
Here's a proposal I'll throw out:

Let's change the behavior of the Ellipsis object slightly to have either a
.__call__() or .__getitem__() method that returns itself, no matter what
argument is passed.

Then we could have this behavior:

>>> repr(...)
...[Ellipsis]

Or

>>> repr(...)
...(Ellipsis)

I don't know which looks better, but neither look terrible to me.  That
would produce a more explanatory repr() while also preserving idempotence.


-- 
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Filipe Laíns

On Mon, 2021-05-31 at 11:37 -0300, André Roberge wrote:
> In Python `...` is referred to as `Ellipsis` and cannot be assigned to. 
> Yet, one can assign any value to the name `Ellipsis`.
> 
> Consider the following:
> 
> ```
> > > > ...
> Ellipsis
> > > > ... == Ellipsis
> True
> > > > Ellipsis
> Ellipsis
> > > > Ellipsis = 3
> > > > Ellipsis
> 3
> > > > ... = 4
>   File "", line 1
>     ... = 4
>     ^
> SyntaxError: cannot assign to Ellipsis
> > > >   # But I just did assign a new value to the name Ellipsis above.
> > > > Ellipsis
> 3    
> > > > ...
> Ellipsis
> > > > ... == Ellipsis
> False
> ```
> 
> For consistency, `Ellipsis` (the name) should **always** refer to the same
> object that `...` refers to, so that both could not be assigned a new value.
> 

Perhaps Ellipsis could get the same treatment as None here, but I am not sure if
there's enough reasoning to justify that, especially considering that it would
be a backwards incompatible change.

Do you have any use-cases that would warrant such a thing? I find it incredibly
hard to justify this proposal.

Cheers,
Filipe Laíns


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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Steven D'Aprano

On Mon, May 31, 2021 at 10:55:08PM +0100, MRAB wrote:

> >>>> a = []; a.append(a); a
> >[[...]]
> >>>> [[...]]
> >[[Ellipsis]]
> >
> Why is it 3 dots anyway? As we've already ascribed a meaning to 3 dots, 
> why not use 4 dots in this use?

Three dots for ommitted text is standard in English. Four dots is an 
ellipsis followed by a full stop. We could go against that convention 
(Python is not English, although it is based closely on many English 
conventions) but honestly I think that any change in this area is of 
such little benefit that it's not worth the potential disruption to 
documentation and doctests.

-- 
Steve
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Steven D'Aprano

On Mon, May 31, 2021 at 12:36:34PM -0300, André Roberge wrote:

> Thinking some more about it, perhaps the confusion would be sufficiently
> reduced if the repr of '...' would be 'Ellipsis (...)', and use this repr
> to appear in error messages rather than simply the name Ellipsis.

I think you are going against the design of the language here. With only 
a handful of critical exceptional cases (None, True, False are the only 
ones that come to mind), names can be rebound.

>>> type(4)

>>> int = list
>>> type(4)

>>> int('123')
['1', '2', '3']

Objects are not their name, and their name is not the object. Objects do 
not know the name or names they are bound to.

`...` is not a name, it is a syntactic symbol that is hard coded in the 
interpreter to the object which we popularly call "Ellipsis". You can't 
assign to the symbol any more than you can assign to the symbol `+`.

On the other hand, `Ellipsis` is just a name. Like nearly all names in 
Python, you can rebind it or delete it. Rebinding the name doesn't 
affect the object `...`. It still knows itself as Ellipsis, no matter 
what names happen to be bound to it in some namespace or another.

(Analogy: you would probably still think of yourself as André even if we 
all started to call you Bruce.)

We *could* single out Ellipsis for special treatment, like None, True 
and False, but what's so special about Ellipsis that we should bother?

The bottom line here is that the *name* "Ellipsis" is not special. It's 
just a name, like int, TypeError, and all the rest.

If you want to make Ellipsis a keyword, like None, True and False, you 
would need some good reason for it.

-- 
Steve
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread MRAB

On 2021-05-31 21:19, Serhiy Storchaka wrote:

31.05.21 22:46, Chris Angelico пише:

Originally, the notation "..." could only be used inside a subscript,
and anywhere else, you'd have to spell it "Ellipsis". Now that you can
use "..." anywhere, would it be worth switching the repr to just be
that?

How would you then distinguish a recursive list from a list containing
Ellipsis?

>>> a = []; a.append(a); a
[[...]]
>>> [[...]]
[[Ellipsis]]

Why is it 3 dots anyway? As we've already ascribed a meaning to 3 dots, 
why not use 4 dots in this use?

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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Brendan Barnwell

On 2021-05-31 12:46, Chris Angelico wrote:

On Tue, Jun 1, 2021 at 5:40 AM David Mertz wrote:

I think making 'Ellipsis' a reserved word is too much. The analogy with
non-reserved words like `int`, `str`, `map`, `print`, and so on, illustrate
this, I think. I.e. redefining those is likely to cause bad things to happen,
but we're consenting adults, and in the end they are just names.

However, I think improving the repr() of the Ellipsis object itself to remind
users of the connection with its special literal `...` is a great idea.

Originally, the notation "..." could only be used inside a subscript,
and anywhere else, you'd have to spell it "Ellipsis". Now that you can
use "..." anywhere, would it be worth switching the repr to just be
that?

I feel like that might be confusing. We do have things like lists
where the repr of an empty list is [], but lists are pretty basic and
ubiquitous Python objects that people usually learn about quite early.
Ellipsis is a more obscure thing so it seems worthwhile to label it
somehow rather than just giving a cryptic three dots.

--
Brendan Barnwell
"Do not follow where the path may lead. Go, instead, where there is no
path, and leave a trail."

--author unknown
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[Python-ideas] Re: The name Ellipsis should be a constant

31.05.21 23:28, Chris Angelico пише:
> Although... since that's an arbitrary placeholder, it could be changed
> to pretty much anything. Maybe <...> or something? The current repr
> may not technically be ambiguous, but it will silently do the wrong
> thing if you try to eval it. You can even ast.literal_eval(repr(a))
> and it'll appear to work.

It was already discussed in 2015 [1], but the idea of <...> was rejected
by Guido [2].

[1]
https://mail.python.org/archives/list/python-ideas@python.org/thread/T2T7WR52AYLM7R77G6QMSDSPFYWBEBCL/
[2]
https://mail.python.org/archives/list/python-ideas@python.org/thread/RAZMTY2VGVXZYIO7RTA4DVW5C7MCTWOQ/

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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Chris Angelico

On Tue, Jun 1, 2021 at 6:22 AM Serhiy Storchaka  wrote:
>
> 31.05.21 22:46, Chris Angelico пише:
> > Originally, the notation "..." could only be used inside a subscript,
> > and anywhere else, you'd have to spell it "Ellipsis". Now that you can
> > use "..." anywhere, would it be worth switching the repr to just be
> > that?
>
> How would you then distinguish a recursive list from a list containing
> Ellipsis?
>
>>>> a = []; a.append(a); a
>[[...]]
>>>> [[...]]
>[[Ellipsis]]

Good point, didn't think of that.

Although... since that's an arbitrary placeholder, it could be changed
to pretty much anything. Maybe <...> or something? The current repr
may not technically be ambiguous, but it will silently do the wrong
thing if you try to eval it. You can even ast.literal_eval(repr(a))
and it'll appear to work.

Not a huge deal whichever way, though. The token "..." is used in a
variety of non-ellipsis ways, such as doctest, and that isn't
inherently a problem.

ChrisA
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[Python-ideas] Re: The name Ellipsis should be a constant

31.05.21 22:59, Jelle Zijlstra пише:
> Why isn't `repr(...)` just `...`?

Because it would confuse with reprs for recursive collections.

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[Python-ideas] Re: The name Ellipsis should be a constant

31.05.21 22:46, Chris Angelico пише:
> Originally, the notation "..." could only be used inside a subscript,
> and anywhere else, you'd have to spell it "Ellipsis". Now that you can
> use "..." anywhere, would it be worth switching the repr to just be
> that?

How would you then distinguish a recursive list from a list containing
Ellipsis?

   >>> a = []; a.append(a); a
   [[...]]
   >>> [[...]]
   [[Ellipsis]]

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[Python-ideas] Re: The name Ellipsis should be a constant

+1

On Tue, 2021-06-01 at 05:46 +1000, Chris Angelico wrote:
> On Tue, Jun 1, 2021 at 5:40 AM David Mertz  wrote:
> > 
> > I think making 'Ellipsis' a reserved word is too much.  The analogy
> > with non-reserved words like `int`, `str`, `map`, `print`, and so
> > on, illustrate this, I think.  I.e. redefining those is likely to
> > cause bad things to happen, but we're consenting adults, and in the
> > end they are just names.
> > 
> > However, I think improving the repr() of the Ellipsis object itself
> > to remind users of the connection with its special literal `...` is
> > a great idea.
> > 
> 
> Originally, the notation "..." could only be used inside a subscript,
> and anywhere else, you'd have to spell it "Ellipsis". Now that you
> can
> use "..." anywhere, would it be worth switching the repr to just be
> that?
> 
> ChrisA
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Jelle Zijlstra

El lun, 31 may 2021 a las 12:40, David Mertz () escribió:

> I think making 'Ellipsis' a reserved word is too much.  The analogy with
> non-reserved words like `int`, `str`, `map`, `print`, and so on, illustrate
> this, I think.  I.e. redefining those is likely to cause bad things to
> happen, but we're consenting adults, and in the end they are just names.
>
> However, I think improving the repr() of the Ellipsis object itself to
> remind users of the connection with its special literal `...` is a great
> idea.
>
>
> Why isn't `repr(...)` just `...`?
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Chris Angelico

On Tue, Jun 1, 2021 at 5:40 AM David Mertz  wrote:
>
> I think making 'Ellipsis' a reserved word is too much.  The analogy with 
> non-reserved words like `int`, `str`, `map`, `print`, and so on, illustrate 
> this, I think.  I.e. redefining those is likely to cause bad things to 
> happen, but we're consenting adults, and in the end they are just names.
>
> However, I think improving the repr() of the Ellipsis object itself to remind 
> users of the connection with its special literal `...` is a great idea.
>

Originally, the notation "..." could only be used inside a subscript,
and anywhere else, you'd have to spell it "Ellipsis". Now that you can
use "..." anywhere, would it be worth switching the repr to just be
that?

ChrisA
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[Python-ideas] Re: The name Ellipsis should be a constant

I think making 'Ellipsis' a reserved word is too much.  The analogy with
non-reserved words like `int`, `str`, `map`, `print`, and so on, illustrate
this, I think.  I.e. redefining those is likely to cause bad things to
happen, but we're consenting adults, and in the end they are just names.

However, I think improving the repr() of the Ellipsis object itself to
remind users of the connection with its special literal `...` is a great
idea.

On Mon, May 31, 2021 at 3:27 PM André Roberge 
wrote:

>
>
> On Mon, May 31, 2021 at 4:17 PM Serhiy Storchaka 
> wrote:
>
>> 31.05.21 17:37, André Roberge пише:
>> > For consistency, `Ellipsis` (the name) should **always** refer to the
>> > same object that `...` refers to, so that both could not be assigned a
>> > new value.
>>
>> Making Ellipsis a keyword will break ast.Ellipsis (and maybe some
>> third-party libraries).
>>
>
> I realized that after my initial post which is why I subsequently
> suggested that its repr should perhaps be "Ellipsis (...)".  But, I admit,
> it is a rather obscure corner case that few, if any beginners would
> encounter and be confused by the error message.
>
>
>
>>
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread André Roberge

On Mon, May 31, 2021 at 4:17 PM Serhiy Storchaka 
wrote:

> 31.05.21 17:37, André Roberge пише:
> > For consistency, `Ellipsis` (the name) should **always** refer to the
> > same object that `...` refers to, so that both could not be assigned a
> > new value.
>
> Making Ellipsis a keyword will break ast.Ellipsis (and maybe some
> third-party libraries).
>

I realized that after my initial post which is why I subsequently suggested
that its repr should perhaps be "Ellipsis (...)".  But, I admit, it is a
rather obscure corner case that few, if any beginners would encounter and
be confused by the error message.



>
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[Python-ideas] Re: The name Ellipsis should be a constant

31.05.21 17:37, André Roberge пише:
> For consistency, `Ellipsis` (the name) should **always** refer to the
> same object that `...` refers to, so that both could not be assigned a
> new value.

Making Ellipsis a keyword will break ast.Ellipsis (and maybe some
third-party libraries).

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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread André Roberge

On Mon, May 31, 2021 at 2:40 PM Guido van Rossum  wrote:

> Andre, did you have an experience where something related to Ellipsis/...
> confused you? It is not clear to me what exactly prompted you to single out
> Ellipsis (or it’s repr()?)
>

Guido, the reason why I tried is that I am working on a project called
friendly (previously named friendly-traceback) which aims to provide "easy
to understand" explanations to beginners when they encounter tracebacks.[1]

In playing with different cases involving assignments to a constant
(__debug__, None, True, False, ... and Ellipsis as '...'), I came across
this particular case which I thought was confusing: Python says that we
cannot assign to Ellipsis ... and yet we can.  I thought that the
explanation provided by cPython itself could be made a bit clearer.
The specific suggestion I made is based on the explanation *friendly*
currently gives, where it specifies that Ellipsis refers to (...).

Admittedly, this is rather a corner case.

André


With friendly, I usually strive to cover more typical cases that are
encountered by beginners, such as one example I gave at this year's PyConUS
Education summit where, given the following message:

AttributeError: partially initialized module 'turtle' has no attribute
'forward' (most likely due to a circular import)

friendly adds the following "hint":

Did you give your program the same name as a Python module?

And, upon being prompted, friendly adds the following:

I suspect that you used the name turtle.py for your program and that you
also wanted to import a
module with the same name from Python's standard library. If so, you should
use a different name for your program.

(This particular turtle is not hard-coded in friendly; any circular import
is similarly analyzed and some further explanation is provided.)

[1]  Currently, I have at least 150 different cases yielding SyntaxErrors
for which friendly can provide help (see
https://aroberge.github.io/friendly-traceback-docs/docs/html/syntax_tracebacks_en_3.8.html
for cases covered by unit tests) and probably a hundred or so of various
types of other errors. Furthermore, friendly is designed so that the
explanations can be translated into other languages; currently, every case
friendly covers has explanations available in both English and French.


> On Mon, May 31, 2021 at 08:37 André Roberge 
> wrote:
>
>>
>>
>> On Mon, May 31, 2021 at 12:20 PM MRAB  wrote:
>>
>>> On 2021-05-31 15:55, Paul Bryan wrote:
>>> > If you're proposing prevention of monkey patching Ellipsis, I think
>>> > you'll have to go all-in on all builtins.
>>> >
>>> > For example:
>>> >
>>>  str = int
>>> >
>>>  str
>>> >
>>> > 
>>> >
>>>  str == int
>>> >
>>> > True
>>> >
>>> >
>>> If you rebind str to int, the repr of str will say , so you
>>> can tell that something's happened, but the repr of ... is always
>>> 'Ellipsis', even though you've rebound Ellipsis.
>>>
>>
>> Exactly.
>>
>> Thinking some more about it, perhaps the confusion would be sufficiently
>> reduced if the repr of '...' would be 'Ellipsis (...)', and use this repr
>> to appear in error messages rather than simply the name Ellipsis.
>>
>>
>>
>>>
>>> >
>>> > On Mon, 2021-05-31 at 11:37 -0300, André Roberge wrote:
>>> >> In Python `...` is referred to as `Ellipsis` and cannot be assigned
>>> to.
>>> >> Yet, one can assign any value to the name `Ellipsis`.
>>> >>
>>> >> Consider the following:
>>> >>
>>> >> ```
>>> >> >>> ...
>>> >> Ellipsis
>>> >> >>> ... == Ellipsis
>>> >> True
>>> >> >>> Ellipsis
>>> >> Ellipsis
>>> >> >>> Ellipsis = 3
>>> >> >>> Ellipsis
>>> >> 3
>>> >> >>> ... = 4
>>> >>   File "", line 1
>>> >> ... = 4
>>> >> ^
>>> >> SyntaxError: cannot assign to Ellipsis
>>> >> >>>  # But I just did assign a new value to the name Ellipsis above.
>>> >> >>> Ellipsis
>>> >> 3
>>> >> >>> ...
>>> >> Ellipsis
>>> >> >>> ... == Ellipsis
>>> >> False
>>> >> ```
>>> >>
>>> >> For consistency, `Ellipsis` (the name) should **always** refer to the
>>> >> same object that `...` refers to, so that both could not be assigned
>>> a
>>> >> new value.
>>> >>
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Guido van Rossum

Andre, did you have an experience where something related to Ellipsis/...
confused you? It is not clear to me what exactly prompted you to single out
Ellipsis (or it’s repr()?)

On Mon, May 31, 2021 at 08:37 André Roberge  wrote:

>
>
> On Mon, May 31, 2021 at 12:20 PM MRAB  wrote:
>
>> On 2021-05-31 15:55, Paul Bryan wrote:
>> > If you're proposing prevention of monkey patching Ellipsis, I think
>> > you'll have to go all-in on all builtins.
>> >
>> > For example:
>> >
>>  str = int
>> >
>>  str
>> >
>> > 
>> >
>>  str == int
>> >
>> > True
>> >
>> >
>> If you rebind str to int, the repr of str will say , so you
>> can tell that something's happened, but the repr of ... is always
>> 'Ellipsis', even though you've rebound Ellipsis.
>>
>
> Exactly.
>
> Thinking some more about it, perhaps the confusion would be sufficiently
> reduced if the repr of '...' would be 'Ellipsis (...)', and use this repr
> to appear in error messages rather than simply the name Ellipsis.
>
>
>
>>
>> >
>> > On Mon, 2021-05-31 at 11:37 -0300, André Roberge wrote:
>> >> In Python `...` is referred to as `Ellipsis` and cannot be assigned to.
>> >> Yet, one can assign any value to the name `Ellipsis`.
>> >>
>> >> Consider the following:
>> >>
>> >> ```
>> >> >>> ...
>> >> Ellipsis
>> >> >>> ... == Ellipsis
>> >> True
>> >> >>> Ellipsis
>> >> Ellipsis
>> >> >>> Ellipsis = 3
>> >> >>> Ellipsis
>> >> 3
>> >> >>> ... = 4
>> >>   File "", line 1
>> >> ... = 4
>> >> ^
>> >> SyntaxError: cannot assign to Ellipsis
>> >> >>>  # But I just did assign a new value to the name Ellipsis above.
>> >> >>> Ellipsis
>> >> 3
>> >> >>> ...
>> >> Ellipsis
>> >> >>> ... == Ellipsis
>> >> False
>> >> ```
>> >>
>> >> For consistency, `Ellipsis` (the name) should **always** refer to the
>> >> same object that `...` refers to, so that both could not be assigned a
>> >> new value.
>> >>
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread André Roberge

On Mon, May 31, 2021 at 12:20 PM MRAB  wrote:

> On 2021-05-31 15:55, Paul Bryan wrote:
> > If you're proposing prevention of monkey patching Ellipsis, I think
> > you'll have to go all-in on all builtins.
> >
> > For example:
> >
>  str = int
> >
>  str
> >
> > 
> >
>  str == int
> >
> > True
> >
> >
> If you rebind str to int, the repr of str will say , so you
> can tell that something's happened, but the repr of ... is always
> 'Ellipsis', even though you've rebound Ellipsis.
>

Exactly.

Thinking some more about it, perhaps the confusion would be sufficiently
reduced if the repr of '...' would be 'Ellipsis (...)', and use this repr
to appear in error messages rather than simply the name Ellipsis.



>
> >
> > On Mon, 2021-05-31 at 11:37 -0300, André Roberge wrote:
> >> In Python `...` is referred to as `Ellipsis` and cannot be assigned to.
> >> Yet, one can assign any value to the name `Ellipsis`.
> >>
> >> Consider the following:
> >>
> >> ```
> >> >>> ...
> >> Ellipsis
> >> >>> ... == Ellipsis
> >> True
> >> >>> Ellipsis
> >> Ellipsis
> >> >>> Ellipsis = 3
> >> >>> Ellipsis
> >> 3
> >> >>> ... = 4
> >>   File "", line 1
> >> ... = 4
> >> ^
> >> SyntaxError: cannot assign to Ellipsis
> >> >>>  # But I just did assign a new value to the name Ellipsis above.
> >> >>> Ellipsis
> >> 3
> >> >>> ...
> >> Ellipsis
> >> >>> ... == Ellipsis
> >> False
> >> ```
> >>
> >> For consistency, `Ellipsis` (the name) should **always** refer to the
> >> same object that `...` refers to, so that both could not be assigned a
> >> new value.
> >>
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[Python-ideas] Re: The name Ellipsis should be a constant

Fixing typo:

>>> s = str
>>> str = int
>>> str

>>> s


On Mon, 2021-05-31 at 08:31 -0700, Paul Bryan wrote:
> Because ... is still bound to the original Ellipsis. Just as "s"
> below will remain bound to the original str.
> 
> >>> s = str
> >>> str = int
> >>> int
> 
> >>> s
> 
> 
> Paul
> 
> On Mon, 2021-05-31 at 16:16 +0100, MRAB wrote:
> > On 2021-05-31 15:55, Paul Bryan wrote:
> > > If you're proposing prevention of monkey patching Ellipsis, I
> > > think 
> > > you'll have to go all-in on all builtins.
> > > 
> > > For example:
> > > 
> > > > > > str = int
> > > 
> > > > > > str
> > > 
> > > 
> > > 
> > > > > > str == int
> > > 
> > > True
> > > 
> > > 
> > If you rebind str to int, the repr of str will say ,
> > so you 
> > can tell that something's happened, but the repr of ... is always 
> > 'Ellipsis', even though you've rebound Ellipsis.
> > 
> > > 
> > > On Mon, 2021-05-31 at 11:37 -0300, André Roberge wrote:
> > > > In Python `...` is referred to as `Ellipsis` and cannot be
> > > > assigned to.
> > > > Yet, one can assign any value to the name `Ellipsis`.
> > > > 
> > > > Consider the following:
> > > > 
> > > > ```
> > > > > > > ...
> > > > Ellipsis
> > > > > > > ... == Ellipsis
> > > > True
> > > > > > > Ellipsis
> > > > Ellipsis
> > > > > > > Ellipsis = 3
> > > > > > > Ellipsis
> > > > 3
> > > > > > > ... = 4
> > > >   File "", line 1
> > > >     ... = 4
> > > >     ^
> > > > SyntaxError: cannot assign to Ellipsis
> > > > > > >   # But I just did assign a new value to the name
> > > > > > > Ellipsis above.
> > > > > > > Ellipsis
> > > > 3
> > > > > > > ...
> > > > Ellipsis
> > > > > > > ... == Ellipsis
> > > > False
> > > > ```
> > > > 
> > > > For consistency, `Ellipsis` (the name) should **always** refer
> > > > to the 
> > > > same object that `...` refers to, so that both could not be
> > > > assigned a 
> > > > new value.
> > > > 
> > ___
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[Python-ideas] Re: The name Ellipsis should be a constant

Because ... is still bound to the original Ellipsis. Just as "s" below
will remain bound to the original str.

>>> s = str
>>> str = int
>>> int

>>> s


Paul

On Mon, 2021-05-31 at 16:16 +0100, MRAB wrote:
> On 2021-05-31 15:55, Paul Bryan wrote:
> > If you're proposing prevention of monkey patching Ellipsis, I think
> > you'll have to go all-in on all builtins.
> > 
> > For example:
> > 
> > > > > str = int
> > 
> > > > > str
> > 
> > 
> > 
> > > > > str == int
> > 
> > True
> > 
> > 
> If you rebind str to int, the repr of str will say , so
> you 
> can tell that something's happened, but the repr of ... is always 
> 'Ellipsis', even though you've rebound Ellipsis.
> 
> > 
> > On Mon, 2021-05-31 at 11:37 -0300, André Roberge wrote:
> > > In Python `...` is referred to as `Ellipsis` and cannot be
> > > assigned to.
> > > Yet, one can assign any value to the name `Ellipsis`.
> > > 
> > > Consider the following:
> > > 
> > > ```
> > > > > > ...
> > > Ellipsis
> > > > > > ... == Ellipsis
> > > True
> > > > > > Ellipsis
> > > Ellipsis
> > > > > > Ellipsis = 3
> > > > > > Ellipsis
> > > 3
> > > > > > ... = 4
> > >   File "", line 1
> > >     ... = 4
> > >     ^
> > > SyntaxError: cannot assign to Ellipsis
> > > > > >   # But I just did assign a new value to the name Ellipsis
> > > > > > above.
> > > > > > Ellipsis
> > > 3
> > > > > > ...
> > > Ellipsis
> > > > > > ... == Ellipsis
> > > False
> > > ```
> > > 
> > > For consistency, `Ellipsis` (the name) should **always** refer to
> > > the 
> > > same object that `...` refers to, so that both could not be
> > > assigned a 
> > > new value.
> > > 
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread Simão Afonso

On 2021-05-31 16:16:59, MRAB wrote:
> If you rebind str to int, the repr of str will say , so you can
> tell that something's happened, but the repr of ... is always 'Ellipsis',
> even though you've rebound Ellipsis.

> >>> Ellipsis is ...
> True
> >>> Ellipsis = str
> >>> Ellipsis is ...
> False
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[Python-ideas] Re: The name Ellipsis should be a constant

2021-05-31 Thread MRAB

On 2021-05-31 15:55, Paul Bryan wrote:
If you're proposing prevention of monkey patching Ellipsis, I think 
you'll have to go all-in on all builtins.

For example:

str = int

str

str == int

True

If you rebind str to int, the repr of str will say , so you 
can tell that something's happened, but the repr of ... is always 
'Ellipsis', even though you've rebound Ellipsis.

On Mon, 2021-05-31 at 11:37 -0300, André Roberge wrote:

In Python `...` is referred to as `Ellipsis` and cannot be assigned to.
Yet, one can assign any value to the name `Ellipsis`.

Consider the following:

```
>>> ...
Ellipsis
>>> ... == Ellipsis
True
>>> Ellipsis
Ellipsis
>>> Ellipsis = 3
>>> Ellipsis
3
>>> ... = 4
  File "", line 1
    ... = 4
    ^
SyntaxError: cannot assign to Ellipsis
>>>  # But I just did assign a new value to the name Ellipsis above.
>>> Ellipsis
3
>>> ...
Ellipsis
>>> ... == Ellipsis
False
```

For consistency, `Ellipsis` (the name) should **always** refer to the 
same object that `...` refers to, so that both could not be assigned a 
new value.

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[Python-ideas] Re: The name Ellipsis should be a constant