Re: [Python-ideas] Null coalescing operator

On Thu, Nov 3, 2016 at 4:06 PM, Steven D'Aprano wrote: > > > No, ?? is a bit like 'or', except that only None is falsey, so it > would be: > > > > > > self.an_arg = an_arg ?? the_default > > > > > > thanks! and actually, that reads much better to me. > > That suggests a

Re: [Python-ideas] Null coalescing operator

On Thu, Nov 03, 2016 at 12:35:07PM -0700, Chris Barker wrote: > On Thu, Nov 3, 2016 at 12:00 PM, MRAB wrote: > > > self.an_arg = the_default if an_arg is None else an_arg > > > No, ?? is a bit like 'or', except that only None is falsey, so it would be: > > > >

Re: [Python-ideas] Null coalescing operator

On Thu, Nov 3, 2016 at 12:00 PM, MRAB wrote: > self.an_arg = the_default if an_arg is None else an_arg > > > No, ?? is a bit like 'or', except that only None is falsey, so it would be: >> > > self.an_arg = an_arg ?? the_default thanks! and actually, that reads

Re: [Python-ideas] Null coalescing operator

On 2016-11-03 18:36, Chris Barker wrote: Thanks Steven, this is great! so -- when all this started, I think one of the use cases was to clean up this really common idiom: self.an_arg = the_default if an_arg is None else an_arg so would that be: self.an_arg = the_default ?? an_arg That would

Re: [Python-ideas] Null coalescing operator

Thanks Steven, this is great! so -- when all this started, I think one of the use cases was to clean up this really common idiom: self.an_arg = the_default if an_arg is None else an_arg so would that be: self.an_arg = the_default ?? an_arg That would be nice. Though the fact that I'm still

Re: [Python-ideas] Null coalescing operator

Steven D'Aprano wrote: Or even the subject line of this email thread??? Sorry, crossed over discussions. But I think it's also true that the null-coalescing idea is for cases where it's not an error for something to be None. -- Greg ___

Re: [Python-ideas] Null coalescing operator

On 11/2/2016 2:30 PM, Zero Piraeus wrote: If I write something like obj.attr, the failure mode I care about is that obj has no attribute attr, rather than that obj is specifically None (or one of a defined group of somewhat Nonelike objects). I agree with this understanding. The problem

Re: [Python-ideas] Null coalescing operator

On Thu, Nov 03, 2016 at 11:22:45AM +1300, Greg Ewing wrote: > The proposed .? syntax is designed for cases where it's *not* > an error for the object to be missing the attribute, No it is not. That is absolutely not what the syntax means. I'm sorry to single you out Greg, but have you read the

Re: [Python-ideas] Null coalescing operator

On 2016-11-02 21:57, Greg Ewing wrote: MRAB wrote: target = expr1 || expr2 || expr3 target = expr1 && expr2 && expr3 except that only None would be considered falsey? Or would that be confusing? Yes, I think that borrowing an operator from C but giving it subtly different semantics

Re: [Python-ideas] Null coalescing operator

On Thu, Nov 03, 2016 at 02:17:14AM +1000, Nick Coghlan wrote: > Yeah, and so far the protocol based alternative I'm working on hasn't > been any less headache-inducing (Mark has been reviewing some early > iterations and had to draw a diagram to try to follow the proposed > control flow). Even

Re: [Python-ideas] Null coalescing operator

On 2 November 2016 at 21:50, David Mertz wrote: > Even though I really don't want new null-coalescing operators, I really > appreciate the ternary operator in Python (or in C). > > On Wed, Nov 2, 2016 at 12:38 PM, Mikhail V wrote: >> >> result = a > b ? x :

Re: [Python-ideas] Null coalescing operator

On Wed, Nov 02, 2016 at 08:46:54AM -0700, Guido van Rossum wrote: > But first we need to agree on what even the right definition > of ?. is. It's been frighteningly difficult to explain this even on this > list, even though I have a very clear view in my head, This is Python-Ideas and with

Re: [Python-ideas] Null coalescing operator

On 10/31/16, Guido van Rossum wrote: > For "everything to the right" it would seem we have some freedom: e.g. if > we have "foo.bar?.baz(bletch)" is the call included? The answer is yes -- > the concept we're after here is named "trailer" in the Grammar file in the > source

Re: [Python-ideas] Null coalescing operator

I actually think that Zero's point here is quite valid... At some earlier point in the thread, I believe that Nick Coughlin was saying that we should be asking ourselves _why_ we want to do something like this and the result of that discussion was because there is pain when working with

Re: [Python-ideas] Null coalescing operator

On 10/15/16, Nick Coghlan wrote: > * None-coalescing operator: x ?or y > * None-severing operator: x ?and y > * None-coalescing augmented assignment: x ?= y > * None-severing attribute access: x?.attr > * None-severing subscript lookup: x?[expr] Please don't be too harsh to

Re: [Python-ideas] Null coalescing operator

Zero Piraeus writes: If I write something like obj.attr, the failure mode I care about is that obj has no attribute attr, rather than that obj is specifically None (or one of a defined group of somewhat Nonelike objects). Clearly, in such a circumstance, obj is not what I

Re: [Python-ideas] Null coalescing operator

Even though I really don't want new null-coalescing operators, I really appreciate the ternary operator in Python (or in C). On Wed, Nov 2, 2016 at 12:38 PM, Mikhail V wrote: > result = a > b ? x : y > > is IMHO a syntactical herecy. Such things disgust me from

Re: [Python-ideas] Null coalescing operator

Zero Piraeus writes: > If I write something like obj.attr, the failure mode I care about is that > obj has no attribute attr, rather than that obj is specifically None (or > one of a defined group of somewhat Nonelike objects). > > Clearly, in such a circumstance, obj is not what I expected it to

Re: [Python-ideas] Null coalescing operator

On 11/02/2016 12:32 PM, Nikolaus Rath wrote: On Nov 02 2016, Zero Piraeus wrote: On Wed, 2016-11-02 at 08:46 -0700, Guido van Rossum wrote: [...] we need to agree on what even the right definition of ?. is. It's been frighteningly difficult to

Re: [Python-ideas] Null coalescing operator

On Nov 02 2016, Zero Piraeus wrote: > On Wed, 2016-11-02 at 08:46 -0700, Guido van Rossum wrote: >> [...] we need to agree on what even the right definition of ?. is. It's >> been frighteningly difficult to explain this even on this list, even >>

Re: [Python-ideas] Null coalescing operator

On 2 November 2016 at 19:34, MRAB wrote: > How about borrowing from C: > > target = expr1 || expr2 || expr3 > target = expr1 && expr2 && expr3 > > except that only None would be considered falsey? > > Or would that be confusing? Sorry for intruding into

Re: [Python-ideas] Null coalescing operator

On 2016-11-02 16:17, Nick Coghlan wrote: [snip] Yeah, and so far the protocol based alternative I'm working on hasn't been any less headache-inducing (Mark has been reviewing some early iterations and had to draw a diagram to try to follow the proposed control flow). I think I have a way to

Re: [Python-ideas] Null coalescing operator

: Disclaimer: I haven't followed all of this discussion, so some or all of the following may already have been expressed better (and perhaps refuted better still). On Wed, 2016-11-02 at 08:46 -0700, Guido van Rossum wrote: > [...] we need to agree on what even the right definition of ?. is. It's

Re: [Python-ideas] Null coalescing operator

On 02.11.2016 17:17, Nick Coghlan wrote: The gist is that rather than writing the bare: target = expr1 ?? expr2 ?? expr3 You'd instead write None-coalescing as: target = exists(expr1) ?? exists(expr2) ?? expr3 and None-propagating as: target = missing(expr1) ?? missing(expr2) ??

Re: [Python-ideas] Null coalescing operator

On 3 November 2016 at 01:46, Guido van Rossum wrote: > But I also recall learning CoffeeScript via cargo-culting a large existing > codebase and having not the foggiest ideas when it made sense to use ?. and > when plain . was enough. So I think this feature is not very >

Re: [Python-ideas] Null coalescing operator

On 2 November 2016 at 00:46, Guido van Rossum wrote: > I personally find the ?keyword pattern has less appeal than ?, ?? or ?. . Good to know :) Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia ___

Re: [Python-ideas] Null coalescing operator

On Wed, Nov 2, 2016 at 9:18 PM, Steven D'Aprano wrote: > On Wed, Nov 02, 2016 at 02:09:24PM +1100, Chris Angelico wrote: >> We already expect "to the left" and "to the right" to end based on >> operator precedence rules. Parentheses are used to control operator >> precedence.

Re: [Python-ideas] Null coalescing operator

Geez. --Guido (mobile) On Nov 1, 2016 8:10 PM, "Chris Angelico" wrote: > On Wed, Nov 2, 2016 at 11:09 AM, Steven D'Aprano > wrote: > > I don't know when I would ever want to actually do this in practice, but > > allowing the ?. operator to magically

Re: [Python-ideas] Null coalescing operator

On Mon, Oct 31, 2016 at 05:44:07PM -0400, Random832 wrote: > Right now, foo.bar.baz(bletch) is Call(Attribute(Attribute(Name('foo'), > 'bar'), 'baz'), [Name('bletch')])), which is identical to > (foo.bar).baz(bletch) or (foo.bar.baz)(bletch). These are treated, > essentially, as postfix

Re: [Python-ideas] Null coalescing operator

I personally find the ?keyword pattern has less appeal than ?, ?? or ?. . On Tue, Nov 1, 2016 at 4:02 AM, Nick Coghlan wrote: > On 1 November 2016 at 20:28, Paul Moore wrote: > > On 1 November 2016 at 10:11, Nick Coghlan wrote: > >>

Re: [Python-ideas] Null coalescing operator

On 1 November 2016 at 20:28, Paul Moore wrote: > On 1 November 2016 at 10:11, Nick Coghlan wrote: >> >> I do think it would be worth covering the symbol+keyword option >> discussed in PEP 531 (i.e. "?else" instead of "??", but keeping "?.", >> and "?[") >

Re: [Python-ideas] Null coalescing operator

On 1 November 2016 at 10:11, Nick Coghlan wrote: > > I do think it would be worth covering the symbol+keyword option > discussed in PEP 531 (i.e. "?else" instead of "??", but keeping "?.", > and "?[") FWIW, I'm not keen on it. As a technical question, would it be treated in

Re: [Python-ideas] Null coalescing operator

Obviously the AST needs to be changed. How? I dunno. Sounds like you have some ideas. :-) On Mon, Oct 31, 2016 at 2:44 PM, Random832 wrote: > On Mon, Oct 31, 2016, at 13:16, Guido van Rossum wrote: > > For "everything to the right" it would seem we have some freedom:

Re: [Python-ideas] Null coalescing operator

On Mon, Oct 31, 2016, at 13:16, Guido van Rossum wrote: > For "everything to the right" it would seem we have some freedom: e.g. > if we have "foo.bar?.baz(bletch)" is the call included? The answer is > yes -- the concept we're after here is named "trailer" in the Grammar > file in the source code

Re: [Python-ideas] Null coalescing operator

On 2016-10-31 17:16, Guido van Rossum wrote: I think we should try to improve our intutition about these operators. Many things that are intuitively clear still require long turgid paragraphs in reference documentation to state the behavior unambiguously -- but that doesn't stop us from

Re: [Python-ideas] Null coalescing operator

On 31 October 2016 at 17:16, Guido van Rossum wrote: > I think we should try to improve our intutition about these operators. Many > things that are intuitively clear still require long turgid paragraphs in > reference documentation to state the behavior unambiguously -- but

Re: [Python-ideas] Null coalescing operator

I think we should try to improve our intutition about these operators. Many things that are intuitively clear still require long turgid paragraphs in reference documentation to state the behavior unambiguously -- but that doesn't stop us from intuitively grasping concepts like a+b (when does

Re: [Python-ideas] Null coalescing operator

The PEP combines ideas from several different languages. For example: * Both Dart and C# have "x ?? y" and "x?.y". * Dart has "x ??= y" and C# does not. * C# has short circuit semantics for "?." and Dart does not. * PHP has "??" but does not have "?." * Etc. Wikipedia lists a lot of other

Re: [Python-ideas] Null coalescing operator

Stephen J. Turnbull wrote: > I gather you think you have a deadlock here. The way to break it is > to just do it. Pick a syntax and do the rewriting. My memory of some > past instances is that many of the senior devs (especially Guido) will > "see through the syntax" to evaluate the benefits

Re: [Python-ideas] Null coalescing operator

On 29 October 2016 at 18:19, Stephen J. Turnbull wrote: >> For better or worse, it may be emoji that drive that change ;-) >> >> I suspect that the 100 million or so Chinese, Japanese, Korean, and >> Indian programmers who have had systems that have no trouble >> whatsoever handling non-ASCII for

Re: [Python-ideas] Null coalescing operator

On 29 October 2016 at 18:19, Stephen J. Turnbull wrote: >> For better or worse, it may be emoji that drive that change ;-) > > I suspect that the 100 million or so Chinese, Japanese, Korean, and > Indian programmers who have had systems that have no trouble >

Re: [Python-ideas] Null coalescing operator

Steven d'Aprano writes: > I think you mean WHITE SQUARE? At least, I can not see any "OPEN > SQUARE" code point in Unicode, and the character you use below □ > is called WHITE SQUARE. You're right, I just used a common Japanese name for it. I even checked the table to make sure it was BMP

Re: [Python-ideas] Null coalescing operator

On Sat, Oct 29, 2016 at 11:02:36AM +0900, Stephen J. Turnbull wrote: > Unfortunately here the most plausible syntax is one > that Guido has said he definitely doesn't like: using '?'. The > alternatives are pretty horrible (a Haskell-like 'maybe' keyword, or > the OPEN SQUARE character used by

Re: [Python-ideas] Null coalescing operator

Mark E. Haase writes: > In terms of "bunch of longer examples", what did you have in mind? > I could take some popular library and rewrite a section of it with > the proposed operators, but that would depend on the response to > the previous paragraph. I gather you think you have a deadlock

Re: [Python-ideas] Null coalescing operator

On Oct 28, 2016, at 03:24 PM, Gustavo Carneiro wrote: >The main drawback of this type of approach is that code checking tools will >hardly ever support checking expressions inside the string like that. >Also, you don't get proper syntax highlighting, code completion, etc. > >You can do anything

Re: [Python-ideas] Null coalescing operator

On 28 October 2016 at 14:13, Barry Warsaw wrote: > On Oct 27, 2016, at 07:37 PM, Nick Badger wrote: > > >The problem with doing that is that it's ambiguous. There's no way of > >telling which attribute is allowed to coalesce. > > You could of course support exactly the same

Re: [Python-ideas] Null coalescing operator

On Fri, Oct 28, 2016 at 7:13 AM, Barry Warsaw wrote: > You could of course support exactly the same syntax being proposed as a > language change, e.g. > > from operator import attrgetter > r = attrgetter('b?.x?.z') > > and then you wouldn't even need the `coalesce`

Re: [Python-ideas] Null coalescing operator

On Oct 27, 2016, at 07:37 PM, Nick Badger wrote: >The problem with doing that is that it's ambiguous. There's no way of >telling which attribute is allowed to coalesce. You could of course support exactly the same syntax being proposed as a language change, e.g. from operator import

Re: [Python-ideas] Null coalescing operator

The problem with doing that is that it's ambiguous. There's no way of telling which attribute is allowed to coalesce. I think one of the best arguments for a coalescing operator in Python is that it allows you to be more explicit, without the hassle of nested try: except AttributeError blocks.

Re: [Python-ideas] Null coalescing operator

On Thu, Oct 27, 2016, at 11:27, Joonas Liik wrote: > perhaps just having a utility function can get us some of the way there.. > > #may error > r = a.b.x.z > > # will default to None > r = a?.b?.x?.z If a.b can't or shouldn't be None, this should be a?.b.x.z I'm not certain how your utility

Re: [Python-ideas] Null coalescing operator

perhaps just having a utility function can get us some of the way there.. #may error r = a.b.x.z # will default to None r = a?.b?.x?.z r = get_null_aware(a, "b.x.z") # long but no new syntax, can be implemented today. ___ Python-ideas mailing list

Re: [Python-ideas] Null coalescing operator

On 15 October 2016 at 13:36, Guido van Rossum wrote: > I'm not usually swayed by surveys -- Python is not a democracy. Maybe > a bunch of longer examples would help all of us see the advantages of > the proposals. Having been previously somewhere between -1 and -0, I've been

Re: [Python-ideas] Null coalescing operator

I'm not usually swayed by surveys -- Python is not a democracy. Maybe a bunch of longer examples would help all of us see the advantages of the proposals. On Fri, Oct 14, 2016 at 8:09 PM, Mark E. Haase wrote: > On Fri, Oct 14, 2016 at 12:10 PM, Guido van Rossum

Re: [Python-ideas] Null coalescing operator

On Fri, Oct 14, 2016 at 12:10 PM, Guido van Rossum wrote: > I propose that the next phase of the process should be to pick the > best operator for each sub-proposal. Then we can decide which of the > sub-proposals we actually want in the language, based on a combination > of

Re: [Python-ideas] Null coalescing operator

For what it's worth, I like the C# syntax with question marks. It is probably more risky (breaks more code) to introduce a new keyword than a new symbol as operator. If we have to pick a symbol, it's less confusing if we pick something another language already uses. There is no shame in copying

Re: [Python-ideas] Null coalescing operator

I actually think the spelling is the main stumbling block. The intrinsic value of the behavior is clear, it's finding an acceptable spelling that hold back the proposal. I propose that the next phase of the process should be to pick the best operator for each sub-proposal. Then we can decide

Re: [Python-ideas] Null coalescing operator

On Sat, Sep 10, 2016 at 4:27 PM, Chris Angelico wrote: > On Sun, Sep 11, 2016 at 9:10 AM, Guido van Rossum wrote: >> So you're offering `NoneCoalesce(x).bar` as less-ugly alternative to >> `x?.bar`... Color me unconvinced. > > As a syntactic form? Not

Re: [Python-ideas] Null coalescing operator

So you're offering `NoneCoalesce(x).bar` as less-ugly alternative to `x?.bar`... Color me unconvinced. On Sat, Sep 10, 2016 at 4:06 PM, David Mertz wrote: > Actually, I guess the example I liked was from the year ago discussion. And > it didn't do *exactly* what I think a

Re: [Python-ideas] Null coalescing operator

https://github.com/kirbyfan64/_frozensafemockobjectimplementation In all seriousness, though, I really feel like that would be the ultimate bug magnet, since it'd be easy to forget to un-wrap the object afterwards. -- Ryan [ERROR]: Your autotools build scripts are 200 lines longer than your

Re: [Python-ideas] Null coalescing operator

I find the '?.' syntax very ugly, much more so in the examples of chained attributes. A much better way to handle the use case is to wrap objects in a class that gives this "propagating None" behavior with plain attribute access. A nice implementation was presented in this thread. On Sep 10,

Re: [Python-ideas] Null coalescing operator

On Sat, Sep 10, 2016, at 13:26, Guido van Rossum wrote: > The way I recall it, we arrived at the perfect syntax (using ?) and > semantics. The issue was purely strong hesitation about whether > sprinkling ? all over your code is too ugly for Python I think that if there's "strong hesitation"

Re: [Python-ideas] Null coalescing operator

On Sat, Sep 10, 2016 at 4:56 PM, Guido van Rossum wrote: > Another issue already discussed in PEP 505 is a conflict with IPython > (Jupyter Notebook), which uses ? and ?? as custom syntax to request > help. But maybe it can be taught to only recognize those when they're > the

Re: [Python-ideas] Null coalescing operator

On Sat, Sep 10, 2016 at 11:09 AM, MRAB wrote: > On 2016-09-10 18:44, Paul Moore wrote: >> >> On 10 September 2016 at 18:26, Guido van Rossum wrote: >>> >>> IMO the key syntax is >>> simply one for accessing attributes returning None instead of

Re: [Python-ideas] Null coalescing operator

On 10 September 2016 at 18:26, Guido van Rossum wrote: > IMO the key syntax is > simply one for accessing attributes returning None instead of raising > AttributeError, so that e.g. `foo?.bar?.baz` is roughly equivalent to > `foo.bar.baz if (foo is not None and foo.bar is not

Re: [Python-ideas] Null coalescing operator

On 10.09.2016 19:14, Random832 wrote: As I remember the discussion, I thought he'd more or less conceded on the use of ? but there was disagreement on how to implement it that never got resolved. Concerns like, you can't have a?.b return None because then a?.b() isn't callable, unless you want

Re: [Python-ideas] Null coalescing operator

It is PEP 505. I agree we should resume the discussion on this PEP though (for 3.7), I'm not completely sure why it stalled. Ralph On Sat, 10 Sep 2016, 02:50 Steven D'Aprano, wrote: > On Fri, Sep 09, 2016 at 10:01:44PM +0200, Arek Bulski wrote: > > Sometimes I find myself

Re: [Python-ideas] Null coalescing operator

On Fri, Sep 09, 2016 at 10:01:44PM +0200, Arek Bulski wrote: > Sometimes I find myself in need of this nice operator that I used back in > the days when I was programming in .NET, essentially an expression > > >>> expr ?? instead > > should return expr when it `is not None` and `instead`

Re: [Python-ideas] Null coalescing operator

On 2016-09-09 21:01, Arek Bulski wrote: Sometimes I find myself in need of this nice operator that I used back in the days when I was programming in .NET, essentially an expression expr ?? instead should return expr when it `is not None` and `instead` otherwise. A piece of code that I just

Re: [Python-ideas] Null coalescing operator

I'd note you can also save 4 characters by writing: instead if expr is None else expr On Fri, Sep 9, 2016 at 1:10 PM, David Mertz wrote: > This idea has come up before. While I can see the use of it, to me at > least that use doesn't feel nearly common enough to warrant

Re: [Python-ideas] Null coalescing operator

This idea has come up before. While I can see the use of it, to me at least that use doesn't feel nearly common enough to warrant dedicated syntax. In many cases, it is a "truthy" value you are looking for rather than `is not None` specifically. That has a convenient spelling: expr or instead

Re: [Python-ideas] Null coalescing operator

On Sat, Sep 10, 2016 at 6:01 AM, Arek Bulski wrote: > Sometimes I find myself in need of this nice operator that I used back in > the days when I was programming in .NET, essentially an expression > expr ?? instead > > should return expr when it `is not None` and