I think I am with Michael here. I like the parallel between `??` and `or`, we don't have `or=`, so `??=` is also not needed. Although I understand a parallel between `obj.attr` and `obj['attr']`, I think there is an additional point (in addition to two valid points by Michael) why I don't like `?[`: in many situations in my experience optional container attributes were results of suboptimal APIs, so I would not encourage this pattern. FWIW, I am rather -0 on adding all proposed operators, but I would be +1 on adding just the two essential ones: ?? and ?. -- Ivan On 20 July 2018 at 01:40, Michael Lee <michael.lee.0x2a@gmail.com> wrote:
Hi -- I'm a new voice here, though I've been lurking for a while now.
How do people feel about removing "??=" and "foo?[bar]" from the PEP and sticking with just "foo?.bar" and "foo ?? bar"?
Reasons for not implementing "??=":
1. I think the other operators are useful in that they can be chained together to shrink many different lines of code. In contrast, ??= can shrink at most one line of code: we get to remove a single 'if foo is None'. If the rest of the PEP is implemented, we can also just express this by doing "foo = foo ?? some_expr" which I think is still relatively concise.
2. None of the other short-circuiting operators have an augmented assignment form -- e.g. we can do "foo = foo or bar", but there's no such thing as "foo or= bar". I don't really see why ?? in particular deserves to have an augmented assignment form.
3. We already have two different kinds of assignment operators with the inclusion of PEP 572 -- in the interests of keeping Python as simple as possible, I think it'd be a good idea not to add a third one.
Reasons for not implementing "foo?[bar]":
1. It seems like "foo?[bar]" could be easily confused with "foo??[bar]". I don't think it's immediately obvious to a newcomer which spelling corresponds to which usage, and getting the two mixed up seems like the sort of thing that could cause all sorts of subtle bugs.
2. We can already easily get the same functionality using standard Python. E.g., instead of doing foo?["bar"]?[0]?["baz"], we could do lookup(foo, "bar", 0, "baz") where lookup is a function that looks roughly like this:
def lookup(item, *parts): for part in parts: if item is None: return None item = item[parts] return item
Of course, we could probably create the same sort of function to replace foo?.bar (albeit less ergonomically), but unlike foo?[bar], there's no possibility for confusion: doing foo??.bar will never be a valid Python expression.
3. One counter-argument against removing foo?[bar] is that it would make expression that need both safe index and attribute lookups look weird -- you'd sometimes be using the "lookup" function described above (or something similar) and sometimes using ".?". However, I'd argue that these sorts of scenarios are relatively rare in practice, and that if you really need to deal with a bunch of code that requires you to use both forms of safe navigation, your code is likely already becoming pretty unreadable and should be rewritten -- maybe split up into multiple lines or something, or maybe just redesigned from scratch so you don't need to constantly manage a mess of Nones.
More broadly, I think I agree with the sentiment some other people have that Python has acquired a lot of new features in a relatively short period of time, and that it would be nice to have some cooldown to let tooling and other implementations catch up. In that regard, I'd personally be happy if we didn't implement this PEP or just deferred it again. But if we *are* moving forward with it, I think it's worth trying to simplify it as much as possible/try and make it orthogonal with existing Python features.
(But of course, I'm just some random person on the internet, so IDK if my opinion counts for much.)
Regards, -- Michael
On Thu, Jul 19, 2018 at 5:06 PM, Chris Angelico <rosuav@gmail.com> wrote:
On Fri, Jul 20, 2018 at 10:03 AM, Greg Ewing <greg.ewing@canterbury.ac.nz> wrote:
Rhodri James wrote:
If anyone can think of a good word for "if it isn't None, otherwise",
I'd
be all for it :-)
I don't think there's any single Engish word that captures all of that, so we'd have to invent one.
Some suggestions:
inno (If Not None, Otherwise)
oft (Or, Failing That)
Iunno, that'd oft be confusing.
Kappa
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