On 30 April 2018 at 17:37, Steven D'Aprano wrote:

On Mon, Apr 30, 2018 at 08:09:35AM +0100, Paddy McCarthy wrote: [...]

...

A PEP that can detract from readability; *readability*, a central tenet of Python, should be rejected, (on principle!), when such objections are treated so dismissively.

Unless you have an objective measurement of readability, that objection is mere subjective personal preference, and not one that everyone agrees with. I for one think that used wisely, binding expressions will be *more* readable than the alternatives. (Even though := is not my preferred syntax.)

On the other hand, the PEP doesn't do much to address the various claims of readability issues. Whether they are subjective or not, well-founded or not, the PEP does (in my view) come across as unnecessarily dismissive of the question of readability. I suspect that's largely due to Chris being extremely tired of having the same arguments over and over again, and I can understand that. However, I think it could be covered more completely - the remainder of your post is exactly the sort of response that would be useful to have recorded. But one way or another, I think people will vote on the PEP based on their (subjective) views, and so readability will get factored into the overall response, one way or another. To what extent that response affects Guido's final decision (I can't see him delegating on this one!) remains to be seen, and honestly, I'm willing to trust Guido's intuition. Paul

On 04/30/2018 12:37 PM, Steven D'Aprano wrote:

- comprehensions? not readable, easy to abuse, hard for beginners to comprehend;

I still refer to them as "list incomprehensions" in my head, particularly for those whic expand across line breaks. Tres. -- =================================================================== Tres Seaver +1 540-429-0999 tseaver@palladion.com Palladion Software "Excellence by Design" http://palladion.com

On Apr 30, 2018, at 9:37 AM, Steven D'Aprano wrote:

On Mon, Apr 30, 2018 at 08:09:35AM +0100, Paddy McCarthy wrote: [...]

...

A PEP that can detract from readability; *readability*, a central tenet of Python, should be rejected, (on principle!), when such objections are treated so dismissively.

Unless you have an objective measurement of readability, that objection is mere subjective personal preference, and not one that everyone agrees with.

Sorry Steven, but that doesn't seem like it is being fair to Paddy. Of course, readability can't be measured objectively with ruler (that is a false standard). However, readability is still a real issue that affects us daily even though objective measurement aren't possible. All of us who do code reviews make assessments of readability on a daily basis even though we have no objective measures. We know hard to read when we see it. In this thread, several prominent and highly experienced devs reported finding it difficult to parse some of the examples and some mis-parsed the semantics of the examples. It is an objective fact that they reported readability issues. That is of great concern and shouldn't be blown off with a comment that readability, "is a mere subjective personal preference". At its heart, readability is the number one concern in language design. Also, there another area where it looks like valid concerns are being dismissed out of hand. Several respondents worried that the proposed feature will lead to writing bad code. Their comments seem to have been swept under the table with responses along the lines of "well any feature can be used badly, so we don't care about that, some people will write bad code no matter what we do". While that is true to some extent, there remains a valid issue concerning the propensity for misuse. ISTM the proposed feature relies on users showing a good deal of self-restriaint and having a clear knowledge of boundary between the "clear-win" cases (like the regex match object example) and the puzzling cases (assignments being used in and-operator and or-operator chains). It also relies on people not making hard to find mistakes (like mistyping := when == was intended). There is a real difference between a feature that could be abused versus a feature that has a propensity for being misused, being mistyped, or being misread (all of which have occurred multiple times in these threads).

The "not readable" objection has been made, extremely vehemently, against nearly all major syntax changes to Python:

I think that is a false recollection of history. Comprehensions were welcomed and highly desired. Decorators were also highly sought after -- there was only a question of the best possible syntax. The ternary operator was clamored for by an enormous number of users (though there was little agreement on the best spelling). Likewise, the case for augmented assignments was somewhat strong (eliminating having to spell the assignment target twice). Each of those proposals had their debates, but none of them had a bunch of core devs flat-out opposed like we do now. It really isn't the same at all. However, even if the history had been recalled correctly, it would still be a logical fallacy to posit "in the past, people opposed syntax changes that later proved to be popular, therefore we should ignore all concerns being expressed today". To me, that seems like a rhetorical trick for dismissing a bunch of thoughtful posts. Adding this new syntax is a one-way trip -- we don't get to express regrets later. Accordingly, it would be nice if the various concerns being presented were addressed directly rather than being dismissed with a turn of phrase. Nor should it matter whether concerns were articulately expressed (being articulate isn't always correlated with being right). Raymond