[Python-Dev] Examples for PEP 572 (original) (raw)

Tim Peters tim.peters at gmail.com
Wed Jul 4 13:58:39 EDT 2018

[Serhiy Storchaka]

> Sorry, this PEP was rewritten so many times that I missed your [Tim's] Appendix.

>

>> while total != (total := total + term):

>> term = mx2 / (i(i+1))

>> i += 2

>> return total

>

> This code looks clever that the original while loop with a break in a

> middle. I like clever code. But it needs more mental efforts for

> understanding it.

>

> I admit that this is a good example.

>

> There is a tiny problem with it (and with rewriting a while loop as a

> for loop, as I like). Often the body contains not a single break. In

> this case the large part of cleverness is disappeared. :-(

[Ivan Pozdeev]

It took me a few minutes to figure out that this construct actually

> checks term == 0.

>

> So, this example abuses the construct to do something it's not designed

> to do: perform an unrelated operation before checking the condition.

> (Cue attempts to squeeze ever mode code here.) I would fail it in review.

>

> This "clever" code is exactly what Perl burned itself on and what

> Python, being its antithesis, was specifically designed to avoid.

So you didn't read the PEP Appendix at all, and Serhiy did but apparently skipped reading what the PEP said about that example. It was clearly identified as abuse: a case in which using assignment expressions made the code significantly WORSE. I gave examples of both "wins" and "losses" while staring at real code - I wasn't searching for "proof" that a pre-determined conclusion was justified.

So I wholly agree with you (Ivan) about that example - and that it struck Serhiy as a good example convinces me more than before that there's no overlap in the ways Serhiy and I view this part of the world ;-) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20180704/84b9ca8c/attachment.html>

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