[Python-Dev] PEP 572: Assignment Expressions (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Mon Apr 23 14:44:28 EDT 2018

On Mon, 23 Apr 2018 16:59:35 +0100 Steve Holden <steve at holdenweb.com> wrote:

On Mon, Apr 23, 2018 at 8:28 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:

> On Mon, 23 Apr 2018 00:44:44 -0500 > Tim Peters <tim.peters at gmail.com> wrote: > ​[...] > > > if (diff := x - xbase) and (g := gcd(diff, n)) > 1: > > return g > > That's so Pythonic I could cry ;-) > > ​[...] > > The second part, especially, where you use the result of an > assignment expression as a comparison operand, looks definitely > un-Pythonic. > ​Which, I suppose, underlines that Pythonicity is in the mind of the beholder.​

Indeed it is. What we can only say is that the proposed idiom goes against current Python syntactical rules :-)

The assignment expression seems like a vary natural way to introduce variables of limited (controlled?) scope, [...]

AFAIU, the scope isn't limited to the "if" block, it's a regular local variable. I might have misread.

While Tim's expression might look (superficially) like C, the five-line alternative isn't exactly an inspiring example of Pythonicity, is it?

I don't know. I've written my share of similar-looking code and I've never really been bothered, at least not enough that I thought we should change the language to accomodate those use cases. To be frank I don't remember the last time I was bothered by an aspect of Python's syntax. I think the language has reached "peak syntax" by now and it should basically be frozen, and any improvements targeted at other aspects (semantics, performance, stdlib, etc.).

Regardless, my three questions about this are:

My answer would be "no" to all three, but YMMV.

Regards

Antoine.

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