[Python-Dev] PEP 572: Assignment Expressions

[Chris Angelico]

On Tue, Apr 24, 2018 at 6:21 AM, Sven R. Kunze <srkunze at mail.de> wrote:
> On 23.04.2018 19:24, Chris Angelico wrote:
>>
>> On Tue, Apr 24, 2018 at 3:13 AM, Sven R. Kunze <srkunze at mail.de> wrote:
>>>
>>> diff = x - x_base
>>> if diff and gcd(diff, n) > 1:
>>>      return gcd(diff, n)
>>>
>>> # or
>>>
>>> if (x - x_base) and gcd(x - x_base, n) > 1:
>>>      return gcd(x - x_base, n)
>>>
>>>
>>> and have the interpreter handle the optimization, or apply an lru_cache?
>>> ;-)
>>
>> And then you want to change something, and you have to make an edit in
>> two places. Or, worse, you make it in only one of those places, they
>> become desynchronized, and nobody can figure out why the program
>> occasionally and bizarrely fails.
>
>
> If you change any of those lines (including ones of my fore-posters) without
> knowing what you're doing, you'd better don't touch them at all.
>
> The SQL folks btw. are pretty okay'ish with this kind of duplication because
> they can resolve it. Surely, Python isn't SQL but sometimes I wish Python
> could handle such things as easily without me having to babysit it all the
> time and using Perl'ish syntax (which := looks like to me). We then have :=,
> = and ==. Sorry, but Python wouldn't fit my brain then.
>

Ah, are you one of those programmers who writes code once and it's
instantly perfect? I apologize, I didn't realize I was in the presence
of a unicorn.

Most programmers will end up making edits to all non-trivial code. And
if your code is laid out in such a way that edits are easier and
safer, you're less likely to introduce bugs as you edit. Duplication
works against that by forcing you to make changes in two places.

I've seen code that relies on duplication and compiler optimizations.
Sure, it'll run just as fast as the equivalent with actual variable
names; but that's beside the point. It takes extra effort to maintain
such code, and that is what matters.

ChrisA