[Python-Dev] assignment expressions: an alternative proposal

[Paul Moore]

On 24 April 2018 at 15:58, Yury Selivanov <yselivanov.ml at gmail.com> wrote:
> On Tue, Apr 24, 2018 at 10:49 AM, Paul Moore <p.f.moore at gmail.com> wrote:
> [..]
>>>> 3. Most importantly: it is *not* allowed to mask names in the current
>>>> local scope.
>>>
>>> While I agree this would be unambiguous to a computer, I think for
>>> most humans it would be experienced as a confusing set of arcane and
>>> arbitrary rules about what "=" means in Python.
>>
>> Also, there's the ambiguity and potential for misreading in the
>> opposite direction (accidentally *reading* = as == even though it
>> isn't):
>>
>> if (diff = x - x_base) and (g = gcd(diff, n)) > 1:
>>      return g
>
> Since 'diff' and 'g' must be new names according to rule (3), those
> who read the code will notice that both were not previously bound.
> Therefore both are new variables so it can't be a comparison.

That was essentially my point, though - I can no longer read that line
of code in isolation from the surrounding context. Consider something
like a github PR review screen, where surrounding unchanged code is
frequently hidden.

Anyway, we can agree to differ on this - I don't like this idea and
I'd personally find it hard to read, but as you've already pointed
out, this is all extremely subjective.
Paul