[Python-ideas] PEP 505: None-aware operators

[Chris Angelico]

On Wed, Aug 1, 2018 at 7:09 PM, Jonathan Fine <jfine2358 at gmail.com> wrote:
> Hi Chris
>
> We're discussing.
>> 10) a ?. b ?. c
>> 11) (a ?. b) ?. c
>
> I asked
>> So, are there any values of 'a' for which #10 and #11 don't give the
>> same result?
>
> You replied
>> I'm not prepared to put my neck out and say "They are absolutely
>> identical" and have people jump on me with some technicality. What is
>> your point here?
>
> I am willing to put my neck out and say a.b.c and (a.b).c are
> equivalent. And my understanding for PEP 505 is that #10 and #11 is
> that they are equivalent.

The first pair are easily proven, since we can just probe existing code.

>>> import dis
>>> dis.dis(lambda a: a.b.c)
  1           0 LOAD_FAST                0 (a)
              2 LOAD_ATTR                0 (b)
              4 LOAD_ATTR                1 (c)
              6 RETURN_VALUE
>>> dis.dis(lambda a: (a.b).c)
  1           0 LOAD_FAST                0 (a)
              2 LOAD_ATTR                0 (b)
              4 LOAD_ATTR                1 (c)
              6 RETURN_VALUE
>>>

Same byte code? Same result. Unless there's a bug in the peephole
optimizer or something, which I doubt.

ChrisA