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

[Grégory Lielens]

On Monday, July 23, 2018 at 8:24:45 AM UTC+2, Nicholas Cole wrote:

And that leads to a simple question: how many times does this actually 
> occur in real-world by python code? -- i.e. how many times do I want 
> to check the value of an existing label, and, finding it is None (and 
> None specifically), then assign it a value? 
>

The PEP present a few examples.

I think the compactness and clarity is really gained when doing a descent 
into an "attribute tree", where any (or selected) members can be None, like 
getting back to the  example by Steven (spell-corrected, and expanded):

 meal = obj?.spam?.eggs.tomato?.cheese ?? "Mozzarella"

Where, to put the proposal in even better light, I have assumed that eggs 
instances always have a tomato attributes (i.e. are never None).

This is indeed much more compact that the current version, and arguably 
more readable (it's easier to parse once you know the syntax...but you have 
to know the special syntax that will be used for this kind of stuff only). 
The more you deepen the attribute access, the more you gain, but of course 
deep attribute access is not so common. The new operators may make deep 
attribute hierarchies (or deeply nested dicts/lists) slightly more common, 
and there also I do not think it's a good thing.

For me the issue is that you gain little, each operator is very limited in 
scope, but at the same it's a operator, and those are introduced very 
carefully in Python (the resistance to line noise is high, it's one of the 
defining aspect of Python since forever).

Each of them do not do enough IMHO, it's too special case and do not unlock 
especially powerfull/elegant/generalization reuse of other part of Python 
syntax. If you add something, it should play nice with the existing feature 
and solve nagging issues that broaden its appeal, or be powerful/general 
enough to justify it's existence on its own, or be so self-evident for a 
python user that it feels it's solving a bug.

It's not the case for ?? and friends imho, far from it.

Also, what happen if you want to modify your deep nested tree, not only 
access it?

obj?.spam?.eggs.tomato?.cheese = "Mozzarella"

will not work, and the proposal will not really help there (Or will it? I 
am not the proposer, I am strongly against it, so I could easily miss 
capabilities).
If it's not possible, you lose a kind of symmetry, and that I do not like 
(orthogonality and symmetries are really nice in in a computer language, it 
helps quickly remembering the syntax as you are not cluttered by special 
cases and exceptions)

Steven wrote:


The Python community has always been conservative and resistant to 
change, but the level of conservativeness is now pushing towards fear 
of change rather than justifiable caution about adding new features that 
cannot easily be reverted. 

That's probably because you like this proposal. Really, compared to the 2.0 
days, it seems that Python has became much less resistant to change. You 
have resistance even when proposing changes in standard library, or even 
the C interpreter internal, unseen in the Python layer, and imho it's often 
justified (what can be discussed is how arbitrary the actual selection of 
change is, but a general resistance is not a bad thing)
It is a little bit optimistic to expect ?? and friends will be a walk in 
the park, especially after := ...


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