[Python-ideas] Null coalescing operator

[Guido van Rossum]

The way I recall it, we arrived at the perfect syntax (using ?) and
semantics. The issue was purely strong hesitation about whether
sprinkling ? all over your code is too ugly for Python, and in the end
we couldn't get agreement on *that*. Another problem is PEP 505 -- it
is full of discussion but its specification is unreadable due to the
author's idea to defer the actual choice of operators and use a
strange sequence of unicode characters instead.

If someone wants to write a new, *short* PEP that defers to PEP 505
for motivation etc. and just writes up the spec for the syntax and
semantics we'll have a better starting point. IMO the key syntax is
simply one for accessing attributes returning None instead of raising
AttributeError, so that e.g. `foo?.bar?.baz` is roughly equivalent to
`foo.bar.baz if (foo is not None and foo.bar is not None) else None`,
except evaluating foo and foo.bar only once.

On Sat, Sep 10, 2016 at 10:14 AM, Random832 <random832 at fastmail.com> wrote:
> On Sat, Sep 10, 2016, at 12:48, Stephen J. Turnbull wrote:
>> I forget if Guido was very sympathetic to null-coalescing operators,
>> given somebody came up with a good syntax.
>
> As I remember the discussion, I thought he'd more or less conceded on
> the use of ? but there was disagreement on how to implement it that
> never got resolved. Concerns like, you can't have a?.b return None
> because then a?.b() isn't callable, unless you want to use a?.b?() for
> this case, or some people wanted to have "a?" [where a is None] return a
> magic object whose attribute/call/getitem would give no error, but that
> would have to keep returning itself and never actually return None for
> chained operators.
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-- 
--Guido van Rossum (python.org/~guido)