[Python-ideas] Fwd: Null coalescing operator

[Bruce Leban]

On Sat, Sep 10, 2016 at 6:02 PM, David Mertz <mertz at gnosis.cx> wrote:

> What I was getting at with "essentially" was that it would *do the same
> thing* that an AttributeError does.  That is, if `x.foo` can't be evaluated
> (i.e. x doesn't have an attribute 'foo'), then access is informally "an
> error."  The hypothetical "x?.foo" catches that "error" and substitutes a
> different value.  The particular implementation under-the-hood is less
> important for most programmers who might use the construct (and I think
> documentation would actually give an informal equivalent as something
> similar to what I put in the NoneCoalesce class).
>

That's not a good way to think about it. This new operator is only checking
for None and not actually checking for AttributeErrors. Consider:

(3).x    # AttributeError
{}.x     # AttributeError

None.x   # AttributeError


(3)?.x   # still AttributeError

{}?.x    # still AttributeError

None?.x  # None


And also:

None.__class__   # <type 'NoneType'>

None?.__class__  # None


And it's certainly not the case that those values don't accept any
attributes:

(3).real        # 3
{}.values       # <built-in method ...>
None.__class__  #<type 'NoneType'>

--- Bruce
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