[Steve Dower <steve.do...@python.org>]
> ...
* The "``None``-aware attribute access" operator ``?.`` evaluates the
> complete expression if the left hand side evaluates to a value that is not
> ``None``
>
And if the LHS does evaluate to `None` ...? I'll assume the result is also
`None` then.
> ...
> From ``inspect.py``::
>
> for base in object.__bases__:
> for name in getattr(base, "__abstractmethods__", ()):
> value = getattr(object, name, None)
> if getattr(value, "__isabstractmethod__", False):
> return True
>
> After updating to use the ``?.`` operator (and deliberately not
> converting to use ``any()``)::
>
> for base in object.__bases__:
> for name in base?.__abstractmethods__ ?? ():
> if object?.name?.__isabstractmethod__:
> return True
>
I got lost on the `for` here. The part following `in`:
for name in getattr(base, "__abstractmethods__", ()):
looks in `base` (regardless of whether `base` is `None`) for an attribute
named "_abstractmethods__".. If such an attribute exists, the value of the
attribute is returned (`None` or not). Else an AttributeError is swallowed
and `()` is returned. It's hard to see how
for name in base?.__abstractmethods__ ?? ():
does the same. If `base` itself is `None`, I guess it returns `()`, or
if `base` has an "_abstractmethods__" attribute then the value of that
attribute is returned - unless its value is None, in which case `()` is
again returned. But if `base` is not `None` and the attribute does not
exist, doesn't this raise AttributeError? The later "Exception-aware
operators" section seemed to explicitly reject the idea that `?.` and `?[]`
would suppress AttributeError and/or TypeError.
In short, the original getattr() didn't care at all whether `base` was
`None`, or whether the value of its "__abstractmethods__" attribute was
`None`, but cared a whole lot about whether that attribute exists. I just
can't see how the updated code matches that in any of those respects.
Ignoring that and pressing on, I suffer the same kind of confusions on the
`if` part. What am I missing? For example, do these operators swallow
exceptions after all?
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