On Wed, Jul 25, 2018 at 9:47 PM Nicholas Chammas <nicholas.chammas@gmail.com> wrote:

> That is disingenuous, I think.  Can this raise an AttributeError?
>     spam?.eggs?.bacon
> Of course it can! And this is exactly the pattern used in many examples in
> the PEP and the discussion. So the PEP would create a situation where code
> will raise AttributeError in a slightly—and subtly—different set of
> circumstances than plain attribute access will.

 

    food = spam?.eggs?.bacon

Can be rewritten as:

    food = spam

    if spam is not None and spam.eggs is not None:

        food = spam.eggs.bacon

They both behave identically, no? Maybe I missed the point David was trying to make.

No, you illustrate it perfectly! I had to stare at your translation for a while to decide if it was really identical to the proposed `spam?.eggs?.bacon`.  The fact I have to think so hard makes the syntax feel non-obvious.  

Plus, there's the fact that your best effort at translating the proposed syntax is WRONG.  Even a strong proponent cannot explain the behavior on a first try.  And indeed, it behaves subtly different from plain attribute access in where it raises AttributeError.

>>> spam = SimpleNamespace()

>>> spam.eggs = None

>>> spam.eggs.bacon

AttributeError: 'NoneType' object has no attribute 'bacon'

>>> # spam?.eggs?.bacon

>>> # Should be: None

>>> "Translation" does something different

>>> food = spam

>>> if spam is not None and spam.eggs is not None:

...     food = spam.eggs.bacon

>>> food

namespace(eggs=None)