On Mon, Sep 28, 2015 at 10:38 AM, Carl Meyer <carl@oddbird.net> wrote:
On 09/28/2015 11:29 AM, Guido van Rossum wrote:
On Mon, Sep 28, 2015 at 9:02 AM, Jeff Hardy <jdhardy@gmail.com <mailto:jdhardy@gmail.com>> wrote:
-1 on the propagating member-access or index operators
Can someone explain with examples what this refers to?
"Member-access or index operators" refers to the proposed ?. or ?[ operators.
Got that. :-)
"Propagating" refers to the proposed behavior where use of ?. or ?[ "propagates" through the following chain of operations. For example:
x = foo?.bar.spam.eggs
Where both `.spam` and `.eggs` would behave like `?.spam` and `?.eggs` (propagating None rather than raising AttributeError), simply because a `.?` had occurred earlier in the chain. So the above behaves differently from:
temp = foo?.bar x = temp.spam.eggs
Which raises questions about whether the propagation escapes parentheses, too:
x = (foo?.bar).spam.eggs
Oh, I see. That's evil. The correct behavior here is that "foo?.bar.spam.eggs" should mean the same as (None if foo is None else foo.bar.spam.eggs) (Stop until you understand that is *not* the same as either of the alternatives you describe.) I can see the confusion that led to the idea of "propagation" -- it probably comes from an attempt to define "foo?.bar" without reference to the context (in this case the relevant context is that it's followed by ".spam.eggs"). It should not escape parentheses. -- --Guido van Rossum (python.org/~guido)