[Python-ideas] PEP 505 (None coalescing operators) thoughts

Carl Meyer carl at oddbird.net
Mon Sep 28 19:38:03 CEST 2015

On 09/28/2015 11:29 AM, Guido van Rossum wrote:
> On Mon, Sep 28, 2015 at 9:02 AM, Jeff Hardy <jdhardy at gmail.com
> <mailto:jdhardy at 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 ?[

"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

    temp = foo?.bar
    x = temp.spam.eggs

Which raises questions about whether the propagation escapes
parentheses, too:

    x = (foo?.bar).spam.eggs


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