[Python-ideas] PEP 505: None-aware operators

[Stephan Houben]

Op wo 1 aug. 2018 11:10 schreef Jonathan Fine <jfine2358 at gmail.com>:

>
>
> You're right to be cautious. My understanding of PEP 505 is that
> #13.  a ?. b ?. __str__
> #14. (a ?. b) ?. __str__
> are not equivalent. The first is None, and the other is None.__str__.
> That looks like a gotcha.
>


No.
None.?__str__
produces None, even though None has a __str__ attribute.

I am pretty sure
a?.b?.c == (a?.b)?.c

and more generically

chain_A ?. chain_B == (chain_A) ?. chain_B

Stephan


> (By the way, it was not my intention to catch you out. I'm simply
> looking for clarity. I wasn't aware of the gotcha until I started
> answering myself the question I had asked you.)
>
> However, the None object is somewhat special, in that all it's methods
> and double-under (dunder) methods. And one of them is __bool__.  And
> we can't add or change the attributes of None.
>
> Chris, you don't have to reply to this. But I would be pleased if an
> expert could either tell me that my neck is safe, or produce a value
> of 'a' that cuts it off (so to speak).
>
> --
> Jonathan
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