Am Freitag, 14. Oktober 2016 23:11:48 UTC-7 schrieb Nick Coghlan:
Regarding the spelling details, my current preferences are as follows:
* None-coalescing operator: x ?or y * None-severing operator: x ?and y * None-coalescing augmented assignment: x ?= y * None-severing attribute access: x?.attr * None-severing subscript lookup: x?[expr]
This is, more or less, the syntax added in Nick's PEP 531 draft <https://www.python.org/dev/peps/pep-0531/>. The reddit discussion <https://www.reddit.com/r/Python/comments/59d2he/pep_531_existence_checking_o...> about it raised some pretty major concerns about clarity, and I have to admit, I think if you're learning Python as a first language, the ?and, ?else, x?.attr, etc syntax is likely to be very confusing. For me personally, combining a new operator "?" with existing keywords like "and" or "else" just does not make any intuitive sense. I definitely see the value, though, in particular of None-severing, especially as a tool to explicitly specify which attr can be missing -- ie, disambiguating which attribute is missing in a foo.bar.baz lookup (the alternative to which is nested try: except AttributeError: blocks, which gets very messy very quickly). I'm on board with the idea, and I can absolutely imagine using it in my code, but I disagree on the spelling. A thought I had (perhaps more readable in a reddit comment <https://www.reddit.com/r/Python/comments/59d2he/pep_531_existence_checking_o...>) is to condense everything into a single "?" symbol, used for: + Coalescing binary operator: foo ? bar + Coalescing augmented assignment operator: foo ?= bar + Severing unary operator: ?foo *Pseudocode binary operator examples:*
foo_exists ? bar_never_evaluated foo_exists
foo_missing ? foo_exists foo_exists
foo_missing ? bar_missing foo_missing
*Pseudocode augmented examples:*
foo_exists = 'foo' foo_exists ?= bar_never_evaluated foo_exists == 'foo' True
foo = Missing bar_exists = 'bar' foo ?= bar_exists foo == 'bar' True
foo = None bar_missing = Missing foo ?= bar_missing foo == None True
*Pseudocode unary examples:*
?(foo_exists).bar.baz foo_exists.bar.baz ?(foo_exists)[bar][baz] foo_exists[bar][baz]
?(foo_missing).bar.baz Missing ?(foo_missing)[bar][baz] Missing
?(foo_exists).bar.baz_missing Traceback... AttributeError: <foo_exists.bar> object has no attribute 'baz_missing' ?(foo_exists)[bar][baz_missing] Traceback... KeyError: 'baz_missing'
?(foo_missing).bar.baz_missing Missing ?(foo_missing)[bar][baz_missing] Missing
I personally think that's substantially more readable, but I suppose that's at least somewhat a matter of personal preference.