On 2018-07-23 23:05, Giampaolo Rodola' wrote:
On Mon, Jul 23, 2018 at 6:53 PM Steven D'Aprano <steve@pearwood.info> wrote:
On Mon, Jul 23, 2018 at 02:04:17PM +0200, Giampaolo Rodola' wrote:
"a?.b" does two and that's a fundamental difference (explicitness).
How is "two things" less explicit than "one thing"? Comments like the above is why I think that "explicit" and "implicit" are used to mean "I like it" and "I don't like it" rather than being objective arguments, or indeed having anything to do with explicitness or implicitness.
This:
v = a?.b
...*implicitly* checks if value is not None [and continues execution].
It's no more implicit than 'or' checking for falseness.
This:
v = a if a.b is not None: v = a.b
...*explicitly* checks if value is not None and continues execution. If for some reason '?'[ is also going to swallow LookupError then *that* would further decrease explicitness, because LookupError would be nowhere in sight, the same way "if", "is", "not", "None", ":", "new line" are nowhere in sight in the 'a?.b' example. Some argued "A ?? B" is less explicit than "A if A is not None else B" for the same reason. One may argue that silently returning None instead of raising AttributeError is also less explicit. This - and this only - is my argument about explicitness. It doesn't have to do with how many things are hidden behind an import statement or what happens on sorted() (that's comparing apples and oranges). I hope it's clear now.
It does so by introducing a brand new operator ("?") which can be spelled in two forms ("a?.b" and "a?[b]") by using two adjacent symbols not interrupted by any space, which is an absolute first in the Python syntax
It isn't a first. Many existing operators use two adjacent symbols not interrupted by a space:
e.g. == <= >= != ** // << >> += -= *= etc.
You say 'a == b'. You can't say 'a ?. b' (not that it matters, it would be less intuitive anyway). You can't because '.?' is the only couple of contiguous symbols requiring "something" before and after with no spaces in between, and that's a first in the language.
You _can_ say 'a ?. b', just as you _can_ say 'a . b'. Also, it's not a couple of contiguous symbols, it's a single symbol, just as '<=' is a single symbol (and you can't put a space in the middle of that either). [snip]