Possibly relevant for tilde: https://www.thecut.com/article/why-the-internet-tilde-is-our-most-perfect-tool-for-snark.html
On Thu, Aug 29, 2019 at 5:09 PM Dominik Vilsmeier <dominik.vilsme...@gmx.de> wrote: > Guido van Rossum wrote: > > On Thu, Aug 29, 2019 at 4:04 PM Dominik Vilsmeier > dominik.vilsme...@gmx.de > > wrote: > > > I never really understood the importance of > > > Optional. Often it can be > > > left out altogether and in other cases I find Union[T, None] more > > > expressive (explicit) than Optional[T] (+ the latter saves only 3 > > > chars). > > > I respectfully disagree. In our (huge) codebase we see way more > occurrences > > of Optional than of Union. It's not that it saves a tremendous amount of > > typing -- it's a much more intuitive meaning. Every time I see Union[T, > > None] I have to read it carefully to see what it means. When I see > > Optional[T] my brain moves on immediately (in a sense it's only one bit > of > > information). > > You are probably right, it's all a matter of how used our brains are to > seeing stuff. So if I started using it more frequently, after some time I > would probably appreciate it over `Union[T, None]`. > > > > Especially for people not familiar with typing, the > > > meaning of Optional > > > is not obvious at first sight. Union[T, None] on the other hand is > pretty > > > clear. Also in other cases, where the default (fallback) is different > from > > > None, you'd have to use Union anyway. For example a function > > > that > > > normally returns an object of type T but in some circumstances it > cannot > > > and then it returns the reason as a str, i.e. -> Union[T, > > > str]; > > > Optional won't help here. Scanning through the docs and PEP I can't > find > > > strongly motivating examples for Optional (over Union[T, None]). > > > E.g. > > > in the following: > > > def lookup(self, name: str) -> Optional[Node]: > > > nodes = self.get(name) > > > if nodes: > > > return nodes[-1] > > > return None > > > > > > I would rather write Union[Node, None] because that's much more > explicit > > > about what happens. > > > Then introducing ~T in place of Optional[T] just further > > > obfuscates > > > the meaning of the code: > > > def lookup(self, name: str) -> ~Node: > > > > > > The ~ is easy to be missed (at least by human readers) and the meaning > > > not obvious. > > > Do you easily miss the - in an expression like -2? > > I don't miss the `-` in the context because my brain is trained on > recognizing such patterns. We encounter negative numbers everywhere, from > (pre-)school on, so this pattern is easy to recognize. However `~Noun` is > not something you've likely seen in the real world (or anywhere), so it's > much harder to recognize. I cn wrt ths txt wtht vwls or eevn rdoerer teh > lterets and you'll still be able to read it because your brain just fills > in what it expects (i.e. what it is accustomed to). For that reason `~Node` > is much harder to recognize than `-3637` because I wouldn't expect a `~` to > appear in that place. > > > Surely the meaning of ? in a programming language also has to be learned. > > And not every language uses it to mean "optional" (IIRC there's a > language > > where it means "boolean" -- maybe Scheme?) > > > For Union on the other hand it would be > > > more helpful to have a shorter > > > syntax, int | str seems pretty clear, but what prevents tuples (int, > > > str) from being interpreted as unions by type checkers. This doesn't > > > require any changes to the built-in types and it is aligned with the > > > already existing syntax for checking multiple types with isinstance or > > > issubclass: isinstance(x, (int, str)). Having used this a couple > > > of > > > times, whenever I see a tuple of types I immediately think of them as > or > > > options. > > > First, if we were to introduce (int, str) it would make > > more sense for > > it to mean Tuple[int, str] (tuples are also a very common type). Second, > > comma is already very overloaded. > > Yes, it's unfortunately that (int, str) means "union" in > > isinstance() > > but it's not enough to sway me. > > Anyway, let's just paint the bikeshed some color. :-) > > I don't think it's unfortunate, it's pretty neat syntax (and intuitive). > Checking if `x` is an instance of `y` it makes sense to "list" (`tuple`) > multiple options for `y`. It's a clever way of reusing the available syntax > / functionality of the language. And I think this is what typing should do > as well: build around the existing language and use whatever is available. > Adding `__or__` to `type` for allowing things like `int | str` on the other > hand bends the language toward typing and thus is a step in the opposite > direction. > > Then I don't think it's the comma that receives emphasis in the syntax > `(int, str)`, it's rather the parens - and those, as a bonus, provide > visual boundaries for the beginning and end of the union. Consider > > def foo(x: str | int, y: list): > > versus > > def foo(x: (str, int), y: list): > > The comma is a small character, visually the scene will be dominated by > the matching parens - and whatever is inside is anyway a common sight as we > are used to seeing tuples. Hence I think from readability perspective it's > a plus to reuse existing, common syntax. > > I agree that there is the ambiguity with `(int, str)` being interpreted as > `Tuple[int, str]` and this is a valid argument. Since I've used the > `isinstance(x, (y,z))` syntax quite often I wouldn't interpret `(int, str)` > as a tuple but of course for other people the situation might be completely > different. Hence that could really be a blocker. > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/ZONQON7O46YC666CGBBZ3XDX7SBWITOU/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him/his **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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