On 2020-12-29 15:01, Christopher Barker wrote:
along with a COMPLETE list of
the language features that make use of that protocol.
That is pretty much impossible -- that's kind of the point of a protocol
-- it can be used in arbitrary places in arbitrary code.
would you expect a COMPLETE list of all the language features that
use the iteration protocol?
Yes, but perhaps not as complete as you thought I meant. :-) What I
mean by "language features" here is basically syntactic features that
IMPLICITLY invoke the protocol.
Certainly arbitrary code can use a protocol the sense that any function
can call some other function that eventually winds up using the
protocol. Also, code can explicitly invoke the iterator protocol, by,
e.g., calling obj.__next__(), but that's not a problem because you can
easily look up how the object defines __next__. The magic part is when
you have something like `for x in obj`, which includes not even any
indirect references (i.e., in called functions) to `__iter__` or
`__next__`, yet winds up calling them. And it's because that is magic
that we need to make it very explicit.
So by a complete list of language features that use iteration I would
mean. . . well, this is why we need to do this, to make sure we get them
all! :-) But the idea is that all usages of the iterator protocol
should funnel through a small number of entrypoints --- that's the point
of a protocol, in some sense. So the list would be: `for` (including
comprehensions), the builtin functions `next` and `iter` because they're
sort of a manual crank of the protocol. . . is there anything else?
Maybe `yield` because it implicitly creates objects that implement the
protocol?
That's the kind of "complete list" I mean. I'm not including things
like library functions that happen to iterate over stuff. The whole
point of the iterator protocol is that it defines iteration, so every
such function can say "this function iterates over obj" (with a link to
the protocol!) and that's enough. But cases where syntax implicitly
invokes the protocol, those are the ones that must be exhaustively listed.
--
Brendan Barnwell
"Do not follow where the path may lead. Go, instead, where there is no
path, and leave a trail."
--author unknown
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