New submission from Terry J. Reedy:
https://docs.python.org/3/reference/expressions.html#yield-expressions says "When yield from <expr> is used, it treats the supplied expression as a subiterator. All values produced by that subiterator ...". To me "treats..expression as a subiterator" means that the expression must *be* an iterator, such as returned by iter or calling a generator function. Hence I was surprised upon reading "yield from <non-iterator iterable>" in stdlib code.
I confirmed that this usage is correct by trying
yield from (1,2)
i = g() next(i), next(i)
and then reading the PEP380 Formal Semantics, which begins with "_i = iter(EXPR)". Hence I suggest the following replacement for the quote above: "When yield from <expr> is used, the expression must be an iterable. A subiterator is obtained with iter(<expr>). All values produced by that subiterator ...".
Note that 'subiterator' is spelled in the following sentences 'underlying iterable' (which I am not sure I like) and 'sub-iterator' (and 'sub-generator'). I think we should be consistent for at least the two short 'yield from' paragraphs.
---------- assignee: docs@python components: Documentation messages: 271577 nosy: docs@python, terry.reedy priority: normal severity: normal stage: patch review status: open title: yield from expression can be any iterable type: behavior versions: Python 3.5, Python 3.6