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
>>> def g():
yield from (1,2)
>>> i = g()
>>> next(i), next(i)
(1, 2)
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
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Python tracker <[email protected]>
<http://bugs.python.org/issue27646>
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