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doc: yield from expression can be any iterable #71833

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terryjreedy opened this issue Jul 28, 2016 · 4 comments
Closed

doc: yield from expression can be any iterable #71833

terryjreedy opened this issue Jul 28, 2016 · 4 comments
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3.8 only security fixes 3.9 only security fixes 3.10 only security fixes docs Documentation in the Doc dir type-bug An unexpected behavior, bug, or error

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@terryjreedy
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BPO 27646
Nosy @terryjreedy, @miss-islington
PRs
  • bpo-27646: Say that 'yield from' expression can be any iterable #24595
  • [3.9] bpo-27646: Say that 'yield from' expression can be any iterable (GH-24595) #24602
  • [3.8] bpo-27646: Say that 'yield from' expression can be any iterable (GH-24595) #24603
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    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
closed_at = <Date 2021-02-21.05:40:52.786>
created_at = <Date 2016-07-28.18:30:50.864>
labels = ['type-bug', '3.8', '3.9', '3.10', 'docs']
title = 'doc: yield from expression can be any iterable'
updated_at = <Date 2021-02-21.05:40:52.785>
user = 'https://github.com/terryjreedy'

    bugs.python.org fields:

    activity = <Date 2021-02-21.05:40:52.785>
actor = 'terry.reedy'
assignee = 'docs@python'
closed = True
closed_date = <Date 2021-02-21.05:40:52.786>
closer = 'terry.reedy'
components = ['Documentation']
creation = <Date 2016-07-28.18:30:50.864>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 27646
keywords = ['patch']
message_count = 4.0
messages = ['271577', '387435', '387436', '387437']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'docs@python', 'miss-islington']
pr_nums = ['24595', '24602', '24603']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27646'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']
    @terryjreedy
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    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 PEP-380 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.

    @terryjreedy terryjreedy added docs Documentation in the Doc dir type-bug An unexpected behavior, bug, or error labels Jul 28, 2016
    @iritkatriel iritkatriel added the 3.10 only security fixes label Feb 19, 2021
    @iritkatriel iritkatriel changed the title yield from expression can be any iterable doc: yield from expression can be any iterable Feb 19, 2021
    @terryjreedy
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    New changeset 2f9ef51 by Terry Jan Reedy in branch 'master':
    bpo-27646: Say that 'yield from' expression can be any iterable (GH-24595)
    2f9ef51

    @miss-islington
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    New changeset 089a21f by Miss Islington (bot) in branch '3.8':
    bpo-27646: Say that 'yield from' expression can be any iterable (GH-24595)
    089a21f

    @miss-islington
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    New changeset 7cc5889 by Miss Islington (bot) in branch '3.9':
    bpo-27646: Say that 'yield from' expression can be any iterable (GH-24595)
    7cc5889

    @terryjreedy terryjreedy added 3.8 only security fixes 3.9 only security fixes labels Feb 21, 2021
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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