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bpo-27646: Say that 'yield from' expression can be any iterable #24595

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Merged
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Feb 21, 2021
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bpo-27646: Say that 'yield from' expression can be any iterable #24595

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4 changes: 2 additions & 2 deletions Doc/reference/expressions.rst
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Expand Up @@ -478,8 +478,8 @@ allowing any pending :keyword:`finally` clauses to execute.
.. index::
single: from; yield from expression

When ``yield from <expr>`` is used, it treats the supplied expression as
a subiterator. All values produced by that subiterator are passed directly
When ``yield from <expr>`` is used, the supplied expression must be an
iterable. The values produced by iterating that iterable are passed directly
to the caller of the current generator's methods. Any values passed in with
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Is "the current generator's methods" the correct term to use here? (Should it be "the current generator method" or something like that?)

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Good question. I believe the answer is yes, this part of the doc was and is correct. The 'current generator' is the one with 'yield from'. The two methods for getting yielded values are __next__ and send.

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methods could be expanded to '__next__' or 'send' method. (with markup). I notice that the two methods to pass things into the generator are explicitly named in the next sentence. What do you think?

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I see what you mean. Though I'm not sure "passed directly to the caller of ... " is that clear either. Maybe this whole sentence can be rephrased/simplified?

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"The values produced by iterating that iterable form part of the current generator's output." or some such?

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I want to stick with the defined scope of the issue, to replace the ambiguous or incorrect 'subiterator' in these two sentences, so it is clear what one can pass to 'yield from'. Do you have any comment on my replacements?. After sleeping on them, I think them good enough and am ready to merge.

I have also wondered about the exact meaning of 'passed directly', but the visible effect would what lines of code appear in a trace. Does 'passed directly' mean that the 'yield from' line would not appear? I suspect so; but if I cared I would run experiments. I consider this a separate issue.

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Yes, the part you changed looks fine.

:meth:`~generator.send` and any exceptions passed in with
:meth:`~generator.throw` are passed to the underlying iterator if it has the
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Documentation/2021-02-20-00-09-13.bpo-27646.HRsmo-.rst
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@@ -0,0 +1,2 @@
Clarify that 'yield from <expr>' works with any iterable, not just
iterators.