[Python-Dev] Tricky way of of creating a generator via a comprehension expression (original) (raw)
David Mertz mertz at gnosis.cx
Wed Nov 22 15:29:42 EST 2017
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Inasmuch as I get to opine, I'm +1 on SyntaxError. There is no behavior for that spelling that I would find intuitive or easy to explain to students. And as far as I can tell, the ONLY time anything has ever been spelled that way is in comments saying "look at this weird edge case behavior in Python."
On Nov 22, 2017 10:57 AM, "Jelle Zijlstra" <jelle.zijlstra at gmail.com> wrote:
2017-11-22 9:58 GMT-08:00 Guido van Rossum <guido at python.org>:
Wow, 44 messages in 4 hours. That must be some kind of record.
If/when there's an action item, can someone summarize for me? The main disagreement seems to be about what this code should do:
g = [(yield i) for i in range(3)]Currently, this makes g into a generator, not a list. Everybody seems to
agree this is nonintuitive and should be changed.
One proposal is to make it so g gets assigned a list, and the yield
happens in the enclosing scope (so the enclosing function would have to be
a generator). This was the way things worked in Python 2, I believe.
Another proposal is to make this code a syntax error, because it's confusing either way. (For what it's worth, that would be my preference.)
There is related discussion about the semantics of list comprehensions versus calling list() on a generator expression, and of async semantics, but I don't think there's any clear point of action there.
-- --Guido van Rossum (python.org/~guido)
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