| msg250468 - (view) |
Author: Antti Haapala (ztane) * |
Date: 2015-09-11 13:03 |
| User DeTeReR asked a question (http://stackoverflow.com/questions/32521140/generator-as-function-argument) on Stack Overflow about a special case of code that seemed to work in Python 3.4: f(1 for x in [1], *[2]) and f(*[2], 1 for x in [1]) I found out that when Python 2.6 introduced the "keyword arguments after *args", the checks in ast.c did not follow: for (i = 0; i < NCH(n); i++) { node *ch = CHILD(n, i); if (TYPE(ch) == argument) { if (NCH(ch) == 1) nargs++; else if (TYPE(CHILD(ch, 1)) == gen_for) ngens++; else nkeywords++; } } if (ngens > 1 | |
(ngens && (nargs |
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| msg250469 - (view) |
Author: STINNER Victor (vstinner) *  |
Date: 2015-09-11 13:15 |
| I guess that it's a consequence of the PEP 448 "additional unpacking generalizations". |
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| msg250470 - (view) |
Author: Antti Haapala (ztane) * |
Date: 2015-09-11 13:25 |
| @haypo yes. I must add that I found out that Python 2.5 also allows f(1 for x in [1], *a) and f(1 for x in [1], **kw) but not f(*a, 1 for x in [1]) So I do not know if the first and second cases were intentional or not. Also, in Python 2.6 - 3.4, f(*a, 1 for x in [1]) provides the generator as the *first* positional argument, in 3.5 it'd be the last one. |
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| msg250471 - (view) |
Author: Stefan Krah (skrah) * |
Date: 2015-09-11 13:46 |
| According to the human readable grammar in the docs https://docs.python.org/3/reference/expressions.html#calls I'd say this was a bug that is now fixed in 3.5. The call should either take a single unparenthesized generator expression or an argument_list (which may contain parenthesized generator expressions). |
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| msg250473 - (view) |
Author: Antti Haapala (ztane) * |
Date: 2015-09-11 13:50 |
| Yeah, it is a bug in 2.5 too; https://docs.python.org/2.5/ref/calls.html call ::= primary "(" [argument_list [","] | expression genexpr_for] ")" |
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| msg250500 - (view) |
Author: R. David Murray (r.david.murray) * |
Date: 2015-09-11 21:40 |
| If we have decided that this is a "fixed bug", it should indeed be mentioned in what's new for 3.5 since it is a behavior change. |
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| msg250511 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-09-12 03:36 |
| > If we have decided that this is a "fixed bug", [..] I'd call this a bug fix. The old syntax was completely unreadable. Should I close this issue? > [..] it should indeed be mentioned in what's new for 3.5 since it is a behavior change. Sure, I'll document it. |
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| msg250519 - (view) |
Author: Stefan Krah (skrah) * |
Date: 2015-09-12 12:10 |
| I think the issue can be closed (after updating "what's new"). Even if we wanted to keep backwards compatibility, it's too late now. |
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| msg250535 - (view) |
Author: Roundup Robot (python-dev)  |
Date: 2015-09-12 21:51 |
| New changeset 10a9d4acd9cb by Yury Selivanov in branch '3.5': whatsnew/3.5 More edits https://hg.python.org/cpython/rev/10a9d4acd9cb |
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| msg250536 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-09-12 21:52 |
| What's new is now updated with description of this issue. Closing it now. |
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