[issue9117] class syntax not fully documented in reference manual
New submission from Mark Dickinson dickinsm@gmail.com:
Looking at:
http://docs.python.org/dev/py3k/reference/compound_stmts.html#class-definiti...
I see:
classdef ::= [decorators] "class" classname [inheritance] ":" suite inheritance ::= "(" [expression_list] ")" classname ::= identifier
this seems to be missing the keyword arguments that are now possible in a classdef (e.g. for specifying a metaclass). I believe that *args and **kwargs are now also syntactically accepted in a class definition.
---------- assignee: docs@python components: Documentation messages: 108917 nosy: docs@python, mark.dickinson priority: normal severity: normal status: open title: class syntax not fully documented in reference manual versions: Python 3.1, Python 3.2
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Mark Dickinson dickinsm@gmail.com added the comment:
Am working on a patch.
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Alexander Belopolsky belopolsky@users.sourceforge.net added the comment:
I believe that *args and **kwargs are now also syntactically accepted in a class definition.
Indeed:
class a: pass class b: pass bases = (a, b) class c(*bases): pass kwds = {'metaclass':type} class c(*bases, **kwds): pass
works!
---------- nosy: +belopolsky
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Mark Dickinson dickinsm@gmail.com added the comment:
It looks like fixing the production list is the easy part (see attached patch): as far as I can tell, the *syntax* for class definitions is pretty much identical to that for function calls. (The semantics are different, of course.) It would be good if someone could check this patch for sanity, though.
The description in that section still needs updating.
---------- keywords: +patch Added file: http://bugs.python.org/file17802/issue9117.patch
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Alexander Belopolsky belopolsky@users.sourceforge.net added the comment:
The production looks right to me, but I think it should be broken in two or more lines. Since it is rendered pre-formatted, long line results in a horizontal scroll bar unless the browser window is extremely wide.
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Mark Dickinson dickinsm@gmail.com added the comment:
Yes, good plan. I'll do that.
I'm also not sure about the 'comprehension' bit; it's true that a comprehension is syntactically valid here (e.g., "class A(x for x in range(3))"), but it's also entirely useless: it has to be the sole argument, so there can't be a metaclass argument, so the metaclass would have to be type. But type (quite sensibly) won't accept a generator as a base class.
Oh well; I suppose it doesn't *have* to make sense to be valid syntax...
This still leaves the hard part, which is distilling the essence of PEP 3115 and adding it to the reference manual.
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Mark Dickinson dickinsm@gmail.com added the comment:
Updated patch. I've reorganized that documentation section a bit, and added a link to PEP 3115. This isn't ideal, but it's better than nothing.
---------- Added file: http://bugs.python.org/file17805/issue9117_v2.patch
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Mark Dickinson dickinsm@gmail.com added the comment:
And the same patch, but this time *without* the irrelevant audioop changes. :)
---------- Added file: http://bugs.python.org/file17806/issue9117_v2.patch
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Changes by Mark Dickinson dickinsm@gmail.com:
Removed file: http://bugs.python.org/file17805/issue9117_v2.patch
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Georg Brandl georg@python.org added the comment:
This patch was mostly out-of-date since PEP 3115 metaclasses are now documented; I've merged what was missing in r85626.
---------- nosy: +georg.brandl resolution: -> fixed status: open -> closed
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participants (3)
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Alexander Belopolsky -
Georg Brandl
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Mark Dickinson