[issue14588] PEP 3115 compliant dynamic class creation
Roundup Robot devn...@psf.upfronthosting.co.za added the comment: New changeset befd56673c80 by Nick Coghlan in branch 'default': Close #14588: added a PEP 3115 compliant dynamic type creation mechanism http://hg.python.org/cpython/rev/befd56673c80 -- nosy: +python-dev resolution: - fixed stage: - committed/rejected status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Éric Araujo mer...@netwok.org added the comment: Great doc patch. I think it would be worthwhile to backport it. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Daniel Urban urban.dani...@gmail.com added the comment: Here is my first attempt at creating a pure Python version of the operator.build_class function (in my previous patch) as types.new_class. The three added functions (two private and one public) correspond to the following functions in my previous patch: types.new_class - operator.build_class types._prepare_ns - prepare_namespace in typeobject.c types._calculate_mcls - calculate_metaclass in typeobject.c (currently _PyType_CalculateMetaclass) (In Python these functions are quite short, so they may be merged. But this separation may be better for documentation purposes...) The tests are mostly the same as in my previous patch. -- components: +Library (Lib) Added file: http://bugs.python.org/file25546/types_new_class.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Éric Araujo mer...@netwok.org added the comment: Implementing in pure Python seems to have a lot of pros and no con to me. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Nick Coghlan ncogh...@gmail.com added the comment: Based on the python-dev thread [1], the proposed name for this API is now types.new_class(). This parallels the existing imp.new_module() naming scheme and avoids various problems with the idea of using a static method on type itself (descriptors on type behave strangely, and the type namespace is accessible through *all* type objects, which would be weird in this case). Since types is a Python module, we now have to choose between 3 implementation strategies: - reimplement in pure Python (my preferred choice) - implement in terms of __build_class__ (would work, but may not be portable to other implementations and/or serves as a de facto promotion of __build_class__ up to being part of the language specification) - move Daniel's existing operator module based solution over to a new _types C extension module (again, may not help other implementations) The reason I find the idea of a pure Python reimplementation appealing is that it can then serve as a cross-check for any other implementations implementing PEP 3115 for their class statements. [1] http://mail.python.org/pipermail/python-dev/2012-May/119318.html -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Nick Coghlan ncogh...@gmail.com added the comment: In going to add documentation for your patch, I realised the operator module is not the right place for this. The types module actually seems like the most appropriate home, but that will require adding a _types module to back it. I'll post to python-dev to get additional feedback. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Daniel Urban urban.dani...@gmail.com added the comment: I've attached the third patch with the eval_body - exec_body change; explicitly passing the default (None) now also allowed. I also fixed a refleak (I think). -- Added file: http://bugs.python.org/file25292/operator_build_class_3.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Daniel Urban urban.dani...@gmail.com added the comment: Fair enough. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Nick Coghlan ncogh...@gmail.com added the comment: It occurs to me that, for naming consistency, the callback arg should be documented as exec_body rather than eval_body. I'll try to get to a proper patch review this weekend. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Changes by R. David Murray rdmur...@bitdance.com: -- nosy: +r.david.murray ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Daniel Urban urban.dani...@gmail.com added the comment:
I've attached a patch with more tests. I simply copied and modified the tests
about metaclass calculation and __prepare__ in test_descr.py, to create the
tested classes with operator.build_class (and not the class statement).
Although, there is one thing I'm not sure I like about the API in the current
patch: the dictionary corresponding to the keyword arguments of the class
statement cannot be passed as keyword arguments. For example, I can't write
this:
C = operator.build_class('C', (A, B), metaclass=MyMeta)
I have to write this:
C = operator.build_class('C', (A, B), {'metaclass': MyMeta})
(The reason for this is that the eval_body argument is the last.)
What would you think about the following signature for build_class?
build_class(name, bases=(), eval_body=None, **kwargs)
The fist 3 argument could be positional only, and all keyword arguments would
go into the dict. A downside is that the user would have to explicitly pass
None as the 3rd argument, if they don't need an eval_body, but need
keyword-arguments. Also, the 'bases' and the keyword arguments wouldn't be
close to each other as in the class statement...
--
Added file: http://bugs.python.org/file25263/operator_build_class_2.patch
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[issue14588] PEP 3115 compliant dynamic class creation
Nick Coghlan ncogh...@gmail.com added the comment:
I thought about that, and I'd prefer a dedicated dictionary to avoid questions
of name conflicts.
Wrapping the keyword args in a dict() call is still pretty clean:
C = operator.build_class('C', (A, B), dict(metaclass=MyMeta))
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[issue14588] PEP 3115 compliant dynamic class creation
Changes by R. David Murray rdmur...@bitdance.com: -- assignee: - ncoghlan ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
Changes by Éric Araujo mer...@netwok.org: -- nosy: +eric.araujo ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue14588 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14588] PEP 3115 compliant dynamic class creation
New submission from Daniel Urban urban.dani...@gmail.com:
As Nick Coghlan proposed [1, 2], there should be a way to dynamically create
classes, which handles metaclasses correctly (see also issue1294232).
Here is my first attempt at creating an operator.build_class method. It only
includes very simple tests and no documentation, but I will write them if
needed.
With this patch there are two functions for creating a class object:
1. __build_class__ (no change)
2. operator.build_class(name, bases=(), kwds=None, eval_body=None): finds the
correct metaclass and calls its __prepare__. If eval_body is given, calls it
with the namespace returned by __prepare__. Then calls the correct metaclass,
and returns the created class object.
Both of these functions (after parsing their arguments) call
_PyType_BuildClass, a new C API function. The first argument of this function
is a callable, that will be called with the namespace returned by __prepare__
(it also can be NULL, in that case nothing will be called). __build_class__
passes the function that is the body of the class statement.
operator.build_class passes the callable given by the user (or NULL, if the
user didn't pass the eval_body argument). The implementation of
_PyType_BuildClass is approximately the following:
def _PyType_BuildClass(func=None, name, bases, kwds={}):
meta = kwds.pop('metaclass', None)
if meta is None:
if not bases:
meta = type
else:
meta = type(bases[0])
ns, meta = prepare_namespace(name, meta, bases, kwds)
if func is not None:
func(ns)
return meta(name, bases, ns, kwds)
(Actually the return value of the func is used if it's a cell object. I'm not
sure, why and when this is needed, this code comes from __build_class__.)
The changes are in the following files:
1. object.h: the exported function is _PyType_BuildClass instead of
_PyType_CalculateMetaclass (that doesn't need to be in the include file
anymore).
2. operator.c: the build_class method checks its arguments, then calls
_PyType_BuildClass.
3. typeobject.c:
_PyType_CalculateMetaclass is renamed to calculate_metaclass, because now it is
only called from this file.
prepare_namespace calls calculate_metaclass to determine the correct metaclass,
then calls its __prepare__ method. (This code is moved here mostly from
__build_class__). It also passes back the correct metaclass to its caller.
_PyType_BuildClass gets the starting metaclass from its arguments. Then it
calls prepare_namespace to get the namespace and the correct metaclass. If it
received a non-NULL first argument (the function that is the class body or the
eval_body argument of operator.build_class), then calls it, passing the
namespace. Then it calls the correct metaclass. (Most of this code is also from
__build_class__.)
4. bltinmodule.c: builtin___build_class__ now only parses its arguments, and
simply calls _PyType_BuildClass.
5. test_operator.py: a simple test for operator.build_class
[1] http://mail.python.org/pipermail/python-dev/2011-April/110874.html
[2] http://mail.python.org/pipermail/python-dev/2012-April/118732.html
--
components: Extension Modules, Interpreter Core
files: operator_build_class.patch
keywords: patch
messages: 158382
nosy: durban, ncoghlan
priority: normal
severity: normal
status: open
title: PEP 3115 compliant dynamic class creation
type: enhancement
versions: Python 3.3
Added file: http://bugs.python.org/file25231/operator_build_class.patch
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