Samuele Pedroni wrote:
[...]
And having the full name of the class available would certainly help in debugging.
that's probably the only plus point but the names would be confusing wrt modules vs. classes.
You'd propably need a different separator in repr. XIST does this:
>>> from ll.xist.ns import html >>> html.a.Attrs.href <attribute class ll.xist.ns.html:a.Attrs.href at 0x8319284>
My point was that enabling reduce hooks at the metaclass level has propably other interesting applications, is far less complicated than your proposal to implement, it does not further complicate the notion of what happens at class creation time, and indeed avoids the implementation costs (for all python impls) of your proposal and still allows fairly generic solutions to the problem at hand because the solution can be formulated at the metaclass level.
Pickling classes like objects (i.e. by using the pickling methods in their (meta-)classes) solves only the second part of the problem: Finding the nested classes in the module on unpickling. The other problem is to add additional info to the inner class, which gets pickled and makes it findable on unpickling.
If pickle.py is patched along these lines [*] (strawman impl, not much
tested but test_pickle.py still passes, needs further work to support
__reduce_ex__ and cPickle would need similar changes) then this example works:
class HierarchMeta(type):
"""metaclass such that inner classes know their outer class, with pickling support"""
def __new__(cls, name, bases, dic):
sub = [x for x in dic.values() if isinstance(x,HierarchMeta)]
I did something similar to this in XIST, but the problem with this approach is that in:
class Foo(Elm): pass
class Bar(Elm): Baz = Foo
the class Foo will get its _outer_ set to Bar although it shouldn't.
[...]
def __reduce__(cls):
if hasattr(cls, '_outer_'):
return getattr, (cls._outer_, cls.__name__)
else:
return cls.__name__
I like this approach: Instead of hardcoding how references to classes are pickled (pickle the __name__), deligate it to the metaclass.
BTW, if classes and functions are pickable, why aren't modules:
>>> import urllib, cPickle
>>> cPickle.dumps(urllib.URLopener)
'curllib\nURLopener\np1\n.'
>>> cPickle.dumps(urllib.splitport)
'curllib\nsplitport\np1\n.'
>>> cPickle.dumps(urllib)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "/usr/local/lib/python2.4/copy_reg.py", line 69, in _reduce_ex
raise TypeError, "can't pickle %s objects" % base.__name__
TypeError: can't pickle module objectsWe'd just have to pickle the module name.
Bye, Walter Dörwald _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
