Um, what?! __class__ *already* has a special meaning. Those examples violate that meaning. No wonder they get garbage results.
The correct way to override isinstance is explained here: http://www.python.org/dev/peps/pep-3119/#overloading-isinstance-and-issubclass . --Guido On Sat, Nov 19, 2011 at 6:13 PM, Michael Foord <fuzzy...@voidspace.org.uk> wrote: > > > On 19 November 2011 23:11, Vinay Sajip <vinay_sa...@yahoo.co.uk> wrote: >> >> Michael Foord <fuzzyman <at> voidspace.org.uk> writes: >> >> > That works fine in Python 3 (mock.Mock does it): >> > >> > >>> class Foo(object): >> > ... @property >> > ... def __class__(self): >> > ... return int >> > ... >> > >>> a = Foo() >> > >>> isinstance(a, int) >> > True >> > >>> a.__class__ >> > <class 'int'> >> > >> > There must be something else going on here. >> > >> >> Michael, thanks for the quick response. Okay, I'll dig in a bit further: >> the >> definition in SimpleLazyObject is >> >> __class__ = property(new_method_proxy(operator.attrgetter("__class__"))) >> >> so perhaps the problem is something related to the specifics of the >> definition. >> Here's what I found in initial exploration: >> >> -------------------------------------------------------------------------- >> Python 2.7.2+ (default, Oct 4 2011, 20:06:09) >> [GCC 4.6.1] on linux2 >> Type "help", "copyright", "credits" or "license" for more information. >> >>> from django.utils.functional import SimpleLazyObject >> >>> fake_bool = SimpleLazyObject(lambda: True) >> >>> fake_bool.__class__ >> <type 'bool'> >> >>> fake_bool.__dict__ >> {'_setupfunc': <function <lambda> at 0xca9ed8>, '_wrapped': True} >> >>> SimpleLazyObject.__dict__ >> dict_proxy({ >> '__module__': 'django.utils.functional', >> '__nonzero__': <function inner at 0xca9de8>, >> '__deepcopy__': <function __deepcopy__ at 0xca9c08>, >> '__str__': <function inner at 0xca9b18>, >> '_setup': <function _setup at 0xca9aa0>, >> '__class__': <property object at 0xca5730>, >> '__hash__': <function inner at 0xca9d70>, >> '__unicode__': <function inner at 0xca9b90>, >> '__bool__': <function inner at 0xca9de8>, >> '__eq__': <function inner at 0xca9cf8>, >> '__doc__': '\n A lazy object initialised from any function.\n\n >> Designed for compound objects of unknown type. For builtins or >> objects of\n known type, use django.utils.functional.lazy.\n ', >> '__init__': <function __init__ at 0xca9a28> >> }) >> -------------------------------------------------------------------------- >> Python 3.2.2 (default, Sep 5 2011, 21:17:14) >> [GCC 4.6.1] on linux2 >> Type "help", "copyright", "credits" or "license" for more information. >> >>> from django.utils.functional import SimpleLazyObject >> >>> fake_bool = SimpleLazyObject(lambda : True) >> >>> fake_bool.__class__ >> <class 'django.utils.functional.SimpleLazyObject'> >> >>> fake_bool.__dict__ >> { >> '_setupfunc': <function <lambda> at 0x1c36ea8>, >> '_wrapped': <object object at 0x1d88b70> >> } >> >>> SimpleLazyObject.__dict__ >> dict_proxy({ >> '__module__': 'django.utils.functional', >> '__nonzero__': <function inner at 0x1f56490>, >> '__deepcopy__': <function __deepcopy__ at 0x1f562f8>, >> '__str__': <function inner at 0x1f561e8>, >> '_setup': <function _setup at 0x1f56160>, >> '__hash__': <function inner at 0x1f56408>, >> '__unicode__': <function inner at 0x1f56270>, >> '__bool__': <function inner at 0x1f56490>, >> '__eq__': <function inner at 0x1f56380>, >> '__doc__': '\n A lazy object initialised from any function.\n\n >> Designed for compound objects of unknown type. For builtins or >> objects of\n known type, use django.utils.functional.lazy.\n ', >> '__init__': <function __init__ at 0x1f560d8> >> }) >> -------------------------------------------------------------------------- >> >> In Python 3, there's no __class__ property as there is in Python 2, >> the fake_bool's type isn't bool, and the callable to set up the wrapped >> object never gets called (which is why _wrapped is not set to True, but to >> an anonymous object - this is set in SimpleLazyObject.__init__). >> > > The Python compiler can do strange things with assignment to __class__ in > the presence of super. This issue has now been fixed, but it may be what is > biting you: > > http://bugs.python.org/issue12370 > > If this *is* the problem, then see the workaround suggested in the issue. > (alias super to _super in the module scope and use the old style super > calling convention.) > > Michael > > >> >> Puzzling! >> >> Regards, >> >> Vinay Sajip >> >> _______________________________________________ >> 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/fuzzyman%40voidspace.org.uk >> > > > > -- > > http://www.voidspace.org.uk/ > > May you do good and not evil > May you find forgiveness for yourself and forgive others > > May you share freely, never taking more than you give. > -- the sqlite blessing http://www.sqlite.org/different.html > > _______________________________________________ > 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/guido%40python.org > > -- --Guido van Rossum (python.org/~guido) _______________________________________________ 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
