Problems with subclassing enum34
trying out the enum34 module. What I want to create is a subclass of enum.Enum that is also based on ctypes.c_int so that I can better use enum instances in ctypes api calls. When I do this, I get a metaclass conflict: class MyEnum(ctypes.c_int, enum.Enum): ...FOOBAR = 0 ... Traceback (most recent call last): File stdin, line 1, in module TypeError: Error when calling the metaclass bases metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases When I do this, it does not work either: class MyEnum_meta(type(ctypes.c_int), type(enum.Enum)): ... pass ... class MyEnum(ctypes.c_int, enum.Enum): ... FOOBAR = 42 ... __metaclass__ = MyEnum_meta ... MyEnum.FOOBAR 42 It should have printed 'MyEnum.FOOBAR: 42'. Any ideas? Thanks, Thomas -- http://mail.python.org/mailman/listinfo/python-list
Re: Problems with subclassing enum34
On 2013-06-28 11:48, Thomas Heller wrote: trying out the enum34 module. What I want to create is a subclass of enum.Enum that is also based on ctypes.c_int so that I can better use enum instances in ctypes api calls. When I do this, I get a metaclass conflict: class MyEnum(ctypes.c_int, enum.Enum): ...FOOBAR = 0 ... Traceback (most recent call last): File stdin, line 1, in module TypeError: Error when calling the metaclass bases metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases When I do this, it does not work either: class MyEnum_meta(type(ctypes.c_int), type(enum.Enum)): ... pass enum.EnumMeta uses super() in its __new__() implementation but _ctypes.PyCSimpleType doesn't. Thus, only _ctypes.PyCSimpleType.__new__() gets a chance to run. Switching the order of the two might work. -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
Re: Problems with subclassing enum34
Thomas Heller於 2013年6月28日星期五UTC+8下午6時48分38秒寫道： trying out the enum34 module. What I want to create is a subclass of enum.Enum that is also based on ctypes.c_int so that I can better use enum instances in ctypes api calls. When I do this, I get a metaclass conflict: class MyEnum(ctypes.c_int, enum.Enum): ...FOOBAR = 0 ... Traceback (most recent call last): File stdin, line 1, in module TypeError: Error when calling the metaclass bases metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases When I do this, it does not work either: class MyEnum_meta(type(ctypes.c_int), type(enum.Enum)): ... pass ... class MyEnum(ctypes.c_int, enum.Enum): ... FOOBAR = 42 ... __metaclass__ = MyEnum_meta ... MyEnum.FOOBAR 42 It should have printed 'MyEnum.FOOBAR: 42'. Any ideas? Thanks, Thomas Just use a dictionary for the job. Python i not c/c++. -- http://mail.python.org/mailman/listinfo/python-list
Re: Problems with subclassing enum34
On 06/28/2013 03:48 AM, Thomas Heller wrote: trying out the enum34 module. What I want to create is a subclass of enum.Enum that is also based on ctypes.c_int so that I can better use enum instances in ctypes api calls. Have you tried using enum.IntEnum? If you were able to pass ints in before, IntEnum should work. -- ~Ethan~ -- http://mail.python.org/mailman/listinfo/python-list
Re: Problems with subclassing enum34
Am 28.06.2013 17:16, schrieb Ethan Furman: On 06/28/2013 03:48 AM, Thomas Heller wrote: trying out the enum34 module. What I want to create is a subclass of enum.Enum that is also based on ctypes.c_int so that I can better use enum instances in ctypes api calls. Have you tried using enum.IntEnum? If you were able to pass ints in before, IntEnum should work. I'm sure that IntEnum works as expected, but I need enums that are subclasses of ctypes.c_int (so that argument type checking and return value conversions in ctypes api calls work). Robert Kern: enum.EnumMeta uses super() in its __new__() implementation but _ctypes.PyCSimpleType doesn't. Thus, only _ctypes.PyCSimpleType.__new__() gets a chance to run. Switching the order of the two might work. Robert found the problem but I'm unsure if there is a solution. Also I'm unsure whether this is a bug in ctypes or in enum or if they are simply incompatible. Thomas -- http://mail.python.org/mailman/listinfo/python-list
Re: Problems with subclassing enum34
Am 28.06.2013 17:25, schrieb Thomas Heller: Robert Kern: enum.EnumMeta uses super() in its __new__() implementation but _ctypes.PyCSimpleType doesn't. Thus, only _ctypes.PyCSimpleType.__new__() gets a chance to run. Switching the order of the two might work. Robert found the problem but I'm unsure if there is a solution. Also I'm unsure whether this is a bug in ctypes or in enum or if they are simply incompatible. I forgot to mention that switching the order of metaclasses didn't work. Thomas -- http://mail.python.org/mailman/listinfo/python-list
Re: Problems with subclassing enum34
On 2013-06-28 16:32, Thomas Heller wrote: Am 28.06.2013 17:25, schrieb Thomas Heller: Robert Kern: enum.EnumMeta uses super() in its __new__() implementation but _ctypes.PyCSimpleType doesn't. Thus, only _ctypes.PyCSimpleType.__new__() gets a chance to run. Switching the order of the two might work. Robert found the problem but I'm unsure if there is a solution. Also I'm unsure whether this is a bug in ctypes or in enum or if they are simply incompatible. I forgot to mention that switching the order of metaclasses didn't work. You may also need to manually deal with the conflict between Enum.__new__() and c_int.__new__(). -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
Re: Problems with subclassing enum34
On 06/28/2013 08:32 AM, Thomas Heller wrote: Am 28.06.2013 17:25, schrieb Thomas Heller: Robert Kern: enum.EnumMeta uses super() in its __new__() implementation but _ctypes.PyCSimpleType doesn't. Thus, only _ctypes.PyCSimpleType.__new__() gets a chance to run. Switching the order of the two might work. Robert found the problem but I'm unsure if there is a solution. Also I'm unsure whether this is a bug in ctypes or in enum or if they are simply incompatible. I forgot to mention that switching the order of metaclasses didn't work. Here's the traceback: Traceback (most recent call last): File ct.py, line 7, in module class MyEnum(ctypes.c_int, Enum): File /home/ethan/source/enum/enum/py2_enum.py, line 149, in __new__ enum_class = super(EnumMeta, metacls).__new__(metacls, cls, bases, classdict) TypeError: Error when calling the metaclass bases _ctypes.PyCSimpleType.__new__(MyEnum_meta) is not safe, use type.__new__() Not sure how to fix that. -- ~Ethan~ -- http://mail.python.org/mailman/listinfo/python-list
