"metaclass conflict" error: where is noconflict ?

[Chris Rebert]

On Sun, Feb 22, 2009 at 3:31 AM, Barak, Ron <Ron.Barak at lsi.com> wrote:
<snip>
>> > Applying your suggestion:
>> >
>> > class ListControlMeta(type(wx.Frame), type(CopyAndPaste)):
>> >     pass
>> >
>> > class ListControl(wx.Frame, CopyAndPaste):
>> >     def __init__(self, parent, id, title, list, max_list_width,
>> > log_stream,
>> > style=wx.DEFAULT_FRAME_STYLE):
>> >
>> >         __metaclass__= ListControlMeta
>> >
>> >
>> > wx.Frame.__init__(self,parent,id,title,size=(max_list_width,-1),
>> > style=style)
>> >         self.list = list
>> >         self.log_stream = log_stream
>> >         self.list_ctrl = wx.ListCtrl(self, -1, style=wx.LC_REPORT |
>> > wx.LC_NO_HEADER)
>> >         self.list_ctrl.InsertColumn(0, title)
>> >         for i,line_ in enumerate(list):
>> >             self.list_ctrl.InsertStringItem(i, line_)
>> >                 ...
>> >
>> > I get:
>> >
>> > $ python -u ./failover_pickle_demo09.py Traceback (most recent call
>> > last):
>> >   File "./failover_pickle_demo09.py", line 319, in <module>
>> >     class ListControlMeta(type(wx.Frame), type(CopyAndPaste)):
>> > TypeError: Error when calling the metaclass bases
>> >     multiple bases have instance lay-out conflict
>>
>> >From what I recall, that basically means that type(wx.Frame) and
>> type(CopyAndPaste) are both C classes that are are mutually
>> incompatible. It's basically the same reason you can't
>> subclass from both `list` and `dict` or two other built-in
>> types (you get the exact same error).
>>
>> Sounds like the only way to workaround this would be to do
>> some coding in C or to use composition rather than
>> inheritance for one of ListControl's superclasses.
>
> The wx.Frame may be coded in C, but the CopyAndPaste class, which I wrote, is not (see it's listing below).
> Could you have a look at the CopyAndPaste class, and see if something in its construction strikes you as susspicious ?
>
> Thanks,
> Ron.
>
> $ cat ./CopyAndPaste.py
> #!/usr/bin/env python
>
> import wx
>
> class CopyAndPaste():

You need to subclass 'object' so as to make CopyAndPaste a new-style
class. This may or may not resolve the error, but you should be doing
it either way.

class CopyAndPaste(object):

Cheers,
Chris

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