NodeMixin - TypeError: multiple bases have instance lay-out conflict

[bakert]

Works: 2.4.3
Breaks: 2.6.0

>>> from munch import Munch
>>> from anytree import NodeMixin
>>> class MyClass(Munch, NodeMixin):
...     pass
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: multiple bases have instance lay-out conflict

Where munch is https://github.com/Infinidat/munch

Googling around a bit this seems to be about conflicts in C implementations of classes on __foo__ attributes. So I did this:

>>> [k for k in dir(Munch) if k in dir(NodeMixin)]
['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']

but it didn't make me feel much smarter.

Does this mean anything to you anytree peeps? I came here because obviously NodeMixin is meant to be mixed in so this feels like a bug rather than just a stupid thing I should not be attempting to do. Especially as it used to work until this version.

[bakert]

The Munch folks believe that it's probably because Munch derives from dict which uses __slots__. Does NodeMixin now use __slots__?

[c0fec0de]

Yes. __slots__ has been added. Please try:

>>> from munch import Munch
>>> from anytree import NodeMixin
>>> class MyNodeMixin(NodeMixin):
...     pass
>>> class MyClass(Munch, MyNodeMixin):
...     pass

As __slots__ is not inherited, it might work

[bakert]

Thanks for taking a look. Sadly the above code gives the same error.

[gaghalfrunt pd] python3
Python 3.7.1 (default, Nov 28 2018, 11:51:47) 
[Clang 10.0.0 (clang-1000.11.45.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from munch import Munch
>>> from anytree import NodeMixin
>>> class MyNodeMixin(NodeMixin):
...     pass
... 
>>> class MyClass(Munch, MyNodeMixin):
...     pass
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: multiple bases have instance lay-out conflict

[bakert]

Reading up at https://stackoverflow.com/questions/472000/usage-of-slots and https://docs.python.org/3/reference/datamodel.html#notes-on-using-slots it sounds like including __slots__ in something designed to be inherited from/mixed in might be something you want to revisit? I'm a total ignoramus so I'm all ears if you have any ideas other than freezing the anytree version at 2.4.3. Thanks!

[jkbgbr]

I had the same exception the other day when I tried to mix wxPython and the NodeMixin class. Did not really expect it to work anyway, as wxPython heavily uses the attribute name parent.

…

On Wed, Feb 20, 2019 at 5:15 PM Thomas David Baker ***@***.***> wrote: Reading up at https://stackoverflow.com/questions/472000/usage-of-slots and https://docs.python.org/3/reference/datamodel.html#notes-on-using-slots it sounds like including __slots__ in something designed to be inherited from/mixed in might be something you want to revisit? I'm a total ignoramus so I'm all ears if you have any ideas other than freezing the anytree version at 2.4.3. Thanks! — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#77 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AFkmCtntGITKeg23zUarK0PgTcmeXIIxks5vPXS8gaJpZM4a_Wyo> .

[c0fec0de]

I am not sure yet, which is the best way to go. Leave __slots__ or remove.

[c0fec0de]

slots will be removed