metaclass multiple inheritance inconsistency
- by Matt Anderson
Why is this:
class MyType(type):
def __init__(cls, name, bases, attrs):
print 'created', cls
class MyMixin:
__metaclass__ = MyType
class MyList(list, MyMixin): pass
okay, and works as expected:
created <class '__main__.MyMixin'>
created <class '__main__.MyList'>
But this:
class MyType(type):
def __init__(cls, name, bases, attrs):
print 'created', cls
class MyMixin:
__metaclass__ = MyType
class MyObject(object, MyMixin): pass
Is not okay, and blows up thusly?:
created <class '__main__.MyMixin'>
Traceback (most recent call last):
File "/tmp/junk.py", line 11, in <module>
class MyObject(object, MyMixin): pass
TypeError: Error when calling the metaclass bases
Cannot create a consistent method resolution
order (MRO) for bases object, MyMixin
