Resolving metaclass conflicts

Question

I need to create a class that uses a different base class depending on some condition. With some classes I get the infamous:

TypeError: metaclass conflict: t         


        

Answer 1

Your example using sqlite3 is invalid because it is a module and not a class. I have also encountered this issue.

Heres your problem: The base class has a metaclass that is not the same type as the subclass. That is why you get a TypeError.

I used a variation of this activestate snippet using noconflict.py. The snippet needs to be reworked as it is not python 3.x compatible. Regardless, it should give you a general idea.

Problem snippet

class M_A(type):
    pass
class M_B(type):
    pass
class A(object):
    __metaclass__=M_A
class B(object):
    __metaclass__=M_B
class C(A,B):
    pass

#Traceback (most recent call last):
#  File "", line 1, in ?
#TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass #of the metaclasses of all its bases

Solution snippet

from noconflict import classmaker
class C(A,B):
    __metaclass__=classmaker()

print C
#

The code recipe properly resolves the metaclasses for you.