Choosing a Metaclass?

[Jeff McNeil]

Hi list,

Hopefully a quick metaclass question. In the following example, MyMeta is a
metaclass that does not inherit directly from type:

#!/usr/bin/python

class MyMeta(object):
    def __new__(cls, name, bases, vars):
        print "MyMeta.__new__ called for %s" % name
        return type(name, bases, vars)

class MetaWrapper(object):
    __metaclass__ = MyMeta

class M(MetaWrapper):
    pass

[jeff at marvin ~]$ python t.py
MyMeta.__new__ called for MetaWrapper
[jeff at marvin ~]$

When I run that script, it's apparent that although M inherits from
MetaWrapper, it does not use MyMeta as it's metaclass.  However, if I change
MyMeta to be a subclass of builtin type, it works as I would expect:

[jeff at marvin ~]$ cat t.py
#!/usr/bin/python

class MyMeta(type):
    def __new__(cls, name, bases, vars):
        print "MyMeta.__new__ called for %s" % name
        return super(MyMeta, cls).__new__(cls, name, bases, vars)

class MetaWrapper(object):
    __metaclass__ = MyMeta

class M(MetaWrapper):
    pass

[jeff at marvin ~]$ python t.py
MyMeta.__new__ called for MetaWrapper
MyMeta.__new__ called for M
[jeff at marvin ~]$

How exactly does Python choose which MC it will use when building a class?
It doesn't seem to me that the parent class of MyMeta should matter in this
case?

Thanks!

Jeff
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