Python: make every instance have a different superclass

I could be wrong, but I don't think you want a metaclass here. __metaclass__es are used when the class is created, not when you call the class to construct a new instance of the class (or something else).

Here's an answer using __new__ without a metaclass. It feels a bit hacky, but it seems to work:

_sentinel = Ellipsis
class MyClass(object):
    def __new__(cls, name):
        if name is _sentinel:
            return object.__new__(cls)
        else:
            instance = type(name + cls.__name__, (MyClass,), {})(_sentinel)
            # Initialization goes here.
            return instance

print type(MyClass('name1'))
print type(MyClass('name2'))

There's a catch here -- All the business logic of initializing then new instance must be done in __new__. Since __new__ is returning a different type than the class it is bound to, __init__ won't get called.

Another option is to create a class factory:

class MyClass(object):
    pass

def class_factory(name):
    new_cls = type(name + MyClass.__name__, (MyClass,), {})
    return new_cls() # Or pass whatever you want in here...

print type(class_factory('name1'))
print type(class_factory('name2'))

Finally, you could even create a non-__new__ class method:

class MyClass(object):
    @classmethod
    def class_factory(cls, name):
        new_cls = type(name + cls.__name__, (cls,), {})
        return new_cls() # Or pass whatever you want in here...

print type(MyClass.class_factory('name1'))
print type(MyClass.class_factory('name2'))