Simple example of metaclass usage in Python

meta_2.py

" Python 2 version "

class MyMetaclass(type): 

    def __new__(cls, name, bases, dct):

        attrs = ((name, value) for name, value in dct.items() if not name.startswith('__'))
        attrs = dict(("__" + name.upper(), value) for name, value in attrs)

        return super(MyMetaclass, cls).__new__(cls, name, bases, attrs)


class BaseClass(object):
    __metaclass__ = MyMetaclass

class Banana(BaseClass):
    v = 10


if __name__ == '__main__':

    kk = Banana()

    try:
        print "kk.v is: %s" % kk.v
    except AttributeError:
        print "There is not a 'kk.v' here"

meta_3.py

" Python 3 version "

class MyMetaclass(type): 

    def __new__(cls, name, bases, dct):

        attrs = ((name, value) for name, value in dct.items() if not name.startswith('__'))
        attrs = dict(("__" + name.upper(), value) for name, value in attrs)

        return super(MyMetaclass, cls).__new__(cls, name, bases, attrs)


class BaseClass(object, metaclass=MyMetaclass):
    pass

class Banana(BaseClass):
    v = 10


if __name__ == '__main__':

    kk = Banana()

    try:
        print("kk.v is: ",kk.v)
    except AttributeError:
        print("There is not a 'kk.v' here")