Python 3 Patterns & Idioms / code / Metaclasses /

# Metaclasses/
# Emulating Java's 'final'

class final(type):
    def __init__(cls, name, bases, namespace):
        super(final, cls).__init__(name, bases, namespace)
        for klass in bases:
            if isinstance(klass, final):
                raise TypeError(str(klass.__name__) + " is final")

class A(object):

class B(A):
    __metaclass__= final

print B.__bases__
print isinstance(B, final)

# Produces compile-time error:
class C(B):

""" Output:
(<class '__main__.A'>,)
TypeError: B is final
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