human
Complete this python program:
def _configure_subclass_mapper(mapper, context, path, adapter):
assistant
#Here is the Python program you requested.

    """Produce a mapper level row processor callable factory for mappers
    inheriting this one.
    """
    def configure_subclass_mapper(discriminator):
        try:
            sub_mapper = mapper.polymorphic_map[discriminator]
        except KeyError:
            raise AssertionError(('No    such    polymorphic_identity    %r    is    defined' % discriminator))
        if (sub_mapper is mapper):
            return None
        return instance_processor(sub_mapper, context, path, adapter, polymorphic_from=mapper)
    return configure_subclass_mapper