'Called by the CollectorIterator object to retrieve the
result\'s values one after another (order defined by the
implementation)
\param idx The index of the result we want, wrt collector\'s order
\param timeout integer telling how long to wait (in seconds)
for the result at index idx to be available, or None (wait
forever)'

def _get_result(self, idx, timeout=None):

    raise NotImplementedError('Children    classes    must    implement    it')
