'Backend index for PyECLib
:param node_index: integer of node index
:return: integer of actual fragment index. if param is not an integer,
return None instead'

def get_backend_index(self, node_index):

    try:
        node_index = int(node_index)
    except ValueError:
        return None
    return (node_index % self.ec_n_unique_fragments)
