Read graph and add sequences to document

def _read_sequences(self, graph):
        """
        Read graph and add sequences to document
        """
        for e in self._get_elements(graph, SBOL.Sequence):
            identity = e[0]
            c = self._get_rdf_identified(graph, identity)
            c['elements'] = self._get_triplet_value(graph, identity, SBOL.elements)
            c['encoding'] = self._get_triplet_value(graph, identity, SBOL.encoding)
            seq = Sequence(**c)
            self._sequences[identity.toPython()] = seq
            self._collection_store[identity.toPython()] = seq