qiskit/dagcircuit/dagcircuit.py
def multigraph_layers(self):
        """Yield layers of the multigraph."""
        predecessor_count = dict()  # Dict[node, predecessors not visited]
        cur_layer = [node for node in self.input_map.values()]
        yield cur_layer
        next_layer = []
        while cur_layer:
            for node in cur_layer:
                # Count multiedges with multiplicity.
                for successor in self._multi_graph.successors(node):
                    multiplicity = self._multi_graph.number_of_edges(node, successor)
                    if successor in predecessor_count:
                        predecessor_count[successor] -= multiplicity
                    else:
                        predecessor_count[successor] = \
                            self._multi_graph.in_degree(successor) - multiplicity

                    if predecessor_count[successor] == 0:
                        next_layer.append(successor)
                        del predecessor_count[successor]

            yield next_layer
            cur_layer = next_layer
            next_layer = []
def multigraph_layers(self):
        """Yield layers of the multigraph."""
        predecessor_count = dict()  # Dict[node, predecessors not visited]
        cur_layer = [node for node in self.input_map.values()]
        yield cur_layer
        next_layer = []
        while cur_layer:
            for node in cur_layer:
                # Count multiedges with multiplicity.
                for successor in self._multi_graph.successors(node):
                    multiplicity = self._multi_graph.number_of_edges(node, successor)
                    if successor in predecessor_count:
                        predecessor_count[successor] -= multiplicity
                    else:
                        predecessor_count[successor] = \
                            self._multi_graph.in_degree(successor) - multiplicity

                    if predecessor_count[successor] == 0:
                        next_layer.append(successor)
                        del predecessor_count[successor]

            yield next_layer
            cur_layer = next_layer
            next_layer = []
Yield layers of the multigraph.