qiskit.dagcircuit.DAGCircuit

__init__()

Create an empty circuit.

add_creg(creg)

Add all wires in a classical register.

add_qreg(qreg)

Add all wires in a quantum register.

ancestors(node)

Returns set of the ancestors of a node as DAGNodes.

apply_operation_back(op, qargs=None, cargs=None, condition=None)

Apply an operation to the output of the circuit.

Parameters

• op (qiskit.circuit.Instruction) – the operation associated with the DAG node
• qargs (list[Qubit]) – qubits that op will be applied to
• cargs (list[Clbit]) – cbits that op will be applied to
• condition (tuple or None) – DEPRACTED optional condition (ClassicalRegister, int)

Returns

the current max node

Return type

DAGNode

Raises

DAGCircuitError – if a leaf node is connected to multiple outputs

apply_operation_front(op, qargs, cargs, condition=None)

Apply an operation to the input of the circuit.

Parameters

• op (qiskit.circuit.Instruction) – the operation associated with the DAG node
• qargs (list[Qubit]) – qubits that op will be applied to
• cargs (list[Clbit]) – cbits that op will be applied to
• condition (tuple or None) – DEPRACTED optional condition (ClassicalRegister, int)

Returns

the current max node

Return type

DAGNode

Raises

DAGCircuitError – if initial nodes connected to multiple out edges

bfs_successors(node)

Returns an iterator of tuples of (DAGNode, [DAGNodes]) where the DAGNode is the current node and [DAGNode] is its successors in BFS order.

Return calibration dictionary.

The custom pulse definition of a given gate is of the form

{‘gate_name’: {(qubits, params): schedule}}

Return a list of classical bits (as a list of Clbit instances).

collect_runs(namelist)

Return a set of non-conditional runs of “op” nodes with the given names.

For example, “… h q[0]; cx q[0],q[1]; cx q[0],q[1]; h q[1]; ..” would produce the tuple of cx nodes as an element of the set returned from a call to collect_runs([“cx”]). If instead the cx nodes were “cx q[0],q[1]; cx q[1],q[0];”, the method would still return the pair in a tuple. The namelist can contain names that are not in the circuit’s basis.

Nodes must have only one successor to continue the run.

compose(other, edge_map=None, qubits=None, clbits=None, front=False, inplace=True)

Compose the other circuit onto the output of this circuit.

A subset of input wires of other are mapped to a subset of output wires of this circuit.

other can be narrower or of equal width to self.

Parameters

• other (DAGCircuit) – circuit to compose with self
• edge_map (dict) – DEPRECATED - a {Bit: Bit} map from input wires of other to output wires of self (i.e. rhs->lhs). The key, value pairs can be either Qubit or Clbit mappings.
• qubits (list[Qubit|int]) – qubits of self to compose onto.
• clbits (list[Clbit|int]) – clbits of self to compose onto.
• front (bool) – If True, front composition will be performed (not implemented yet)
• inplace (bool) – If True, modify the object. Otherwise return composed circuit.

Returns

the composed dag (returns None if inplace==True).

Return type

DAGCircuit

Raises

DAGCircuitError – if other is wider or there are duplicate edge mappings.

compose_back(input_circuit, edge_map=None)

DEPRECATED: use DAGCircuit.compose() instead.

count_ops()

Count the occurrences of operation names.

Returns a dictionary of counts keyed on the operation name.

count_ops_longest_path()

Count the occurrences of operation names on the longest path.

Returns a dictionary of counts keyed on the operation name.

depth()

Return the circuit depth. :returns: the circuit depth :rtype: int

Raises

DAGCircuitError – if not a directed acyclic graph

descendants(node)

Returns set of the descendants of a node as DAGNodes.

draw(scale=0.7, filename=None, style='color')

Draws the dag circuit.

This function needs pydot, which in turn needs Graphviz to be installed.

Parameters

• scale (float) – scaling factor
• filename (str) – file path to save image to (format inferred from name)
• style (str) – ‘plain’: B&W graph; ‘color’ (default): color input/output/op nodes

Returns

if in Jupyter notebook and not saving to file, otherwise None.

Return type

Ipython.display.Image

edges(nodes=None)

Iterator for edge values and source and dest node

This works by returning the output edges from the specified nodes. If no nodes are specified all edges from the graph are returned.

Parameters

nodes (DAGNode|list(DAGNode) – Either a list of nodes or a single input node. If none is specified all edges are returned from the graph.

Yields

edge –

the edge in the same format as out_edges the tuple

(source node, destination node, edge data)

extend_back(dag, edge_map=None)

DEPRECATED: Add dag at the end of self, using edge_map.

classmethod from_networkx(graph)

Take a networkx MultiDigraph and create a new DAGCircuit.

Parameters

graph (networkx.MultiDiGraph) – The graph to create a DAGCircuit object from. The format of this MultiDiGraph format must be in the same format as returned by to_networkx.

Returns

The dagcircuit object created from the networkx

MultiDiGraph.

Return type

DAGCircuit

front_layer()

Return a list of op nodes in the first layer of this dag.

gate_nodes()

Get the list of gate nodes in the dag.

Returns

the list of DAGNodes that represent gates.

Return type

list[DAGNode]

Return the global phase of the circuit.

has_calibration_for(node)

Return True if the dag has a calibration defined for the node operation. In this case, the operation does not need to be translated to the device basis.

idle_wires(ignore=None)

Return idle wires.

Parameters

ignore (list(str)) – List of node names to ignore. Default: []

Yields

Bit – Bit in idle wire.

layers()

Yield a shallow view on a layer of this DAGCircuit for all d layers of this circuit.

A layer is a circuit whose gates act on disjoint qubits, i.e., a layer has depth 1. The total number of layers equals the circuit depth d. The layers are indexed from 0 to d-1 with the earliest layer at index 0. The layers are constructed using a greedy algorithm. Each returned layer is a dict containing {“graph”: circuit graph, “partition”: list of qubit lists}.

The returned layer contains new (but semantically equivalent) DAGNodes. These are not the same as nodes of the original dag, but are equivalent via DAGNode.semantic_eq(node1, node2).

TODO: Gates that use the same cbits will end up in different layers as this is currently implemented. This may not be the desired behavior.

longest_path()

Returns the longest path in the dag as a list of DAGNodes.

multi_qubit_ops()

Get list of 3+ qubit operations. Ignore directives like snapshot and barrier.

multigraph_layers()

Yield layers of the multigraph.

named_nodes(*names)

Get the set of “op” nodes with the given name.

node(node_id)

Get the node in the dag.

Parameters

node_id (int) – Node identifier.

Returns

the node.

Return type

node

Returns the number of nodes in the dag.

nodes()

Iterator for node values.

Yields

node – the node.

nodes_on_wire(wire, only_ops=False)

Iterator for nodes that affect a given wire.

Parameters

• wire (Bit) – the wire to be looked at.
• only_ops (bool) – True if only the ops nodes are wanted; otherwise, all nodes are returned.

Yields

DAGNode – the successive ops on the given wire

Raises

DAGCircuitError – if the given wire doesn’t exist in the DAG

num_clbits()

Return the total number of classical bits used by the circuit.

num_qubits()

Return the total number of qubits used by the circuit. num_qubits() replaces former use of width(). DAGCircuit.width() now returns qubits + clbits for consistency with Circuit.width() [qiskit-terra #2564].

num_tensor_factors()

Compute how many components the circuit can decompose into.

op_nodes(op=None, include_directives=True)

Get the list of “op” nodes in the dag.

Parameters

• op (Type) – qiskit.circuit.Instruction subclass op nodes to return. If None, return all op nodes.
• include_directives (bool) – include barrier, snapshot etc.

Returns

the list of node ids containing the given op.

Return type

list[DAGNode]

predecessors(node)

Returns iterator of the predecessors of a node as DAGNodes.

properties()

Return a dictionary of circuit properties.

quantum_predecessors(node)

Returns iterator of the predecessors of a node that are connected by a quantum edge as DAGNodes.

quantum_successors(node)

Returns iterator of the successors of a node that are connected by a quantum edge as DAGNodes.

Return a list of qubits (as a list of Qubit instances).

remove_all_ops_named(opname)

Remove all operation nodes with the given name.

remove_ancestors_of(node)

Remove all of the ancestor operation nodes of node.

remove_descendants_of(node)

Remove all of the descendant operation nodes of node.

remove_nonancestors_of(node)

Remove all of the non-ancestors operation nodes of node.

remove_nondescendants_of(node)

Remove all of the non-descendants operation nodes of node.

remove_op_node(node)

Remove an operation node n.

Add edges from predecessors to successors.

reverse_ops()

Reverse the operations in the self circuit.

Returns

the reversed dag.

Return type

DAGCircuit

serial_layers()

Yield a layer for all gates of this circuit.

A serial layer is a circuit with one gate. The layers have the same structure as in layers().

size()

Return the number of operations.

substitute_node(node, op, inplace=False)

Replace a DAGNode with a single instruction. qargs, cargs and conditions for the new instruction will be inferred from the node to be replaced. The new instruction will be checked to match the shape of the replaced instruction.

Parameters

• node (DAGNode) – Node to be replaced
• op (qiskit.circuit.Instruction) – The qiskit.circuit.Instruction instance to be added to the DAG
• inplace (bool) – Optional, default False. If True, existing DAG node will be modified to include op. Otherwise, a new DAG node will be used.

Returns

the new node containing the added instruction.

Return type

DAGNode

Raises

• DAGCircuitError – If replacement instruction was incompatible with
• location of target node. –

substitute_node_with_dag(node, input_dag, wires=None)

Replace one node with dag.

Parameters

• node (DAGNode) – node to substitute
• input_dag (DAGCircuit) – circuit that will substitute the node
• wires (list[Bit]) – gives an order for (qu)bits in the input circuit. This order gets matched to the node wires by qargs first, then cargs, then conditions.

Raises

DAGCircuitError – if met with unexpected predecessor/successors

successors(node)

Returns iterator of the successors of a node as DAGNodes.

threeQ_or_more_gates()

Get list of 3-or-more-qubit gates: (id, data).

to_networkx()

Returns a copy of the DAGCircuit in networkx format.

topological_nodes()

Yield nodes in topological order.

Returns

node in topological order

Return type

generator(DAGNode)

topological_op_nodes()

Yield op nodes in topological order.

Returns

op node in topological order

Return type

generator(DAGNode)

twoQ_gates()

Get list of 2-qubit gates. Ignore snapshot, barriers, and the like.

two_qubit_ops()

Get list of 2 qubit operations. Ignore directives like snapshot and barrier.

width()

Return the total number of qubits + clbits used by the circuit. This function formerly returned the number of qubits by the calculation return len(self._wires) - self.num_clbits() but was changed by issue #2564 to return number of qubits + clbits with the new function DAGCircuit.num_qubits replacing the former semantic of DAGCircuit.width().

Return a list of the wires in order.