qiskit/converters/ast_to_dag.py
def _process_node(self, node):
        """Carry out the action associated with a node."""
        if node.type == "program":
            self._process_children(node)

        elif node.type == "qreg":
            qreg = QuantumRegister(node.index, node.name)
            self.dag.add_qreg(qreg)

        elif node.type == "creg":
            creg = ClassicalRegister(node.index, node.name)
            self.dag.add_creg(creg)

        elif node.type == "id":
            raise QiskitError("internal error: _process_node on id")

        elif node.type == "int":
            raise QiskitError("internal error: _process_node on int")

        elif node.type == "real":
            raise QiskitError("internal error: _process_node on real")

        elif node.type == "indexed_id":
            raise QiskitError("internal error: _process_node on indexed_id")

        elif node.type == "id_list":
            # We process id_list nodes when they are leaves of barriers.
            return [self._process_bit_id(node_children)
                    for node_children in node.children]

        elif node.type == "primary_list":
            # We should only be called for a barrier.
            return [self._process_bit_id(m) for m in node.children]

        elif node.type == "gate":
            self._process_gate(node)

        elif node.type == "custom_unitary":
            self._process_custom_unitary(node)

        elif node.type == "universal_unitary":
            args = self._process_node(node.children[0])
            qid = self._process_bit_id(node.children[1])
            for element in qid:
                self.dag.apply_operation_back(UBase(*args, element), self.condition)

        elif node.type == "cnot":
            self._process_cnot(node)

        elif node.type == "expression_list":
            return node.children

        elif node.type == "binop":
            raise QiskitError("internal error: _process_node on binop")

        elif node.type == "prefix":
            raise QiskitError("internal error: _process_node on prefix")

        elif node.type == "measure":
            self._process_measure(node)

        elif node.type == "format":
            self.version = node.version()

        elif node.type == "barrier":
            ids = self._process_node(node.children[0])
            qubits = []
            for qubit in ids:
                for j, _ in enumerate(qubit):
                    qubits.append(qubit[j])
            self.dag.apply_operation_back(Barrier(len(qubits)), qubits, [])

        elif node.type == "reset":
            id0 = self._process_bit_id(node.children[0])
            for i, _ in enumerate(id0):
                self.dag.apply_operation_back(Reset(), [id0[i]], [], self.condition)

        elif node.type == "if":
            self._process_if(node)

        elif node.type == "opaque":
            self._process_gate(node, opaque=True)

        elif node.type == "external":
            raise QiskitError("internal error: _process_node on external")

        else:
            raise QiskitError("internal error: undefined node type",
                              node.type, "line=%s" % node.line,
                              "file=%s" % node.file)
        return None
def _process_node(self, node):
        """Carry out the action associated with a node."""
        if node.type == "program":
            self._process_children(node)

        elif node.type == "qreg":
            qreg = QuantumRegister(node.index, node.name)
            self.dag.add_qreg(qreg)

        elif node.type == "creg":
            creg = ClassicalRegister(node.index, node.name)
            self.dag.add_creg(creg)

        elif node.type == "id":
            raise QiskitError("internal error: _process_node on id")

        elif node.type == "int":
            raise QiskitError("internal error: _process_node on int")

        elif node.type == "real":
            raise QiskitError("internal error: _process_node on real")

        elif node.type == "indexed_id":
            raise QiskitError("internal error: _process_node on indexed_id")

        elif node.type == "id_list":
            # We process id_list nodes when they are leaves of barriers.
            return [self._process_bit_id(node_children)
                    for node_children in node.children]

        elif node.type == "primary_list":
            # We should only be called for a barrier.
            return [self._process_bit_id(m) for m in node.children]

        elif node.type == "gate":
            self._process_gate(node)

        elif node.type == "custom_unitary":
            self._process_custom_unitary(node)

        elif node.type == "universal_unitary":
            args = self._process_node(node.children[0])
            qid = self._process_bit_id(node.children[1])
            for element in qid:
                self.dag.apply_operation_back(UBase(*args, element), self.condition)

        elif node.type == "cnot":
            self._process_cnot(node)

        elif node.type == "expression_list":
            return node.children

        elif node.type == "binop":
            raise QiskitError("internal error: _process_node on binop")

        elif node.type == "prefix":
            raise QiskitError("internal error: _process_node on prefix")

        elif node.type == "measure":
            self._process_measure(node)

        elif node.type == "format":
            self.version = node.version()

        elif node.type == "barrier":
            ids = self._process_node(node.children[0])
            qubits = []
            for qubit in ids:
                for j, _ in enumerate(qubit):
                    qubits.append(qubit[j])
            self.dag.apply_operation_back(Barrier(len(qubits)), qubits, [])

        elif node.type == "reset":
            id0 = self._process_bit_id(node.children[0])
            for i, _ in enumerate(id0):
                self.dag.apply_operation_back(Reset(), [id0[i]], [], self.condition)

        elif node.type == "if":
            self._process_if(node)

        elif node.type == "opaque":
            self._process_gate(node, opaque=True)

        elif node.type == "external":
            raise QiskitError("internal error: _process_node on external")

        else:
            raise QiskitError("internal error: undefined node type",
                              node.type, "line=%s" % node.line,
                              "file=%s" % node.file)
        return None
Carry out the action associated with a node.