Layout.get_registers() does not return registers

[itoko]

Information

• Qiskit Terra version: 0.8.0
• Python version: 3.6
• Operating system: Mac

What is the current behavior?

Layout.get_registers() returns (virtual) qubits:

return list(self.get_virtual_bits().keys())

What is the expected behavior?

Layout.get_registers() returns (virtual quantum) registers:

return set([reg for reg, idx in self.get_virtual_bits().keys()])

Suggested solutions

Change the implementation of Layout.get_registers() to:

return set([reg for reg, idx in self.get_virtual_bits().keys()])

Change the line in BasicSwap.run()

                        for qreg in current_layout.get_registers():
                            if qreg[0] not in swap_layer.qregs.values():
                                swap_layer.add_qreg(qreg[0])

to

                        for qreg in current_layout.get_registers():
                            if qreg not in swap_layer.qregs.values():
                                swap_layer.add_qreg(qreg)