Unable to deepcopy an IBMBackend

[cyberteej]

Describe the bug

With the old IBMQBackends, deepcopying was allowed. With the new IBMBackends, it results in a recursion error. Loosely, this seems to be because deepcopy checks if _properties is an attribute of IBMBackend (when it is constructing the new, empty IBMBackend), and the __getattr__ function of IBMBackend calls self._get_properties() internally, resulting in an infinite loop of trying to access the attribute _properties which doesn't exist yet. This is also true for _defaults and _configuration.

I'm open to the idea that deepcopying backends should be discouraged for some reason but feel like at least the error should be improved.

Steps to reproduce

from qiskit_ibm_runtime import QiskitRuntimeService
import copy

service = QiskitRuntimeService()
backend = service.get_backend('ibm_perth')
backend_copy = copy.deepcopy(backend)

Expected behavior

A copy of the backend (preferable) or avoiding infinite recursion.

Suggested solutions

Currently, I modify __getattr__ in ibm_backend.py to the following, which is very hacky and I'm worried there's some edge case behaviour I may affect

   def __getattr__(self, name: str) -> Any:
        """Gets attribute from self or configuration

        This magic method executes when user accesses an attribute that
        does not yet exist on IBMBackend class.
        """
        # Lazy load properties and pulse defaults and construct the target object.
        if name not in ['_properties', '_defaults','_configuration']:
            self._get_properties()
            self._get_defaults()
            self._convert_to_target()
        # Check if the attribute now is available on IBMBackend class due to above steps
        try:
            return super().__getattribute__(name)
        except AttributeError:
            pass
        # If attribute is still not available on IBMBackend class,
        # fallback to check if the attribute is available in configuration
        if name not in ['_configuration']:
            try:
                return self._configuration.__getattribute__(name)
            except AttributeError:
                raise AttributeError(
                    "'{}' object has no attribute '{}'".format(
                        self.__class__.__name__, name
                    )
                )

Additional Information

• qiskit-ibm-runtime version: 0.10.0
• Python version: 3.8.8
• Operating system: macOS Ventura

[yaelbh]

This was fixed in qiskit-ibm-provider Qiskit/qiskit-ibm-provider#658