backend.target_history() caches backend properties

[jyu00]

Describe the bug

backend.target_history() calls _get_properties():

qiskit-ibm-runtime/qiskit_ibm_runtime/ibm_backend.py

Lines 349 to 355 in 51d897b

	def target_history(self, datetime: Optional[python_datetime] = None) -> Target:
	"""A :class:`qiskit.transpiler.Target` object for the backend.
	Returns:
	Target with properties found on `datetime`
	"""
	self._get_properties(datetime=datetime)

which saves the properties of that given timestamp as _properties:

qiskit-ibm-runtime/qiskit_ibm_runtime/ibm_backend.py

Lines 241 to 249 in 51d897b

	def _get_properties(self, datetime: Optional[python_datetime] = None) -> None:
	"""Gets backend properties and decodes it"""
	if datetime:
	datetime = local_to_utc(datetime)
	if datetime or not self._properties:
	api_properties = self._api_client.backend_properties(self.name, datetime=datetime)
	if api_properties:
	backend_properties = properties_from_server_data(api_properties)
	self._properties = backend_properties

which means if I do

old_history = backend.target_history(datetime=<1 year ago>)
props = backend.properties()

I'll actually get old_history back in my second call.

Steps to reproduce

Expected behavior

Historical properties should not be cached. backend.properties() does this correctly.

Suggested solutions

Don't cache properties if datetime is provided.

Additional Information

• qiskit-ibm-runtime version:
• Python version:
• Operating system:

[kt474]

Should the target also not be cached when calling target_history()? Currently, calling backend.target after backend.target_history() would still return the old target.

[jyu00]

Should the target also not be cached when calling target_history()? Currently, calling backend.target after backend.target_history() would still return the old target.

Right. Backend properties should not be cached if an older copy is requested.