Remove legacy providers interface (Qiskit/qiskit#7886)

* Remove legacy providers interface

This commit removes the legacy providers interface from terra. This
includes the BaseBackend, BaseJob, BaseProvider abstract classes and
everything that inherits from them in the tree. These classes were
deprecated as part of qiskit-terra 0.18.0 and have been supersceded by
the versioned provider interface and all providers should have migrated
by now to these new supported interface. This also means we no longer
support the qobj execution path and QuantumCircuit and Schedule objects
are used directly everywhere for running. In the future we can look at
deprecating and removing the assemble() function and qobj class in the
future as nothing in tree is using them directly. But before we can
deprecate these the IBM provider and aer will need to have native
implementations.

* Drop handling for incorrect backend.version in BaseBackend

Now that BaseBackend is no longer in qiskit we don't need to special
handle the case where backend.version is not the interface version
(since it was a method in BaseBackend). This commit drops the handling
for this and uses the interface for the versioned interface as it was
originally intended.

* Fix lint

* Fix typo causing test failures

The tests were failing because one of the default values for getting the
backend version attribute was None instead of 0 causing a type error
when an integer was expected. This was not caught previously because the
BaseBackend handling checked for non integer versions and converted
those to 0. However, now without BaseBackend we need to be more explicit
and use an integer for the backend interface version.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit_algorithms/amplitude_amplifiers/grover.py

@@ -19,7 +19,7 @@
 import numpy as np
 
 from qiskit import ClassicalRegister, QuantumCircuit
-from qiskit.providers import Backend, BaseBackend
+from qiskit.providers import Backend
 from qiskit.quantum_info import partial_trace
 from qiskit.utils import QuantumInstance
 from .amplification_problem import AmplificationProblem
@@ -112,7 +112,7 @@ def __init__(
         iterations: Optional[Union[List[int], Iterator[int], int]] = None,
         growth_rate: Optional[float] = None,
         sample_from_iterations: bool = False,
-        quantum_instance: Optional[Union[QuantumInstance, Backend, BaseBackend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
         r"""
         Args:
@@ -172,14 +172,12 @@ def quantum_instance(self) -> Optional[QuantumInstance]:
         return self._quantum_instance
 
     @quantum_instance.setter
-    def quantum_instance(
-        self, quantum_instance: Union[QuantumInstance, BaseBackend, Backend]
-    ) -> None:
+    def quantum_instance(self, quantum_instance: Union[QuantumInstance, Backend]) -> None:
         """Set quantum instance.
         Args:
             quantum_instance: The quantum instance used to run this algorithm.
         """
-        if isinstance(quantum_instance, (BaseBackend, Backend)):
+        if isinstance(quantum_instance, Backend):
             quantum_instance = QuantumInstance(quantum_instance)
         self._quantum_instance = quantum_instance
 

qiskit_algorithms/amplitude_estimators/ae.py

@@ -19,7 +19,7 @@
 from scipy.optimize import bisect
 
 from qiskit import QuantumCircuit, ClassicalRegister
-from qiskit.providers import BaseBackend, Backend
+from qiskit.providers import Backend
 from qiskit.utils import QuantumInstance
 from .amplitude_estimator import AmplitudeEstimator, AmplitudeEstimatorResult
 from .ae_utils import pdf_a, derivative_log_pdf_a, bisect_max
@@ -58,7 +58,7 @@ def __init__(
         num_eval_qubits: int,
         phase_estimation_circuit: Optional[QuantumCircuit] = None,
         iqft: Optional[QuantumCircuit] = None,
-        quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
         r"""
         Args:
@@ -98,15 +98,13 @@ def quantum_instance(self) -> Optional[QuantumInstance]:
         return self._quantum_instance
 
     @quantum_instance.setter
-    def quantum_instance(
-        self, quantum_instance: Union[QuantumInstance, BaseBackend, Backend]
-    ) -> None:
+    def quantum_instance(self, quantum_instance: Union[QuantumInstance, Backend]) -> None:
         """Set quantum instance.
 
         Args:
             quantum_instance: The quantum instance used to run this algorithm.
         """
-        if isinstance(quantum_instance, (BaseBackend, Backend)):
+        if isinstance(quantum_instance, Backend):
             quantum_instance = QuantumInstance(quantum_instance)
         self._quantum_instance = quantum_instance
 

qiskit_algorithms/amplitude_estimators/fae.py

@@ -16,7 +16,7 @@
 import numpy as np
 
 from qiskit.circuit import QuantumCircuit, ClassicalRegister
-from qiskit.providers import BaseBackend, Backend
+from qiskit.providers import Backend
 from qiskit.utils import QuantumInstance
 from qiskit.algorithms.exceptions import AlgorithmError
 
@@ -50,7 +50,7 @@ def __init__(
         delta: float,
         maxiter: int,
         rescale: bool = True,
-        quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
         r"""
         Args:
@@ -83,15 +83,13 @@ def quantum_instance(self) -> Optional[QuantumInstance]:
         return self._quantum_instance
 
     @quantum_instance.setter
-    def quantum_instance(
-        self, quantum_instance: Union[QuantumInstance, BaseBackend, Backend]
-    ) -> None:
+    def quantum_instance(self, quantum_instance: Union[QuantumInstance, Backend]) -> None:
         """Set quantum instance.
 
         Args:
             quantum_instance: The quantum instance used to run this algorithm.
         """
-        if isinstance(quantum_instance, (BaseBackend, Backend)):
+        if isinstance(quantum_instance, Backend):
             quantum_instance = QuantumInstance(quantum_instance)
         self._quantum_instance = quantum_instance
 

qiskit_algorithms/amplitude_estimators/iae.py

@@ -17,7 +17,7 @@
 from scipy.stats import beta
 
 from qiskit import ClassicalRegister, QuantumCircuit
-from qiskit.providers import BaseBackend, Backend
+from qiskit.providers import Backend
 from qiskit.utils import QuantumInstance
 
 from .amplitude_estimator import AmplitudeEstimator, AmplitudeEstimatorResult
@@ -52,7 +52,7 @@ def __init__(
         alpha: float,
         confint_method: str = "beta",
         min_ratio: float = 2,
-        quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
         r"""
         The output of the algorithm is an estimate for the amplitude `a`, that with at least
@@ -107,15 +107,13 @@ def quantum_instance(self) -> Optional[QuantumInstance]:
         return self._quantum_instance
 
     @quantum_instance.setter
-    def quantum_instance(
-        self, quantum_instance: Union[QuantumInstance, BaseBackend, Backend]
-    ) -> None:
+    def quantum_instance(self, quantum_instance: Union[QuantumInstance, Backend]) -> None:
         """Set quantum instance.
 
         Args:
             quantum_instance: The quantum instance used to run this algorithm.
         """
-        if isinstance(quantum_instance, (BaseBackend, Backend)):
+        if isinstance(quantum_instance, Backend):
             quantum_instance = QuantumInstance(quantum_instance)
         self._quantum_instance = quantum_instance
 

qiskit_algorithms/amplitude_estimators/mlae.py

@@ -17,7 +17,6 @@
 from scipy.optimize import brute
 from scipy.stats import norm, chi2
 
-from qiskit.providers import BaseBackend
 from qiskit.providers import Backend
 from qiskit import ClassicalRegister, QuantumRegister, QuantumCircuit
 from qiskit.utils import QuantumInstance
@@ -52,7 +51,7 @@ def __init__(
         self,
         evaluation_schedule: Union[List[int], int],
         minimizer: Optional[MINIMIZER] = None,
-        quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
         r"""
         Args:
@@ -109,15 +108,13 @@ def quantum_instance(self) -> Optional[QuantumInstance]:
         return self._quantum_instance
 
     @quantum_instance.setter
-    def quantum_instance(
-        self, quantum_instance: Union[QuantumInstance, BaseBackend, Backend]
-    ) -> None:
+    def quantum_instance(self, quantum_instance: Union[QuantumInstance, Backend]) -> None:
         """Set quantum instance.
 
         Args:
             quantum_instance: The quantum instance used to run this algorithm.
         """
-        if isinstance(quantum_instance, (BaseBackend, Backend)):
+        if isinstance(quantum_instance, Backend):
             quantum_instance = QuantumInstance(quantum_instance)
         self._quantum_instance = quantum_instance
 

qiskit_algorithms/aux_ops_evaluator.py

@@ -23,15 +23,15 @@
     OperatorBase,
     ExpectationBase,
 )
-from qiskit.providers import BaseBackend, Backend
+from qiskit.providers import Backend
 from qiskit.quantum_info import Statevector
 from qiskit.utils import QuantumInstance
 
 from .list_or_dict import ListOrDict
 
 
 def eval_observables(
-    quantum_instance: Union[QuantumInstance, BaseBackend, Backend],
+    quantum_instance: Union[QuantumInstance, Backend],
     quantum_state: Union[
         Statevector,
         QuantumCircuit,
@@ -161,7 +161,7 @@ def _compute_std_devs(
     observables_expect_sampled: OperatorBase,
     observables: ListOrDict[OperatorBase],
     expectation: ExpectationBase,
-    quantum_instance: Union[QuantumInstance, BaseBackend, Backend],
+    quantum_instance: Union[QuantumInstance, Backend],
 ) -> List[complex]:
     """
     Calculates a list of standard deviations from expectation values of observables provided.

qiskit_algorithms/factorizers/shor.py

@@ -25,7 +25,6 @@
 from qiskit.circuit import Gate, Instruction, ParameterVector
 from qiskit.circuit.library import QFT
 from qiskit.providers import Backend
-from qiskit.providers import BaseBackend
 from qiskit.quantum_info import partial_trace
 from qiskit.utils import summarize_circuits
 from qiskit.utils.arithmetic import is_power
@@ -51,9 +50,7 @@ class Shor:
     See also https://arxiv.org/abs/quant-ph/0205095
     """
 
-    def __init__(
-        self, quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]] = None
-    ) -> None:
+    def __init__(self, quantum_instance: Optional[Union[QuantumInstance, Backend]] = None) -> None:
         """
         Args:
             quantum_instance: Quantum Instance or Backend
@@ -69,11 +66,9 @@ def quantum_instance(self) -> Optional[QuantumInstance]:
         return self._quantum_instance
 
     @quantum_instance.setter
-    def quantum_instance(
-        self, quantum_instance: Union[QuantumInstance, BaseBackend, Backend]
-    ) -> None:
+    def quantum_instance(self, quantum_instance: Union[QuantumInstance, Backend]) -> None:
         """Sets quantum instance."""
-        if isinstance(quantum_instance, (BaseBackend, Backend)):
+        if isinstance(quantum_instance, Backend):
             quantum_instance = QuantumInstance(quantum_instance)
         self._quantum_instance = quantum_instance
 

qiskit_algorithms/linear_solvers/hhl.py

@@ -29,7 +29,7 @@
     ListOp,
     ExpectationFactory,
 )
-from qiskit.providers import Backend, BaseBackend
+from qiskit.providers import Backend
 from qiskit.quantum_info.operators.base_operator import BaseOperator
 from qiskit.utils import QuantumInstance
 
@@ -100,7 +100,7 @@ def __init__(
         self,
         epsilon: float = 1e-2,
         expectation: Optional[ExpectationBase] = None,
-        quantum_instance: Optional[Union[Backend, BaseBackend, QuantumInstance]] = None,
+        quantum_instance: Optional[Union[Backend, QuantumInstance]] = None,
     ) -> None:
         r"""
         Args:
@@ -142,9 +142,7 @@ def quantum_instance(self) -> Optional[QuantumInstance]:
         return None if self._sampler is None else self._sampler.quantum_instance
 
     @quantum_instance.setter
-    def quantum_instance(
-        self, quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]]
-    ) -> None:
+    def quantum_instance(self, quantum_instance: Optional[Union[QuantumInstance, Backend]]) -> None:
         """Set quantum instance.
 
         Args:

qiskit_algorithms/minimum_eigen_solvers/qaoa.py

@@ -20,7 +20,6 @@
 from qiskit.opflow import OperatorBase, ExpectationBase
 from qiskit.opflow.gradients import GradientBase
 from qiskit.providers import Backend
-from qiskit.providers import BaseBackend
 from qiskit.utils.quantum_instance import QuantumInstance
 from qiskit.utils.validation import validate_min
 from qiskit.circuit.library.n_local.qaoa_ansatz import QAOAAnsatz
@@ -65,7 +64,7 @@ def __init__(
         include_custom: bool = False,
         max_evals_grouped: int = 1,
         callback: Optional[Callable[[int, np.ndarray, float, float], None]] = None,
-        quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
         """
         Args:

qiskit_algorithms/minimum_eigen_solvers/vqe.py

@@ -24,7 +24,6 @@
 
 from qiskit.circuit import QuantumCircuit, Parameter
 from qiskit.circuit.library import RealAmplitudes
-from qiskit.providers import BaseBackend
 from qiskit.providers import Backend
 from qiskit.opflow import (
     OperatorBase,
@@ -145,7 +144,7 @@ def __init__(
         include_custom: bool = False,
         max_evals_grouped: int = 1,
         callback: Optional[Callable[[int, np.ndarray, float, float], None]] = None,
-        quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
         """
 
@@ -254,9 +253,7 @@ def quantum_instance(self) -> Optional[QuantumInstance]:
         return self._quantum_instance
 
     @quantum_instance.setter
-    def quantum_instance(
-        self, quantum_instance: Union[QuantumInstance, BaseBackend, Backend]
-    ) -> None:
+    def quantum_instance(self, quantum_instance: Union[QuantumInstance, Backend]) -> None:
         """Sets quantum_instance"""
         if not isinstance(quantum_instance, QuantumInstance):
             quantum_instance = QuantumInstance(quantum_instance)

qiskit_algorithms/phase_estimators/hamiltonian_phase_estimation.py

@@ -25,7 +25,7 @@
     PauliSumOp,
     StateFn,
 )
-from qiskit.providers import BaseBackend
+from qiskit.providers import Backend
 from .phase_estimation import PhaseEstimation
 from .hamiltonian_phase_estimation_result import HamiltonianPhaseEstimationResult
 from .phase_estimation_scale import PhaseEstimationScale
@@ -88,7 +88,7 @@ class HamiltonianPhaseEstimation:
     def __init__(
         self,
         num_evaluation_qubits: int,
-        quantum_instance: Optional[Union[QuantumInstance, BaseBackend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
         """
         Args:

qiskit_algorithms/phase_estimators/ipe.py

@@ -19,7 +19,7 @@
 import qiskit
 from qiskit.circuit import QuantumCircuit, QuantumRegister
 from qiskit.circuit.classicalregister import ClassicalRegister
-from qiskit.providers import BaseBackend, Backend
+from qiskit.providers import Backend
 from qiskit.utils import QuantumInstance
 from .phase_estimator import PhaseEstimator
 from .phase_estimator import PhaseEstimatorResult
@@ -38,7 +38,7 @@ class IterativePhaseEstimation(PhaseEstimator):
     def __init__(
         self,
         num_iterations: int,
-        quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
 
         """Args:
@@ -48,7 +48,7 @@ def __init__(
         Raises:
           ValueError: if num_iterations is not greater than zero.
         """
-        if isinstance(quantum_instance, (Backend, BaseBackend)):
+        if isinstance(quantum_instance, Backend):
             quantum_instance = QuantumInstance(quantum_instance)
         self._quantum_instance = quantum_instance
         if num_iterations <= 0:

qiskit_algorithms/phase_estimators/phase_estimation.py

@@ -21,7 +21,7 @@
 import qiskit
 from qiskit import circuit
 from qiskit.circuit.classicalregister import ClassicalRegister
-from qiskit.providers import BaseBackend, Backend
+from qiskit.providers import Backend
 from qiskit.utils import QuantumInstance
 from qiskit.result import Result
 from .phase_estimation_result import PhaseEstimationResult, _sort_phases
@@ -81,7 +81,7 @@ class PhaseEstimation(PhaseEstimator):
     def __init__(
         self,
         num_evaluation_qubits: int,
-        quantum_instance: Optional[Union[QuantumInstance, BaseBackend, Backend]] = None,
+        quantum_instance: Optional[Union[QuantumInstance, Backend]] = None,
     ) -> None:
         """
         Args:
@@ -94,7 +94,7 @@ def __init__(
         if num_evaluation_qubits is not None:
             self._num_evaluation_qubits = num_evaluation_qubits
 
-        if isinstance(quantum_instance, (Backend, BaseBackend)):
+        if isinstance(quantum_instance, Backend):
             quantum_instance = QuantumInstance(quantum_instance)
         self._quantum_instance = quantum_instance