Remove usage of qiskit.extensions (#2023)

The module has been pending deprecation since Qiskit 0.45.
It is deprecated for 0.46 and removed in 1.0.

This removal concerns the import location of ``UnitaryGate`` and the
usage of the ``ExtensionError``. The first is easily fixed, whereas for
the latter I tried using ``ValueError`` or ``TypeError``, which seemed
to cover the error meanings. Technically, this is a breaking change and
we could introduce an intermediary class that inherits from the deprecated
``ExtensionError`` and the new choice of error. However, since we will
soon be changing to 1.0 and we also skipped this in Qiskit Terra (as we
thought it highly unlikely that users are actually relying on this error
type) it might be fine to just change the error type.

qiskit_aer/backends/aer_compiler.py

@@ -24,7 +24,7 @@
 from qiskit.circuit import QuantumCircuit, Clbit, ClassicalRegister, ParameterExpression
 from qiskit.circuit.classical.expr import Expr, Unary, Binary, Var, Value, ExprVisitor, iter_vars
 from qiskit.circuit.classical.types import Bool, Uint
-from qiskit.extensions import Initialize
+from qiskit.circuit.library import Initialize
 from qiskit.providers.options import Options
 from qiskit.pulse import Schedule, ScheduleBlock
 from qiskit.circuit.controlflow import (

qiskit_aer/backends/name_mapping.py

@@ -34,6 +34,8 @@
     CRZGate,
     MCU1Gate,
     MCXGrayCode,
+    Initialize,
+    UCGate,
 )
 from qiskit.circuit.controlflow import (
     IfElseOp,
@@ -43,8 +45,6 @@
     BreakLoopOp,
     SwitchCaseOp,
 )
-from qiskit.extensions import Initialize
-from qiskit.extensions.quantum_initializer import UCGate
 from qiskit.quantum_info.operators.channel.kraus import Kraus
 from qiskit.quantum_info.operators.channel import SuperOp
 from qiskit.quantum_info.operators.channel.quantum_channel import QuantumChannel

qiskit_aer/library/default_qubits.py

@@ -14,7 +14,6 @@
 """
 
 from qiskit.circuit import QuantumRegister
-from qiskit.extensions.exceptions import ExtensionError
 
 
 def default_qubits(circuit, qubits=None):
@@ -27,7 +26,7 @@ def default_qubits(circuit, qubits=None):
             [Default: None]
 
     Raises:
-            ExtensionError: if default qubits fails.
+        ValueError: if default qubits fails.
 
     Returns:
         list: qubits list.
@@ -37,9 +36,9 @@ def default_qubits(circuit, qubits=None):
     # This is needed for full register snapshots like statevector
     if isinstance(qubits, QuantumRegister):
         qubits = qubits[:]
-    if not qubits:
+    if qubits is None:
         qubits = list(circuit.qubits)
         if len(qubits) == 0:
-            raise ExtensionError("no qubits for snapshot")
+            raise ValueError("no qubits for snapshot")
 
     return qubits

qiskit_aer/library/save_instructions/save_amplitudes.py

@@ -14,7 +14,6 @@
 """
 
 from qiskit.circuit import QuantumCircuit
-from qiskit.extensions.exceptions import ExtensionError
 from .save_data import SaveSingleData, SaveAverageData
 from ..default_qubits import default_qubits
 
@@ -37,7 +36,7 @@ def __init__(self, num_qubits, params, label="amplitudes", pershot=False, condit
                                 [Default: False].
 
         Raises:
-            ExtensionError: if params is invalid for the specified number of qubits.
+            ValueError: if params is invalid for the specified number of qubits.
         """
         params = _format_amplitude_params(params, num_qubits)
         super().__init__(
@@ -78,7 +77,7 @@ def __init__(
                                 [Default: False].
 
         Raises:
-            ExtensionError: if params is invalid for the specified number of qubits.
+            ValueError: if params is invalid for the specified number of qubits.
         """
         params = _format_amplitude_params(params, num_qubits)
         super().__init__(
@@ -109,7 +108,7 @@ def save_amplitudes(self, params, label="amplitudes", pershot=False, conditional
         QuantumCircuit: with attached instruction.
 
     Raises:
-        ExtensionError: if params is invalid for the specified number of qubits.
+        ValueError: if params is invalid for the specified number of qubits.
     """
     qubits = default_qubits(self)
     instr = SaveAmplitudes(
@@ -139,7 +138,7 @@ def save_amplitudes_squared(
         QuantumCircuit: with attached instruction.
 
     Raises:
-        ExtensionError: if params is invalid for the specified number of qubits.
+        ValueError: if params is invalid for the specified number of qubits.
     """
     qubits = default_qubits(self)
     instr = SaveAmplitudesSquared(
@@ -161,7 +160,7 @@ def _format_amplitude_params(params, num_qubits=None):
         else:
             params = [int(i, 2) for i in params]
     if num_qubits and max(params) >= 2**num_qubits:
-        raise ExtensionError("Param values contain a state larger than the number of qubits")
+        raise ValueError("Param values contain a state larger than the number of qubits")
     return params
 
 

qiskit_aer/library/save_instructions/save_data.py

@@ -16,7 +16,6 @@
 import copy
 
 from qiskit.circuit import Instruction
-from qiskit.extensions.exceptions import ExtensionError
 
 
 class SaveData(Instruction):
@@ -39,19 +38,17 @@ def __init__(self, name, num_qubits, label, subtype="single", params=None):
                                    [Default: None].
 
         Raises:
-            ExtensionError: if the subtype string is invalid.
+            TypeError: if the subtype string is invalid.
 
         Additional Information:
             The supported subtypes are 'single', 'list', 'c_list', 'average',
             'c_average', 'accum', 'c_accum'.
         """
         if subtype not in self._allowed_subtypes:
-            raise ExtensionError("Invalid data subtype for SaveData instruction.")
+            raise TypeError("Invalid data subtype for SaveData instruction.")
 
         if not isinstance(label, str):
-            raise ExtensionError(
-                f"Invalid label for save data instruction, {label} must be a string."
-            )
+            raise TypeError(f"Invalid label for save data instruction, {label} must be a string.")
 
         if params is None:
             params = {}

qiskit_aer/library/save_instructions/save_expectation_value.py

@@ -16,7 +16,6 @@
 from numpy import allclose
 from qiskit.quantum_info import Pauli, SparsePauliOp, Operator
 from qiskit.circuit import QuantumCircuit
-from qiskit.extensions.exceptions import ExtensionError
 from .save_data import SaveAverageData
 
 
@@ -51,7 +50,8 @@ def __init__(
                                 values [Default: False].
 
         Raises:
-            ExtensionError: if the input operator is invalid or not Hermitian.
+            ValueError: if the input operator is not Hermitian.
+            TypeError: if the input operator is of invalid type.
 
         .. note::
 
@@ -64,7 +64,7 @@ def __init__(
         elif not isinstance(operator, SparsePauliOp):
             operator = SparsePauliOp.from_operator(Operator(operator))
         if not allclose(operator.coeffs.imag, 0):
-            raise ExtensionError("Input operator is not Hermitian.")
+            raise ValueError("Input operator is not Hermitian.")
         params = _expval_params(operator, variance=False)
         super().__init__(
             "save_expval",
@@ -109,7 +109,8 @@ def __init__(
                                 values [Default: False].
 
         Raises:
-            ExtensionError: if the input operator is invalid or not Hermitian.
+            ValueError: if the input operator is not Hermitian.
+            TypeError: if the input operator is of invalid type.
 
         .. note::
 
@@ -122,7 +123,7 @@ def __init__(
         elif not isinstance(operator, SparsePauliOp):
             operator = SparsePauliOp.from_operator(Operator(operator))
         if not allclose(operator.coeffs.imag, 0):
-            raise ExtensionError("Input operator is not Hermitian.")
+            raise ValueError("Input operator is not Hermitian.")
         params = _expval_params(operator, variance=True)
         super().__init__(
             "save_expval_var",
@@ -142,7 +143,7 @@ def _expval_params(operator, variance=False):
     elif not isinstance(operator, SparsePauliOp):
         operator = SparsePauliOp.from_operator(Operator(operator))
     if not isinstance(operator, SparsePauliOp):
-        raise ExtensionError("Invalid input operator")
+        raise TypeError("Invalid input operator")
 
     params = {}
 
@@ -196,7 +197,8 @@ def save_expectation_value(
         QuantumCircuit: with attached instruction.
 
     Raises:
-        ExtensionError: if the input operator is invalid or not Hermitian.
+        ValueError: if the input operator is not Hermitian.
+        TypeError: if the input operator is of invalid type.
 
     .. note::
 
@@ -237,7 +239,8 @@ def save_expectation_value_variance(
         QuantumCircuit: with attached instruction.
 
     Raises:
-        ExtensionError: if the input operator is invalid or not Hermitian.
+        ValueError: if the input operator is not Hermitian.
+        TypeError: if the input operator is of invalid type.
 
     .. note::
 

qiskit_aer/library/set_instructions/set_density_matrix.py

@@ -14,7 +14,6 @@
 """
 
 from qiskit.circuit import QuantumCircuit, Instruction
-from qiskit.extensions.exceptions import ExtensionError
 from qiskit.quantum_info import DensityMatrix
 from ..default_qubits import default_qubits
 
@@ -31,7 +30,7 @@ def __init__(self, state):
             state (DensityMatrix): a density matrix.
 
         Raises:
-            ExtensionError: if the input density matrix is not valid.
+            ValueError: if the input density matrix is not valid.
 
         .. note::
 
@@ -42,7 +41,7 @@ def __init__(self, state):
         if not isinstance(state, DensityMatrix):
             state = DensityMatrix(state)
         if not state.num_qubits or not state.is_valid():
-            raise ExtensionError("The input state is not valid")
+            raise ValueError("The input state is not valid")
         super().__init__("set_density_matrix", state.num_qubits, 0, [state.data])
 
 
@@ -56,8 +55,8 @@ def set_density_matrix(self, state):
         QuantumCircuit: with attached instruction.
 
     Raises:
-        ExtensionError: If the density matrix is the incorrect size for the
-                        current circuit.
+        ValueError: If the density matrix is the incorrect size for the
+            current circuit.
 
     .. note:
 
@@ -67,7 +66,7 @@ def set_density_matrix(self, state):
     if not isinstance(state, DensityMatrix):
         state = DensityMatrix(state)
     if not state.num_qubits or state.num_qubits != len(qubits):
-        raise ExtensionError(
+        raise ValueError(
             "The size of the density matrix for the set state"
             " instruction must be equal to the number of qubits"
             f" in the circuit (state.num_qubits ({state.num_qubits})"

qiskit_aer/library/set_instructions/set_matrix_product_state.py

@@ -14,7 +14,6 @@
 """
 
 from qiskit.circuit import QuantumCircuit, Instruction
-from qiskit.extensions.exceptions import ExtensionError
 from ..default_qubits import default_qubits
 
 
@@ -52,29 +51,29 @@ def set_matrix_product_state(self, state):
         QuantumCircuit: with attached instruction.
 
     Raises:
-        ExtensionError: If the structure of the state is incorrect
+        ValueError: If the structure of the state is incorrect
 
     .. note:
 
         This instruction is always defined across all qubits in a circuit.
     """
     qubits = default_qubits(self)
     if not isinstance(state, tuple) or len(state) != 2:
-        raise ExtensionError(
+        raise ValueError(
             "The input matrix product state is not valid.  Should be a list of 2 elements"
         )
     if not isinstance(state[0], list) or not isinstance(state[1], list):
-        raise ExtensionError(
+        raise ValueError(
             "The first element of the input matrix product state is not valid. Should be a list."
         )
     if len(state[0]) != len(state[1]) + 1:
-        raise ExtensionError(
+        raise ValueError(
             "The input matrix product state is not valid. "
             "Length of q_reg vector should be 1 more than length of lambda_reg"
         )
     for elem in state[0]:
         if not isinstance(elem, tuple) or len(elem) != 2:
-            raise ExtensionError(
+            raise ValueError(
                 "The input matrix product state is not valid."
                 "The first element should be a list of length 2"
             )

qiskit_aer/library/set_instructions/set_stabilizer.py

@@ -14,7 +14,6 @@
 """
 
 from qiskit.circuit import QuantumCircuit, Instruction
-from qiskit.extensions.exceptions import ExtensionError
 from qiskit.quantum_info import StabilizerState, Clifford
 from ..default_qubits import default_qubits
 
@@ -53,8 +52,8 @@ def set_stabilizer(self, state):
         QuantumCircuit: with attached instruction.
 
     Raises:
-        ExtensionError: If the state is the incorrect size for the
-                        current circuit.
+        ValueError: If the state is the incorrect size for the
+            current circuit.
 
     .. note:
 
@@ -66,7 +65,7 @@ def set_stabilizer(self, state):
     if not isinstance(state, Clifford):
         state = Clifford(state)
     if state.num_qubits != len(qubits):
-        raise ExtensionError(
+        raise ValueError(
             "The size of the Clifford for the set_stabilizer"
             " instruction must be equal to the number of qubits"
             f" in the circuit (state.num_qubits ({state.num_qubits})"

qiskit_aer/library/set_instructions/set_statevector.py

@@ -14,7 +14,6 @@
 """
 
 from qiskit.circuit import QuantumCircuit, Instruction
-from qiskit.extensions.exceptions import ExtensionError
 from qiskit.quantum_info import Statevector
 from ..default_qubits import default_qubits
 
@@ -31,7 +30,7 @@ def __init__(self, state):
             state (Statevector): a statevector.
 
         Raises:
-            ExtensionError: if the input is not a valid state.
+            ValueError: if the input is not a valid state.
 
         .. note::
 
@@ -42,7 +41,7 @@ def __init__(self, state):
         if not isinstance(state, Statevector):
             state = Statevector(state)
         if not state.num_qubits or not state.is_valid():
-            raise ExtensionError("The input statevector is not valid")
+            raise ValueError("The input statevector is not valid")
         super().__init__("set_statevector", state.num_qubits, 0, [state.data])
 
 
@@ -56,8 +55,8 @@ def set_statevector(self, state):
         QuantumCircuit: with attached instruction.
 
     Raises:
-        ExtensionError: If the state is the incorrect size for the
-                        current circuit.
+        ValueError: If the state is the incorrect size for the
+            current circuit.
 
     .. note:
 
@@ -67,7 +66,7 @@ def set_statevector(self, state):
     if not isinstance(state, Statevector):
         state = Statevector(state)
     if not state.num_qubits or state.num_qubits != len(qubits):
-        raise ExtensionError(
+        raise ValueError(
             "The size of the statevector for the set_statevector"
             " instruction must be equal to the number of qubits"
             f" in the circuit (state.num_qubits ({state.num_qubits})"