Remove deprecated SingleQubitGate (#5686)

Note: cirq.testing.SingleQubitGate still exists for brevity when writing tests.)

cirq-core/cirq/__init__.py

@@ -301,7 +301,6 @@
     rz,
     S,
     SingleQubitCliffordGate,
-    SingleQubitGate,
     SingleQubitPauliStringGateOperation,
     SQRT_ISWAP,
     SQRT_ISWAP_INV,

cirq-core/cirq/ops/__init__.py

@@ -87,7 +87,7 @@
 
 from cirq.ops.fsim_gate import FSimGate, PhasedFSimGate
 
-from cirq.ops.gate_features import InterchangeableQubitsGate, SingleQubitGate
+from cirq.ops.gate_features import InterchangeableQubitsGate
 
 from cirq.ops.gate_operation import GateOperation
 

cirq-core/cirq/ops/gate_features.py

@@ -18,11 +18,6 @@
 """
 
 import abc
-import warnings
-
-from cirq import value
-from cirq._compat import deprecated_class
-from cirq.ops import raw_types
 
 
 class InterchangeableQubitsGate(metaclass=abc.ABCMeta):
@@ -31,21 +26,3 @@ class InterchangeableQubitsGate(metaclass=abc.ABCMeta):
     def qubit_index_to_equivalence_group_key(self, index: int) -> int:
         """Returns a key that differs between non-interchangeable qubits."""
         return 0
-
-
-class _SingleQubitGateMeta(value.ABCMetaImplementAnyOneOf):
-    def __instancecheck__(cls, instance):
-        warnings.warn(
-            'isinstance(gate, SingleQubitGate) is deprecated. '
-            'Use cirq.num_qubits(gate) == 1 instead',
-            DeprecationWarning,
-        )
-        return isinstance(instance, raw_types.Gate) and instance._num_qubits_() == 1
-
-
-@deprecated_class(deadline='v1.0', fix='Define _num_qubits_ manually.')
-class SingleQubitGate(raw_types.Gate, metaclass=_SingleQubitGateMeta):
-    """A gate that must be applied to exactly one qubit."""
-
-    def _num_qubits_(self) -> int:
-        return 1

cirq-core/cirq/ops/gate_features_test.py

@@ -15,71 +15,6 @@
 import pytest
 
 import cirq
-from cirq.testing import assert_deprecated
-
-
-def test_single_qubit_gate_validate_args():
-    class Dummy(cirq.SingleQubitGate):
-        def matrix(self):
-            pass
-
-    with assert_deprecated(deadline="v1.0"):
-        g = Dummy()
-
-    with assert_deprecated(deadline="isinstance(gate, SingleQubitGate) is deprecated"):
-        assert isinstance(g, cirq.SingleQubitGate)
-    q1 = cirq.NamedQubit('q1')
-    q2 = cirq.NamedQubit('q2')
-
-    assert g.num_qubits() == 1
-    g.validate_args([q1])
-    g.validate_args([q2])
-    with pytest.raises(ValueError):
-        g.validate_args([])
-    with pytest.raises(ValueError):
-        g.validate_args([q1, q2])
-
-
-def test_single_qubit_gate_validates_on_each():
-    class Dummy(cirq.Gate):
-        def matrix(self):
-            pass
-
-        def _num_qubits_(self) -> int:
-            return 1
-
-    g = Dummy()
-    assert g.num_qubits() == 1
-
-    test_qubits = [cirq.NamedQubit(str(i)) for i in range(3)]
-
-    _ = g.on_each(*test_qubits)
-    _ = g.on_each(test_qubits)
-
-    test_non_qubits = [str(i) for i in range(3)]
-    with pytest.raises(ValueError):
-        _ = g.on_each(*test_non_qubits)
-    with pytest.raises(ValueError):
-        _ = g.on_each(*test_non_qubits)
-
-
-def test_single_qubit_validates_on():
-    class Dummy(cirq.Gate):
-        def matrix(self):
-            pass
-
-        def _num_qubits_(self) -> int:
-            return 1
-
-    g = Dummy()
-    assert g.num_qubits() == 1
-
-    test_qubits = [cirq.NamedQubit(str(i)) for i in range(3)]
-
-    with pytest.raises(ValueError):
-        _ = g.on(*test_qubits)
-    with pytest.raises(ValueError):
-        _ = g.on(*test_qubits)
 
 
 def test_qasm_output_args_validate():

cirq-core/cirq/ops/gate_operation_test.py

@@ -499,8 +499,6 @@ def all_subclasses(cls):
         cirq.circuits.quil_output.QuilTwoQubitGate,
         cirq.circuits.quil_output.QuilOneQubitGate,
         cirq.ops.MSGate,
-        # Gate features.
-        cirq.SingleQubitGate,
         # Interop gates
         cirq.interop.quirk.QuirkQubitPermutationGate,
         cirq.interop.quirk.QuirkArithmeticGate,

cirq-core/cirq/ops/raw_types.py

@@ -192,8 +192,7 @@ class Gate(metaclass=value.ABCMetaImplementAnyOneOf):
 
     Gates operate on a certain number of qubits. All implementations of gate
     must implement the `num_qubits` method declaring how many qubits they
-    act on. The gate feature classes `SingleQubitGate` and `TwoQubitGate`
-    can be used to avoid writing this boilerplate.
+    act on.
 
     Linear combinations of gates can be created by adding gates together and
     multiplying them by scalars.

cirq-core/cirq/protocols/json_test_data/spec.py

@@ -117,7 +117,6 @@
         'Device',
         'InterchangeableQubitsGate',
         'Pauli',
-        'SingleQubitGate',
         'ABCMetaImplementAnyOneOf',
         'SimulatesAmplitudes',
         'SimulatesExpectationValues',

cirq-core/cirq/transformers/analytical_decompositions/single_qubit_decompositions.py

@@ -15,7 +15,7 @@
 """Utility methods related to optimizing quantum circuits."""
 
 import math
-from typing import List, Optional, Tuple, cast
+from typing import List, Optional, Tuple
 
 import numpy as np
 import sympy
@@ -111,7 +111,7 @@ def single_qubit_matrix_to_gates(mat: np.ndarray, tolerance: float = 0) -> List[
             operation.
     """
     rotations = single_qubit_matrix_to_pauli_rotations(mat, tolerance)
-    return [cast(ops.SingleQubitGate, pauli) ** ht for pauli, ht in rotations]
+    return [pauli**ht for pauli, ht in rotations]
 
 
 def single_qubit_op_to_framed_phase_form(mat: np.ndarray) -> Tuple[np.ndarray, complex, complex]:

docs/build/custom_gates.ipynb

@@ -222,15 +222,6 @@
     "print(res)"
    ]
   },
-  {
-   "cell_type": "markdown",
-   "metadata": {
-    "id": "874bdef876ed"
-   },
-   "source": [
-    "An alternative to inheriting from `cirq.Gate` is to inherit from `cirq.SingleQubitGate`, in which case defining `_num_qubits_` is unnecessary. An example of a defining a two-qubit gate is shown below."
-   ]
-  },
   {
    "cell_type": "code",
    "execution_count": null,

docs/simulate/noisy_simulation.ipynb

@@ -476,7 +476,9 @@
    "outputs": [],
    "source": [
     "\"\"\"Minimal example of defining a custom channel.\"\"\"\n",
-    "class BitAndPhaseFlipChannel(cirq.SingleQubitGate):\n",
+    "class BitAndPhaseFlipChannel(cirq.Gate):\n",
+    "    def _num_qubits_(self) -> int:\n",
+    "        return 1\n",
     "    def __init__(self, p: float) -> None:\n",
     "        self._p = p\n",
     "    \n",

docs/start/intro.ipynb

@@ -1525,7 +1525,7 @@
     "\\end{array} \\right]\n",
     "$$\n",
     "\n",
-    "Below is a simple implementation of this gate in Cirq.  To do this we simply define a class that inherits from `cirq.SingleQubitGate` and implements the `cirq.SupportsUnitary` protocol by implementing the `_unitary_(self)` method.  We also define an optional `__str__` representation which Cirq will use when printing this gate out in a circuit diagram."
+    "Below is a simple implementation of this gate in Cirq.  To do this we simply define a class that inherits from `cirq.Gate` and implements the `cirq.SupportsUnitary` protocol by implementing the `_unitary_(self)` method.  We also define an optional `__str__` representation which Cirq will use when printing this gate out in a circuit diagram."
    ]
   },
   {
@@ -1539,7 +1539,9 @@
     "\"\"\"Example of defining a custom gate in Cirq.\"\"\"\n",
     "\n",
     "\n",
-    "class RationalGate(cirq.SingleQubitGate):\n",
+    "class RationalGate(cirq.Gate):\n",
+    "    def _num_qubits_(self) -> int:\n",
+    "        return 1\n",
     "    def _unitary_(self):\n",
     "        return np.array([[3 / 5, 4 / 5], [-4 / 5, 3 / 5]])\n",
     "\n",
@@ -1780,7 +1782,9 @@
     "\"\"\"Example of a custom gate which supports the decompose protocol.\"\"\"\n",
     "\n",
     "\n",
-    "class HXGate(cirq.SingleQubitGate):\n",
+    "class HXGate(cirq.Gate):\n",
+    "    def _num_qubits_(self) -> int:\n",
+    "        return 1\n",
     "    def _decompose_(self, qubits):\n",
     "        return cirq.H(*qubits), cirq.X(*qubits)\n",
     "\n",
@@ -2832,7 +2836,9 @@
    },
    "outputs": [],
    "source": [
-    "class InconsistentXGate(cirq.SingleQubitGate):\n",
+    "class InconsistentXGate(cirq.Gate):\n",
+    "    def _num_qubits_(self) -> int:\n",
+    "        return 1\n",
     "    def _decompose_(self, qubits):\n",
     "        yield cirq.H(qubits[0])\n",
     "        yield cirq.Z(qubits[0])\n",