Move qml.cond to ops.op_math (#4860)

* Moved `condition.py` from the `transforms` folder to `ops/op_math`.
`qml.transforms.Conditional` is now available as `qml.ops.Conditional`.
* Updated docs accordingly.

doc/releases/changelog-dev.md

@@ -51,6 +51,10 @@
 
 <h3>Breaking changes 💔</h3>
 
+* Moved `qml.cond` and the `Conditional` operation from the `transforms` folder to the `ops/op_math` folder.
+  `qml.transforms.Conditional` will now be available as `qml.ops.Conditional`.
+  [(#4860)](https://github.com/PennyLaneAI/pennylane/pull/4860)
+
 * The `prep` keyword argument has been removed from `QuantumScript` and `QuantumTape`.
   `StatePrepBase` operations should be placed at the beginning of the `ops` list instead.
   [(#4756)](https://github.com/PennyLaneAI/pennylane/pull/4756)

pennylane/__init__.py

@@ -69,7 +69,7 @@
     shadow_expval,
 )
 from pennylane.ops import *
-from pennylane.ops import adjoint, ctrl, exp, sum, pow, prod, s_prod
+from pennylane.ops import adjoint, ctrl, cond, exp, sum, pow, prod, s_prod
 from pennylane.templates import broadcast, layer
 from pennylane.templates.embeddings import *
 from pennylane.templates.layers import *
@@ -89,7 +89,6 @@
     cut_circuit,
     cut_circuit_mc,
     compile,
-    cond,
     defer_measurements,
     metric_tensor,
     specs,

pennylane/ops/op_math/__init__.py

@@ -24,6 +24,7 @@
 
     ~adjoint
     ~ctrl
+    ~cond
     ~exp
     ~sum
     ~pow
@@ -40,6 +41,7 @@
 
     ~Adjoint
     ~CompositeOp
+    ~Conditional
     ~Controlled
     ~ControlledOp
     ~Evolution
@@ -78,6 +80,7 @@
 
 from .adjoint import Adjoint, adjoint
 from .composite import CompositeOp
+from .condition import cond, Conditional
 from .controlled import Controlled, ControlledOp, ctrl
 from .controlled_ops import ControlledQubitUnitary, CY, CZ
 from .evolution import Evolution

pennylane/transforms/condition.py → pennylane/ops/op_math/condition.py

@@ -17,7 +17,6 @@
 from functools import wraps
 from typing import Type
 
-from pennylane.measurements import MeasurementValue
 from pennylane.operation import AnyWires, Operation
 from pennylane.tape import make_qscript
 
@@ -48,12 +47,7 @@ class Conditional(Operation):
 
     num_wires = AnyWires
 
-    def __init__(
-        self,
-        expr: MeasurementValue[bool],
-        then_op: Type[Operation],
-        id=None,
-    ):
+    def __init__(self, expr, then_op: Type[Operation], id=None):
         self.meas_val = expr
         self.then_op = then_op
         super().__init__(wires=then_op.wires, id=id)

pennylane/transforms/__init__.py

@@ -167,18 +167,6 @@
     ~draw
     ~draw_mpl
 
-
-Transforms that act on quantum functions
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-These transforms accept quantum functions (Python functions
-containing quantum operations) that are used to construct QNodes.
-
-.. autosummary::
-    :toctree: api
-
-    ~transforms.cond
-
 Decorators and utility functions
 --------------------------------
 
@@ -237,7 +225,6 @@
 from .batch_input import batch_input
 from .batch_partial import batch_partial
 from .classical_jacobian import classical_jacobian
-from .condition import cond, Conditional
 from .convert_to_numpy_parameters import convert_to_numpy_parameters
 from .compile import compile
 from .decompositions import (

tests/transforms/test_condition.py → tests/ops/op_math/test_condition.py

@@ -26,7 +26,7 @@
 import pytest
 
 import pennylane as qml
-from pennylane.transforms.condition import ConditionalTransformError
+from pennylane.ops.op_math.condition import ConditionalTransformError
 
 terminal_meas = [
     qml.probs(wires=[1, 0]),
@@ -64,16 +64,16 @@ def f(x):
         assert len(ops) == 4
         assert ops[0].return_type == qml.measurements.MidMeasure
 
-        assert isinstance(ops[1], qml.transforms.condition.Conditional)
+        assert isinstance(ops[1], qml.ops.Conditional)
         assert isinstance(ops[1].then_op, qml.PauliX)
         assert ops[1].then_op.wires == target_wire
 
-        assert isinstance(ops[2], qml.transforms.condition.Conditional)
+        assert isinstance(ops[2], qml.ops.Conditional)
         assert isinstance(ops[2].then_op, qml.RY)
         assert ops[2].then_op.wires == target_wire
         assert ops[2].then_op.data == (r,)
 
-        assert isinstance(ops[3], qml.transforms.condition.Conditional)
+        assert isinstance(ops[3], qml.ops.Conditional)
         assert isinstance(ops[3].then_op, qml.PauliZ)
         assert ops[3].then_op.wires == target_wire
 
@@ -129,20 +129,20 @@ def g(x):
 
         assert ops[0].return_type == qml.measurements.MidMeasure
 
-        assert isinstance(ops[1], qml.transforms.condition.Conditional)
+        assert isinstance(ops[1], qml.ops.Conditional)
         assert isinstance(ops[1].then_op, qml.PauliX)
         assert ops[1].then_op.wires == target_wire
 
-        assert isinstance(ops[2], qml.transforms.condition.Conditional)
+        assert isinstance(ops[2], qml.ops.Conditional)
         assert isinstance(ops[2].then_op, qml.RY)
         assert ops[2].then_op.wires == target_wire
         assert ops[2].then_op.data == (r,)
 
-        assert isinstance(ops[3], qml.transforms.condition.Conditional)
+        assert isinstance(ops[3], qml.ops.Conditional)
         assert isinstance(ops[3].then_op, qml.PauliZ)
         assert ops[3].then_op.wires == target_wire
 
-        assert isinstance(ops[4], qml.transforms.condition.Conditional)
+        assert isinstance(ops[4], qml.ops.Conditional)
         assert isinstance(ops[4].then_op, qml.PauliY)
         assert ops[4].then_op.wires == target_wire
 
@@ -224,12 +224,12 @@ def test_cond_operationss_with_adjoint(self, terminal_measurement):
         assert len(ops) == 3
         assert ops[0].return_type == qml.measurements.MidMeasure
 
-        assert isinstance(ops[1], qml.transforms.condition.Conditional)
+        assert isinstance(ops[1], qml.ops.Conditional)
         assert isinstance(ops[1].then_op, qml.ops.op_math.Adjoint)
         assert isinstance(ops[1].then_op.base, qml.RX)
         assert ops[1].then_op.wires == target_wire
 
-        assert isinstance(ops[2], qml.transforms.condition.Conditional)
+        assert isinstance(ops[2], qml.ops.Conditional)
         assert isinstance(ops[2].then_op, qml.RX)
         assert ops[2].then_op.data == (r,)
         assert ops[2].then_op.wires == target_wire
@@ -253,11 +253,11 @@ def test_cond_operationss_with_ctrl(self, terminal_measurement):
         assert len(ops) == 3
         assert ops[0].return_type == qml.measurements.MidMeasure
 
-        assert isinstance(ops[1], qml.transforms.condition.Conditional)
+        assert isinstance(ops[1], qml.ops.Conditional)
         assert isinstance(ops[1].then_op, qml.ops.op_math.Controlled)
         assert qml.equal(ops[1].then_op.base, qml.RX(r, wires=2))
 
-        assert isinstance(ops[2], qml.transforms.condition.Conditional)
+        assert isinstance(ops[2], qml.ops.Conditional)
         assert isinstance(ops[2].then_op, qml.ops.op_math.Controlled)
         assert qml.equal(ops[2].then_op.base, qml.RY(r, wires=2))
 
@@ -281,11 +281,11 @@ def test_ctrl_operations_with_cond(self, terminal_measurement):
         assert ops[0].return_type == qml.measurements.MidMeasure
 
         assert isinstance(ops[1], qml.ops.op_math.Controlled)
-        assert isinstance(ops[1].base, qml.transforms.condition.Conditional)
+        assert isinstance(ops[1].base, qml.ops.Conditional)
         assert qml.equal(ops[1].base.then_op, qml.RX(1.234, wires=0))
 
         assert isinstance(ops[2], qml.ops.op_math.Controlled)
-        assert isinstance(ops[2].base, qml.transforms.condition.Conditional)
+        assert isinstance(ops[2].base, qml.ops.Conditional)
         assert qml.equal(ops[2].base.then_op, qml.RY(r, wires=0))
 
         assert len(tape.measurements) == 1

tests/tape/test_tape.py

@@ -296,16 +296,16 @@ def f(x):
         assert len(tape.circuit) == 5
         assert tape.circuit[0].return_type == qml.measurements.MidMeasure
 
-        assert isinstance(tape.circuit[1], qml.transforms.condition.Conditional)
+        assert isinstance(tape.circuit[1], qml.ops.Conditional)
         assert isinstance(tape.circuit[1].then_op, qml.PauliX)
         assert tape.circuit[1].then_op.wires == target_wire
 
-        assert isinstance(tape.circuit[2], qml.transforms.condition.Conditional)
+        assert isinstance(tape.circuit[2], qml.ops.Conditional)
         assert isinstance(tape.circuit[2].then_op, qml.RY)
         assert tape.circuit[2].then_op.wires == target_wire
         assert tape.circuit[2].then_op.data == (r,)
 
-        assert isinstance(tape.circuit[3], qml.transforms.condition.Conditional)
+        assert isinstance(tape.circuit[3], qml.ops.Conditional)
         assert isinstance(tape.circuit[3].then_op, qml.PauliZ)
         assert tape.circuit[3].then_op.wires == target_wire