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Fix pickle handling for SingletonGate class #10871

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merged 5 commits into from
Sep 28, 2023
Merged

Fix pickle handling for SingletonGate class #10871

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5c9f223
Fix pickle handling for SingletonGate class
mtreinish Sep 20, 2023
05b8cae
Merge branch 'main' into fix-pickle-singletons
mtreinish Sep 20, 2023
3ad38b4
Use __getnewargs_ex__ insetad of __reduce__ & __setstate__
mtreinish Sep 22, 2023
c24edc1
Improve assertion in immutable pickle test
mtreinish Sep 22, 2023
79ab4fe
Merge branch 'main' into fix-pickle-singletons
mtreinish Sep 22, 2023
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5 changes: 5 additions & 0 deletions qiskit/circuit/singleton_gate.py
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Original file line number Diff line number Diff line change
Expand Up @@ -80,6 +80,11 @@ def __init__(self, *args, _condition=None, **kwargs):
super().__init__(*args, **kwargs)
self._condition = _condition

def __getnewargs_ex__(self):
if not self.mutable:
return ((), {})
return ((self.label, self._condition, self.duration, self.unit), {})

def c_if(self, classical, val):
if not isinstance(classical, (ClassicalRegister, Clbit)):
raise CircuitError("c_if must be used with a classical register or classical bit")
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26 changes: 26 additions & 0 deletions test/python/circuit/test_singleton_gate.py
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Expand Up @@ -18,6 +18,8 @@
"""

import copy
import io
import pickle

from qiskit.circuit.library import HGate, SXGate
from qiskit.circuit import Clbit, QuantumCircuit, QuantumRegister, ClassicalRegister
Expand Down Expand Up @@ -251,3 +253,27 @@ def test_positional_label(self):
label_gate = SXGate("I am a little label")
self.assertIsNot(gate, label_gate)
self.assertEqual(label_gate.label, "I am a little label")

def test_immutable_pickle(self):
gate = SXGate()
self.assertFalse(gate.mutable)
with io.BytesIO() as fd:
pickle.dump(gate, fd)
fd.seek(0)
copied = pickle.load(fd)
Comment on lines +260 to +263
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Totally unimportant, but pickle allows serialisation to bytes directly, so you can do this as a one-liner if you prefer: copied = pickle.loads(pickle.dumps(gate)).

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I just don't like using pickle.dumps because s implies string to me and it's not a string :D

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Rest in peace, Python 2 🙂

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maybe it's an initial from a language that reads right-to-left: "DUMP byteS" instead of "DUMP String" lol

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Here's the Python 2 docstring for dumps 🙂 : "Return the pickled representation of the object as a string, instead of writing it to a file."

self.assertFalse(copied.mutable)
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self.assertIs(copied, gate)

def test_mutable_pickle(self):
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One thing that surprised me with this issue is that it was not caught in this repo before the singleton gate PR was merged. I expect there is a good set of tests for transpiling conditional gates, but likely the tests all transpile a single circuit and don't hit the pickling issues that come up with parallel transpilation. I wonder if the tests added here are enough or if there should be more tests of pickling and unpickling circuits.

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There's actually not a vast amount of testing of conditional gates (with .condition set), because they typically weren't executable on anything but simulators until IBM hardware grew support for midcircuit measurements and more generalised control flow, at which point we began pivoting to IfElseOp.

The bug getting through points to a deficiency in integration testing around conditional gates for sure, and we can add more tests along those lines until Instruction.condition is completely removed in 1.0. Conditionals after transpilation are also harder to write good tests about, because we can't just test for unitary equivalence or anything like that when they're present, so it's easier for stuff to slip through.

gate = SXGate()
clbit = Clbit()
condition_gate = gate.c_if(clbit, 0)
self.assertIsNot(gate, condition_gate)
self.assertEqual(condition_gate.condition, (clbit, 0))
self.assertTrue(condition_gate.mutable)
with io.BytesIO() as fd:
pickle.dump(condition_gate, fd)
fd.seek(0)
copied = pickle.load(fd)
self.assertEqual(copied, condition_gate)
self.assertTrue(copied.mutable)
14 changes: 14 additions & 0 deletions test/python/compiler/test_transpiler.py
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Expand Up @@ -2173,6 +2173,20 @@ def run(self, dag):
added_cal = qc_test.calibrations["sx"][((0,), ())]
self.assertEqual(added_cal, ref_cal)

@data(0, 1, 2, 3)
def test_parallel_singleton_conditional_gate(self, opt_level):
"""Test that singleton mutable instance doesn't lose state in parallel."""
backend = FakeNairobiV2()
circ = QuantumCircuit(2, 1)
circ.h(0)
circ.measure(0, circ.clbits[0])
circ.z(1).c_if(circ.clbits[0], 1)
res = transpile(
[circ, circ], backend, optimization_level=opt_level, seed_transpiler=123456769
)
self.assertTrue(res[0].data[-1].operation.mutable)
self.assertEqual(res[0].data[-1].operation.condition, (res[0].clbits[0], 1))

@data(0, 1, 2, 3)
def test_backendv2_and_basis_gates(self, opt_level):
"""Test transpile() with BackendV2 and basis_gates set."""
Expand Down