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[python] Surface dem_from_kernel errors as RuntimeError #4676

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[python] Surface dem_from_kernel errors as RuntimeError #4676

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[python] Surface dem_from_kernel errors as RuntimeError instead of ab…
mitchdz Jun 5, 2026
906443e
[python] Preserve Python exceptions in dem_from_kernel error guard
mitchdz Jun 5, 2026
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22 changes: 18 additions & 4 deletions python/runtime/cudaq/analysis/py_dem.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@
#include <nanobind/stl/optional.h>
#include <nanobind/stl/string.h>
#include <optional>
#include <stdexcept>
#include <string>

using namespace cudaq;
Expand All @@ -27,10 +28,23 @@ static std::string dem_from_kernel_impl(const std::string &kernelName,
args = simplifiedValidateInputArguments(args);

const cudaq::noise_model *noisePtr = noise ? &(*noise) : nullptr;
return cudaq::detail::runDemFromKernel(kernelName, platform, noisePtr, [&]() {
[[maybe_unused]] auto result =
cudaq::marshal_and_launch_module(kernelName, kernelMod, args);
});
// Re-throw as a module-local RuntimeError; plugin exceptions otherwise
// escape uncaught on macOS and abort instead of raising in Python.
try {
return cudaq::detail::runDemFromKernel(
kernelName, platform, noisePtr, [&]() {
[[maybe_unused]] auto result =
cudaq::marshal_and_launch_module(kernelName, kernelMod, args);
});
} catch (nanobind::python_error &) {
throw; // keep real Python exceptions (e.g. from argument marshalling)
} catch (const std::exception &e) {
throw std::runtime_error(e.what()); // dem_from_kernel reports via RuntimeError
} catch (...) {
throw std::runtime_error(
"cudaq::dem_from_kernel failed: the kernel uses an operation the Stim "
"analysis backend cannot simulate (only Clifford gates are supported).");
}
}

void cudaq::bindDemFromKernel(nanobind::module_ &mod) {
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