Exceptions

Every MENOS failure is one of five exception types. They are created by the native extension, so a C++ exception surfaces as exactly one of them with no translation step.

text

MenosError                      base class; catch this to handle any MENOS failure
├── InvalidCircuitError         the request or circuit is malformed
├── UnsupportedFeatureError     valid, but MENOS cannot represent or execute it
├── ResourceExceededError       no plan fits the memory or time budget
└── InternalError               a MENOS invariant was violated

python

from menos.exceptions import (
    InternalError,
    InvalidCircuitError,
    MenosError,
    ResourceExceededError,
    UnsupportedFeatureError,
)

They are also exported from menos. The classes' own module is menos._core; menos.exceptions is the stable import path.

`InvalidCircuitError`

The circuit or output request is wrong.

Example message
`request asks for neither counts (shots=0) nor a statevector nor an expectation; nothing to produce`
`shots > 0 was requested but the circuit has no Measure operation`
`operation 0 (rx): unbound parameter(s) [Parameter(t)]; bind all parameters before running (QuantumCircuit.assign_parameters)`
`operation 0: qubit index 5 … out of range`
`Unitary matrix is not unitary within tolerance`

`UnsupportedFeatureError`

A valid circuit using something MENOS does not support.

Example message
`operation 1: qubit 0 has a non-terminal measurement (an operation follows a measurement of this qubit)`
`operation 1 (reset): not a MENOS-supported named gate and has no matrix representation; unsupported. Try transpile(qc, backend) first.`
`operation 0 (qft): acts on 6 qubits, exceeding kMaxUnitaryQubits=5, and is not a MENOS-supported named gate. Try transpile(qc, backend) first.`
`MENOSEstimator does not currently support parameterized circuits (1 unbound parameter(s)); bind all parameters first (QuantumCircuit.assign_parameters).`

`ResourceExceededError`

No plan fits. See ResourceExceeded.

Example message
`plan_job: no feasible candidate -- direct dense simulation requires 17592186044416 bytes, budget is 7752519680 bytes; …`
`plan_job: no feasible candidate within the time budget of … s -- estimated runtime … s exceeds the job's time budget of … s; …`
`menos::run: observed runtime of … s exceeded the job's time budget of … s after … safe boundaries on engine=… backend=…, and no different plan meets that budget -- …`

`InternalError`

MENOS detected that one of its own invariants was violated. Seeing one means a bug, a corrupted plan, or a degenerate case MENOS does not yet handle, not a mistake in your code. One known case: an observable whose every term is the identity (details). CUDA failures that occur despite the budget check also surface as InternalError, for example a device error message such as cuda: cudaMemcpyToSymbol (matrix) failed: ….

Other exceptions you may see

The Qiskit layer raises ordinary Python exceptions for misuse of the interface:

Exception	When
`TypeError`	`MENOSBackend.run` was given something other than a `QuantumCircuit`
`ValueError`	`MENOSBackend.run` was given more than one circuit
`AttributeError`	An unknown option or backend field

Verification

python

from menos import InvalidCircuitError, ResourceExceededError
from menos.exceptions import (
    InternalError,
    MenosError,
    UnsupportedFeatureError,
)

for error in (InvalidCircuitError, UnsupportedFeatureError, ResourceExceededError, InternalError):
    assert issubclass(error, MenosError)
assert issubclass(MenosError, Exception)
assert MenosError.__mro__[1] is Exception

Exceptions ​

InvalidCircuitError ​

UnsupportedFeatureError ​

ResourceExceededError ​

InternalError ​

Other exceptions you may see ​

Verification ​