nautechsystems/nautilus_trader · error

LiveNode.add_exec_algorithm requires a Python v2 ExecutionAl

Error message

LiveNode.add_exec_algorithm requires a Python v2 ExecutionAlgorithm instance; use add_exec_algorithm_from_config for DataActor-based algorithms: {e}

What it means

Raised by LiveNode.add_exec_algorithm when the supplied object cannot be extracted as a native PyExecutionAlgorithm (v2 Python execution algorithm). The message itself points to the remedy: DataActor-based (pure-Python actor) algorithms must be added via add_exec_algorithm_from_config instead.

Source

Thrown at crates/live/src/python/node.rs:1466

            return Err(to_pyruntime_err(
                "Cannot add exec algorithm while node is running, add exec algorithms before running the node",
            ));
        }

        log::debug!("`add_exec_algorithm` with a constructed instance");

        let exec_algorithm = exec_algorithm.clone().unbind();
        let py_exec_algorithm = Python::attach(|py| -> anyhow::Result<PyExecutionAlgorithm> {
            let bound = exec_algorithm.bind(py);
            let config = bound
                .getattr("config")
                .ok()
                .filter(|config| !config.is_none());
            let mut py_exec_algorithm_ref = bound
                .extract::<PyRefMut<PyExecutionAlgorithm>>()
                .map_err(Into::<PyErr>::into)
                .map_err(|e| {
                    anyhow::anyhow!(
                        "LiveNode.add_exec_algorithm requires a Python v2 ExecutionAlgorithm instance; use add_exec_algorithm_from_config for DataActor-based algorithms: {e}"
                    )
                })?;

            if let Some(config) = config.as_ref() {
                py_exec_algorithm_ref.configure_from_py_config(config)?;
            }

            py_exec_algorithm_ref.set_python_instance(bound)?;
            Ok(py_exec_algorithm_ref.clone())
        })
        .map_err(to_pyruntime_err)?;

        let exec_algorithm_id = self
            .node_mut()?
            .kernel_mut()
            .trader
            .borrow_mut()

View on GitHub (pinned to 18893faf8b)

Solutions

1. If the algorithm is DataActor-based, switch the call to add_exec_algorithm_from_config with its config
2. If it should be a v2 instance, ensure the class subclasses nautilus_trader's ExecutionAlgorithm
3. Check import paths — nautilus_trader.execution.algorithm vs custom modules
4. Use the config path end-to-end for consistency

Example fix

// before
node.add_exec_algorithm(MyDataActorBasedAlgo(config))
// after
node.add_exec_algorithm_from_config(MyExecAlgoConfig(...))

from nautilus_trader.execution.algorithm import ExecutionAlgorithm
assert isinstance(algo, ExecutionAlgorithm), "use add_exec_algorithm_from_config for DataActor-based algos"

def is_v2_exec_algorithm(obj) -> bool:
    from nautilus_trader.execution.algorithm import ExecutionAlgorithm
    return isinstance(obj, ExecutionAlgorithm)

try:
    node.add_exec_algorithm(algo)
except Exception as e:
    if "requires a Python v2 ExecutionAlgorithm" in str(e):
        node.add_exec_algorithm_from_config(algo.config)
    else:
        raise

When it happens

Trigger: Calling add_exec_algorithm with an object that is not a v2 pyo3-backed ExecutionAlgorithm instance — e.g. a DataActor/exec-actor subclass built from config, or a custom class not deriving from nautilus_trader.ExecutionAlgorithm.

Common situations: Mixing the two registration APIs after refactor; passing an algorithm built with a config object to the instance-based API; porting strategies from the pure-Python engine.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Failed to extract PyDataActor: {e}
• Python on_order failed: {e}
• Data client '{name}' is already registered
• Execution client '{name}' is already registered
• Cannot modify order in place: status is {status:?}, expected

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/5bf9e909595ea491. Report an issue: GitHub.