What causes "Execution factory extractor '{name}' is already registered" in nautechsystems/nautilus_trader?

Make registration idempotent — register once per process.

Execution factory extractor '{name}' is already registered

Error message

Execution factory extractor '{name}' is already registered

What it means

Duplicate-registration guard in the Python system registry's register_exec_factory_extractor: an execution factory extractor with the same name is already registered, so the second registration would silently overwrite it and is rejected.

Source

Thrown at crates/system/src/python/registry.rs:119

        extractors.insert(type_name, extractor);
        Ok(())
    }

    /// Registers an execution factory extractor for a specific factory name.
    ///
    /// # Errors
    ///
    /// Returns an error if a factory with the same name is already registered.
    pub fn register_exec_factory_extractor(
        &self,
        name: String,
        extractor: ExecutionFactoryExtractor,
    ) -> anyhow::Result<()> {
        let mut extractors = self.exec_factory_extractors.lock();

        if extractors.contains_key(&name) {
            anyhow::bail!("Execution factory extractor '{name}' is already registered");
        }
        extractors.insert(name, extractor);
        Ok(())
    }

    /// Registers a simulated execution factory extractor for a specific factory name.
    ///
    /// # Errors
    ///
    /// Returns an error if a factory with the same name is already registered.
    pub fn register_sim_exec_factory_extractor(
        &self,
        name: String,
        extractor: SimulatedExecutionFactoryExtractor,
    ) -> anyhow::Result<()> {
        let mut extractors = self.sim_exec_factory_extractors.lock();

        if extractors.contains_key(&name) {

View on GitHub (pinned to 18893faf8b)

Solutions

Make registration idempotent — register once per process.
Use a distinct name for custom exec factories.
If re-running in a notebook, recreate the registry/kernel instead of re-registering.

Example fix

// before
register_exec_factory_extractor("MyExecClient", factory)  # second call fails
// after
if "MyExecClient" not in registered_names:
    register_exec_factory_extractor("MyExecClient", factory)

Defensive patterns

Strategy: try-catch

Validate before calling

if name in registered_exec_factories:
    return
registered_exec_factories.add(name)
register_exec_factory_extractor(name, factory)

Type guard

def exec_factory_registered(name: str, names: set) -> bool:
    return name in names

Try / catch

try:
    register_exec_factory_extractor(name, factory)
except Exception as e:
    if "is already registered" in str(e):
        pass  # idempotent re-setup
    else:
        raise

Prevention

Wrap exec factory registration in an idempotent setup function
Use unique adapter names per venue/factory
Don't re-run node setup cells/notebook code in the same process

When it happens

Trigger: Calling the public register_exec_factory_extractor twice with the same `name`, e.g. double plugin registration, module reload, or two exec client adapters sharing a name.

Common situations: Re-running system kernel/node setup in the same process (tests, notebooks), importing a third-party exec factory twice, name collisions between venue adapters.

Understand the failure class

Background: "already exists" / EEXIST / FileAlreadyExistsException: what the 'file already exists' error means and how to fix it — this error's family across 37 libraries.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/123031e72844cb0c. Report an issue: GitHub.