What causes "Failed to get config class {config_class_name}: {e}" in nautechsystems/nautilus_trader?

Confirm the config class name matches its definition in the module

Failed to get config class {config_class_name}: {e}

Error message

Failed to get config class {config_class_name}: {e}

What it means

Raised by `create_config_instance` when the config module imported successfully but `getattr` cannot find the named config class on it. The referenced config class does not exist under that name in that module.

Source

Thrown at crates/system/src/python/registration.rs:582

    };

    if config_module_name.is_empty()
        || config_class_name.is_empty()
        || config_class_name.contains(':')
    {
        anyhow::bail!("config_path must be in format 'module.path:ClassName', was {config_path}");
    }

    log::debug!(
        "Importing config class from module: {config_module_name} class: {config_class_name}"
    );

    let config_module = py
        .import(config_module_name)
        .map_err(|e| anyhow::anyhow!("Failed to import config module {config_module_name}: {e}"))?;
    let config_class = config_module
        .getattr(config_class_name)
        .map_err(|e| anyhow::anyhow!("Failed to get config class {config_class_name}: {e}"))?;
    let py_dict = PyDict::new(py);

    for (key, value) in config {
        let py_value = config_value_to_py(py, key, value)?;
        py_dict.set_item(key, py_value)?;
    }

    let config_instance = match config_class.call((), Some(&py_dict)) {
        Ok(instance) => instance,
        Err(kwargs_err) => match config_class.call0() {
            Ok(instance) => {
                for (key, value) in config {
                    let py_value = config_value_to_py(py, key, value)?;

                    if let Err(setattr_err) = instance.setattr(key, py_value) {
                        anyhow::bail!("Failed to set attribute {key}: {setattr_err}");
                    }
                }

View on GitHub (pinned to 18893faf8b)

Solutions

Confirm the config class name matches its definition in the module
Re-export the class at the module's top level or update the config path
Grep the module for `class <Name>` to find the correct current name

Example fix

// before
config_path = "my_package.config:MyActorConf"
// after
config_path = "my_package.config:MyActorConfig"

Defensive patterns

Strategy: validation

Validate before calling

from importlib import import_module
mod_path, cls = config_path.split(":")
assert hasattr(import_module(mod_path), cls), f"no config class {cls} in {mod_path}"

Try / catch

try:
    trader.add_actor(actor_config)
except Exception as e:
    if "Failed to get config class" in str(e):
        logging.error("verify config class name: %s", e)
    raise

Prevention

Match config class names exactly as defined in source
Re-export config classes from stable module paths
Avoid referring to nested classes in config paths

When it happens

Trigger: A `config_path` of the form `module:ConfigClass` where the config class is misspelled, was renamed, or lives in a different module than specified while instantiating a Python actor/strategy config.

Common situations: Renaming `*Config` dataclasses during refactors with stale configs pointing at old names; referring to an inner/non-top-level class; case mismatch.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/79b72dd15486e9f5. Report an issue: GitHub.