Lightning-AI/pytorch-lightning · error · ValueError

'{name}' is already present in the registry. HINT: Use `over

Error message

'{name}' is already present in the registry. HINT: Use `override=True`.

What it means

StrategyRegistry.register refuses to silently overwrite an existing registration unless override=True. Registering a name that already exists (built-in names like 'ddp', 'xla', etc., or a duplicate custom registration) raises this ValueError.

Source

Thrown at src/lightning/fabric/strategies/registry.py:66

        description: Optional[str] = None,
        override: bool = False,
        **init_params: Any,
    ) -> Callable:
        """Registers a strategy mapped to a name and with required metadata.

        Args:
            name : the name that identifies a strategy, e.g. "deepspeed_stage_3"
            strategy : strategy class
            description : strategy description
            override : overrides the registered strategy, if True
            init_params: parameters to initialize the strategy

        """
        if not (name is None or isinstance(name, str)):
            raise TypeError(f"`name` must be a str, found {name}")

        if name in self and not override:
            raise ValueError(f"'{name}' is already present in the registry. HINT: Use `override=True`.")

        data: dict[str, Any] = {}
        data["description"] = description if description is not None else ""

        data["init_params"] = init_params

        def do_register(strategy: Callable) -> Callable:
            data["strategy"] = strategy
            data["strategy_name"] = name
            self[name] = data
            return strategy

        if strategy is not None:
            return do_register(strategy)

        return do_register

    @override

View on GitHub (pinned to 9fed5c27d2)

Solutions

1. Choose a unique name not already in the registry (check registry.available_strategies())
2. If intentional replacement is desired, pass override=True: register('ddp', MyStrategy, override=True)
3. Guard registration: if 'my_strategy' not in registry: register(...)

Example fix

# before
register('ddp', MyStrategy)  # ValueError
# after
register('ddp', MyStrategy, override=True)
# or
if 'ddp' not in registry:
    register('ddp', MyStrategy)

if name in registry:
    print(f'{name} already registered; skipping or overriding')

try:
    registry.register(name, strategy)
except ValueError as e:
    if 'already present' in str(e):
        registry.register(name, strategy, override=True)
    else:
        raise

When it happens

Trigger: register('ddp', MyStrategy) when 'ddp' is already registered; registering the same custom strategy name twice, e.g. when a module is imported/reloaded or an extension runs twice.

Common situations: Plugins/extensions re-registering built-in strategy names; notebooks where cells re-execute registration code; library version upgrades adding a name a user had already registered.

Related errors

• `name` must be a str, found {name}
• '{}' not found in registry. Available names: {}
• Received multiple values for {', '.join(duplicated_plugin_ke
• Received both `precision={precision_input}` and `plugins={se
• accelerator set through both strategy class and accelerator

AI-assisted analysis of Lightning-AI/pytorch-lightning@9fed5c27d2 (2026-08-28). Data as JSON: /api/errors/32c47dd2efdb69a6. Report an issue: GitHub.