Lightning-AI/pytorch-lightning · error · MisconfigurationException

precision set through both strategy class and plugins, choos

Error message

precision set through both strategy class and plugins, choose one

What it means

A Strategy instance passed via Trainer(strategy=...) may already have a precision plugin attached (strategy._precision_plugin). Setting Trainer(plugins=[<Precision>...]) at the same time is rejected to avoid two competing precision configurations.

Source

Thrown at src/lightning/pytorch/trainer/connectors/accelerator_connector.py:280

                    f" Choose one."
                )

        self._precision_flag = "32-true" if precision_flag is None else precision_flag

        # handle the case when the user passes in a strategy instance which has an accelerator, precision,
        # checkpoint io or cluster env set up
        # TODO: improve the error messages below
        if self._strategy_flag and isinstance(self._strategy_flag, Strategy):
            if self._strategy_flag._accelerator:
                if self._accelerator_flag != "auto":
                    raise MisconfigurationException(
                        "accelerator set through both strategy class and accelerator flag, choose one"
                    )
                self._accelerator_flag = self._strategy_flag._accelerator
            if self._strategy_flag._precision_plugin:
                # [RFC] handle precision plugin set up conflict?
                if self._precision_plugin_flag:
                    raise MisconfigurationException("precision set through both strategy class and plugins, choose one")
                self._precision_plugin_flag = self._strategy_flag._precision_plugin
            if self._strategy_flag._checkpoint_io:
                if self.checkpoint_io:
                    raise MisconfigurationException(
                        "checkpoint_io set through both strategy class and plugins, choose one"
                    )
                self.checkpoint_io = self._strategy_flag._checkpoint_io
            if getattr(self._strategy_flag, "cluster_environment", None):
                if self._cluster_environment_flag:
                    raise MisconfigurationException(
                        "cluster_environment set through both strategy class and plugins, choose one"
                    )
                self._cluster_environment_flag = getattr(self._strategy_flag, "cluster_environment")

            if hasattr(self._strategy_flag, "parallel_devices") and self._strategy_flag.parallel_devices:
                if self._strategy_flag.parallel_devices[0].type == "cpu":
                    if self._accelerator_flag and self._accelerator_flag not in ("auto", "cpu"):
                        raise MisconfigurationException(

View on GitHub (pinned to 9fed5c27d2)

Solutions

1. Remove the precision plugin from the plugins list and let the strategy carry it
2. Or unset precision on the strategy instance (pass precision=None / don't set it) and configure via plugins

Example fix

# before
strategy = DDPStrategy(precision_plugin=MixedPrecision("16-mixed"))
trainer = Trainer(strategy=strategy, plugins=[MixedPrecision("16-mixed")])
# after
strategy = DDPStrategy(precision_plugin=MixedPrecision("16-mixed"))
trainer = Trainer(strategy=strategy)

from lightning.pytorch.plugins import Precision
if isinstance(strategy, Strategy) and strategy._precision_plugin:
    plugins = [p for p in plugins if not isinstance(p, Precision)]
trainer = Trainer(strategy=strategy, plugins=plugins)

def precision_double_config(strategy, plugins) -> bool:
    from lightning.pytorch.plugins import Precision
    return bool(getattr(strategy, "_precision_plugin", None)) and any(isinstance(p, Precision) for p in (plugins or []))

When it happens

Trigger: Trainer(strategy=strategy_with_precision, plugins=[MixedPrecision('16-mixed')]) where the strategy instance was constructed with a precision plugin.

Common situations: Shared strategy factories that pre-install precision; migrating from configs that specified precision on the strategy while keeping plugins entries.

Related errors

• Received both `precision={precision_flag}` and `plugins={sel
• accelerator set through both strategy class and accelerator
• checkpoint_io set through both strategy class and plugins, c
• cluster_environment set through both strategy class and plug
• precision set through both strategy class and plugins, choos

AI-assisted analysis of Lightning-AI/pytorch-lightning@9fed5c27d2 (2026-08-28). Data as JSON: /api/errors/c0f882e5313d0cbe. Report an issue: GitHub.