mellea.backends.adapters.adapter

Adapter classes for adding fine-tuned modules to inference backends.

The primary public surface is :func:AdapterMixin.resolve_adapter (find or lazily register an adapter by capability name) and :meth:AdapterMixin._find_adapter (look up a registered adapter). :class:AdapterMixin is mixed into backends that support runtime adapter loading and unloading.

LocalHFAdapter, IntrinsicAdapter, and EmbeddedIntrinsicAdapter are deprecation shims retained for backwards compatibility. They satisfy isinstance(x, _core.Adapter) but delegate all behaviour to the new dataclass. get_adapter_for_intrinsic is similarly deprecated; prefer resolve_adapter.

Functions

FUNC get_adapter_for_intrinsic

get_adapter_for_intrinsic(intrinsic_name: str, intrinsic_adapter_types: list[AdapterType] | tuple[AdapterType, ...], available_adapters: dict[str, T]) -> T | None

Find an adapter from a dict of available adapters based on the adapter function name and its allowed adapter types.

Args:

• intrinsic_name: The name of the adapter function, e.g. "answerability".
• intrinsic_adapter_types: The adapter types allowed for this adapter function, e.g. [AdapterType.ALORA, AdapterType.LORA].
• available_adapters: The available adapters to choose from; maps adapter.qualified_name to the adapter object.

Returns:

• T | None: The first matching adapter found, or None if no match exists.

Classes

CLASS Adapter

An adapter that can be added to a single backend.

An adapter can only be registered with one backend at a time. Use adapter.qualified_name when referencing the adapter after adding it.

Args:

• name: Human-readable name of the adapter.
• adapter_type: Enum describing the adapter type (e.g. AdapterType.LORA or AdapterType.ALORA).

Attributes:

• qualified_name: Unique name used for loading and lookup; formed as "<name>_<adapter_type.value>".
• backend: The backend this adapter has been added to, or None if not yet added.
• path: Filesystem path to the adapter weights; set when the adapter is added to a backend.

CLASS LocalHFAdapter

Abstract adapter subclass for locally loaded Hugging Face model backends.

Subclasses must implement get_local_hf_path to return the filesystem path from which adapter weights should be loaded given a base model name.

Methods:

FUNC get_local_hf_path

get_local_hf_path(self, base_model_name: str) -> str

Return the local filesystem path from which adapter weights should be loaded.

Args:

• base_model_name: The base model name; typically the last component of the Hugging Face model ID (e.g. "granite-4.0-micro").

Returns:

• Filesystem path to the adapter weights directory.

CLASS IntrinsicAdapter

Deprecated shim for adapters that implement adapter functions.

.. deprecated:: Use :class:~mellea.backends.adapters.Adapter directly. IntrinsicAdapter will be removed in a future release (Epic #929, issue #1144).

Subtype of :class:Adapter for models that:

• implement adapter functions
• are packaged as LoRA or aLoRA adapters on top of a base model
• use the shared model loading code in mellea.formatters.granite.intrinsics
• use the shared input and output processing code in mellea.formatters.granite.intrinsics

Args:

• intrinsic_name: Name of the adapter function (e.g. "answerability"); the adapter's qualified_name will be derived from this.
• adapter_type: Enum describing the adapter type; defaults to AdapterType.ALORA.
• config_file: Path to a YAML config file defining the adapter function's I/O transformations; mutually exclusive with config_dict.
• config_dict: Dict defining the adapter function's I/O transformations; mutually exclusive with config_file.
• base_model_name: Base model name used to look up the I/O processing config when neither config_file nor config_dict are provided.

Attributes:

• intrinsic_name: Name of the adapter function this adapter implements.
• intrinsic_metadata: Catalog metadata for the adapter function.
• base_model_name: Base model name provided at construction, if any.
• adapter_type: The adapter type (LORA or ALORA).
• config: Parsed I/O transformation configuration for the adapter function.

.. note:: identity, io_contract, and weights are Phase 1 internal scaffolding populated in __init__ to satisfy the new :class:~mellea.backends.adapters.Adapter protocol. They are not meaningful consumer-facing attributes; io_contract and weights raise :exc:NotImplementedError and will be replaced in Phase 2 (issues #1137, #1141).

Methods:

FUNC get_local_hf_path

get_local_hf_path(self, base_model_name: str) -> str

Return the local filesystem path from which adapter weights should be loaded.

Downloads the adapter weights if they are not already cached locally.

Args:

• base_model_name: The base model name; typically the last component of the Hugging Face model ID (e.g. "granite-3.3-8b-instruct").

Returns:

• Filesystem path to the downloaded adapter weights directory.

FUNC download_and_get_path

download_and_get_path(self, base_model_name: str) -> str

Download the required adapter function files if necessary and return the path to them.

Args:

• base_model_name: the base model; typically the last part of the Hugging Face model id like "granite-3.3-8b-instruct"

Returns:

• a path to the files

CLASS AdapterMixin

Mixin class for backends capable of utilizing adapters.

Three verbs are universal across every adapter reality (LocalFile/PEFT, Embedded/Granite Switch, ServerMediated): base_model_name, add_adapter, and list_adapters. The remaining four verbs are reality-specific — a concrete backend overrides only the verb(s) matching its own reality; the others keep raising NotImplementedError.

Attributes:

• base_model_name: The short model name used to identify adapter variants (e.g. "granite-3.3-8b-instruct" for "ibm-granite/granite-3.3-8b-instruct").

Methods:

FUNC base_model_name

base_model_name(self) -> str

Return the short model name used for adapter variant lookup.

Returns:

• The base model name (e.g. "granite-3.3-8b-instruct").

FUNC add_adapter

add_adapter(self, adapter: AdapterInput) -> None

Register an adapter with this backend so it can be loaded later.

The adapter must not already have been added to a different backend. Concrete backends accept the full AdapterInput union but raise TypeError for adapter realities they do not implement (e.g. a PEFT backend rejects an embedded adapter), so a statically valid call may still be rejected at runtime.

Args:

• adapter: The adapter to register with this backend.

Raises:

• TypeError: If adapter belongs to a reality this backend does not support.

FUNC list_adapters

list_adapters(self) -> list[str]

Return the qualified names of all adapters registered with this backend.

Returns:

• list[str]: Qualified adapter names for all adapters that have been registered via add_adapter.

FUNC load_peft_adapter

load_peft_adapter(self, adapter_qualified_name: str) -> None

Load a previously registered PEFT adapter into the underlying model.

LocalFile/PEFT reality only (e.g. a locally hosted Hugging Face model). The adapter must have been registered via add_adapter before calling this method.

Args:

• adapter_qualified_name: The adapter.qualified_name of the adapter to load.

Raises:

• NotImplementedError: If this backend's adapter reality is not LocalFile/PEFT.

FUNC unload_peft_adapter

unload_peft_adapter(self, adapter_qualified_name: str) -> None

Unload a previously loaded PEFT adapter from the underlying model.

LocalFile/PEFT reality only (e.g. a locally hosted Hugging Face model).

Args:

• adapter_qualified_name: The adapter.qualified_name of the adapter to unload.

Raises:

• NotImplementedError: If this backend's adapter reality is not LocalFile/PEFT.

FUNC activate_peft_adapter

activate_peft_adapter(self, adapter_qualified_name: str) -> None

Switch a previously loaded PEFT adapter on for subsequent generation.

LocalFile/PEFT reality only (e.g. a locally hosted Hugging Face model). The adapter must have been loaded via load_peft_adapter before calling this method.

Args:

• adapter_qualified_name: The adapter.qualified_name of the adapter to activate.

Raises:

• NotImplementedError: If this backend's adapter reality is not LocalFile/PEFT.

FUNC deactivate_peft_adapter

deactivate_peft_adapter(self, adapter_qualified_name: str) -> None

Switch off any active PEFT adapter so generation uses the base model.

LocalFile/PEFT reality only (e.g. a locally hosted Hugging Face model).

Args:

• adapter_qualified_name: The adapter.qualified_name of the adapter to deactivate. Accepted for symmetry with activate_peft_adapter; the underlying primitive clears all active PEFT adapters regardless of name.

Raises:

• NotImplementedError: If this backend's adapter reality is not LocalFile/PEFT.

FUNC render_controls

render_controls(self, adapter_qualified_name: str, active: bool) -> None

Render or clear the control tokens for a baked-in embedded adapter.

Embedded/Granite Switch reality only. Weights are already baked into the model; this only toggles the control-token rendering that activates or deactivates the adapter's behaviour for subsequent requests.

Args:

• adapter_qualified_name: The adapter.qualified_name of the adapter to activate or deactivate.
• active: True to render the adapter's control tokens, False to clear them.

Raises:

• NotImplementedError: If this backend's adapter reality is not Embedded/Granite Switch.

FUNC set_request_adapter

set_request_adapter(self, adapter_qualified_name: str) -> None

Select the adapter to use for the next request.

ServerMediated reality only — for servers that accept an adapter selection per request rather than loading/unloading weights or toggling control tokens locally. No backend implements this reality yet.

Args:

• adapter_qualified_name: The adapter.qualified_name of the adapter to select.

Raises:

• NotImplementedError: Always — the ServerMediated adapter reality has no implementation yet.

FUNC resolve_adapter

resolve_adapter(self, name: str) -> _AdapterCore

Find or lazily register an adapter by capability name.

Default implementation preserves Phase 0 behaviour, using the internal _added_adapters dict that concrete backends maintain. Override in Phase 2 (see epic #929) to implement proper lifecycle management.

Args:

• name: Capability name (e.g. "answerability").

Returns:

• The registered adapter with the given capability.

Raises:

• ValueError: If the backend has no model ID.
• KeyError: If the adapter cannot be found after registration.

FUNC adapter_scope

adapter_scope(self, adapter: '_AdapterCore | None')

Context manager wrapping adapter activation and deactivation.

A no-op when adapter is None. Otherwise: activates adapter.weights, yields, then always deactivates — even if the with body raises. Each phase fires ADAPTER_FUNCTION_PHASE_COMPLETE, and ADAPTER_FUNCTION_INVOCATION_COMPLETE fires on the way out, carrying the overall outcome.

This method fires hooks only; it does not open spans. Span production is a plugin's job (see #1464 for the rule and #1466 for the adapter-function spans), and the ADAPTER_FUNCTION_* family currently has no start hook for a plugin to open a span on. See docs/dev/adapter_observability.md for the metric schema.

deactivate() is guarded on activate()'s own side effect having completed, not on the activate phase's hook dispatch also succeeding. If a plugin subscribed to ADAPTER_FUNCTION_PHASE_COMPLETE raises after activate() already flipped the adapter on, deactivate() still runs — telemetry must not be able to strand the adapter active.

Not atomic across the whole scope: _adapter_activation_lock() is held only inside each of activate()/deactivate()'s own verb calls (see LocalFileBinding.activate), not for the with body in between. Two concurrent adapter_scope() calls on one backend can therefore interleave — one thread's body can run while a different adapter is active, activated by another thread's call. Widening the lock to span the whole scope was tried and reverted: it deadlocks the moment the body does real async generation (confirmed against test_local_file_e2e.py), because that work runs on the shared event-loop thread while this thread holds the lock — a same-thread RLock doesn't help across threads. No caller combines concurrent adapter_scope() calls today (nothing outside tests calls it at all), so this is latent, not reachable — but #1465 (wiring real generation through this scope) has to solve the atomicity and the threading interaction together, not layer one fix on top of the other.

Args:

• adapter: The adapter to activate, or None (no-op).

Raises:

• BaseException: An error raised by activation, the with body, or deactivation. If both the body and deactivation fail, the body error remains primary and the deactivation error is chained.

CLASS EmbeddedIntrinsicAdapter

Deprecated shim for adapter functions embedded in a Granite Switch model.

.. deprecated:: Use :class:~mellea.backends.adapters.Adapter directly. EmbeddedIntrinsicAdapter will be removed in a future release (Epic #929, issue #1144).

Unlike PEFT-based adapters that are loaded into the model at runtime, embedded adapters are already baked into the model weights and activated via control tokens injected by the model's chat template. Only the I/O transformation config (io.yaml) is needed; no adapter weights are downloaded or loaded.

Args:

• intrinsic_name: Name of the adapter function (e.g. "answerability").
• config: Parsed I/O transformation configuration (from io.yaml).
• technology: Adapter technology in the switch model — "lora" or "alora". Determines where the control token is placed in the chat template (beginning of sequence for LoRA, before generation prompt for aLoRA).

Attributes:

• intrinsic_name: Name of the adapter function this adapter implements.
• config: Parsed I/O transformation configuration.
• technology: "lora" or "alora".

.. note:: identity, io_contract, and weights are Phase 1 internal scaffolding populated in __init__ to satisfy the new :class:~mellea.backends.adapters.Adapter protocol. They are not meaningful consumer-facing attributes; io_contract and weights raise :exc:NotImplementedError and will be replaced in Phase 2 (issues #1137, #1142).

Methods:

FUNC from_model_directory

from_model_directory(model_path: str | pathlib.Path, intrinsic_name: str | None = None) -> list['EmbeddedIntrinsicAdapter']

Load embedded adapters from a Granite Switch model directory.

Reads adapter_index.json and the corresponding io_configs/*/io.yaml files from the model directory.

Args:

• model_path: Path to a Granite Switch model directory that contains adapter_index.json and io_configs/.
• intrinsic_name: If provided, only load the adapter matching this adapter function name. None loads all adapters.

Returns:

• list[EmbeddedIntrinsicAdapter]: One adapter per entry in the index.

Raises:

• FileNotFoundError: If adapter_index.json is missing.
• ValueError: If an io.yaml file listed in the index cannot be found or if no adapters are found.

FUNC from_hub

from_hub(repo_id: str, revision: str = 'main', cache_dir: str | None = None, intrinsic_name: str | None = None) -> list['EmbeddedIntrinsicAdapter']

Load embedded adapters from a Granite Switch model on Hugging Face Hub.

Downloads adapter_index.json and the io_configs/ directory, then delegates to :meth:from_model_directory.

Args:

• repo_id: Hugging Face Hub repository ID (e.g. "ibm-granite/granite-switch-micro").
• revision: Git revision to download from.
• cache_dir: Local cache directory; None for the default.
• intrinsic_name: If provided, only load the adapter matching this adapter function name. None loads all adapters.

Returns:

• list[EmbeddedIntrinsicAdapter]: One adapter per entry in the index.

Raises:

• ImportError: If huggingface_hub is not installed.
• PermissionError: If the repository is private or gated and the current Hugging Face credentials do not grant access.
• FileNotFoundError: If the downloaded snapshot has no adapter_index.json (wrong repo/revision, not a Granite Switch model, or a stale cache).
• ValueError: If no adapters are found (delegated from :meth:from_model_directory).

FUNC from_source

from_source(source: str, revision: str = 'main', cache_dir: str | None = None, intrinsic_name: str | None = None) -> list['EmbeddedIntrinsicAdapter']

Load embedded adapters from a local directory or Hugging Face Hub.

Automatically detects whether source is a local filesystem path or a Hugging Face Hub repo ID, and delegates accordingly.

Args:

• source: Local path to a model directory, or a Hugging Face Hub repo ID (e.g. "ibm-granite/granite-switch-micro").
• revision: Git revision (only used for Hub downloads).
• cache_dir: Cache directory (only used for Hub downloads).
• intrinsic_name: If provided, only load the adapter matching this adapter function name. None loads all adapters.

Returns:

• list[EmbeddedIntrinsicAdapter]: One adapter per entry in the index.

CLASS CustomIntrinsicAdapter

Deprecated shim for user-defined custom adapter functions.

.. deprecated:: Use :class:~mellea.backends.adapters.Adapter directly. CustomIntrinsicAdapter will be removed in a future release (Epic #929, issue #1144).

This class has the same functionality as IntrinsicAdapter, except that its constructor monkey-patches Mellea global variables to enable the backend to load the user's adapter.

Args:

• model_id: The Hugging Face model ID used for downloading model weights; expected format is "<user-id>/<repo-name>".
• intrinsic_name: Catalog name for the adapter function; defaults to the repository name portion of model_id if not provided.
• base_model_name: The short name of the base model (NOT its repo ID).