instantiate.py

# SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: Apache-2.0
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import collections.abc as abc
import dataclasses
import logging
from typing import Any

import attrs

from .registry import _convert_target_to_string, locate

__all__ = ["dump_dataclass", "instantiate"]


def is_dataclass_or_attrs(target):
    return dataclasses.is_dataclass(target) or attrs.has(target)


def dump_dataclass(obj: Any):
    """
    Dump a dataclass recursively into a dict that can be later instantiated.

    Args:
        obj: a dataclass object

    Returns:
        dict
    """
    assert dataclasses.is_dataclass(obj) and not isinstance(
        obj, type
    ), "dump_dataclass() requires an instance of a dataclass."
    ret = {"_target_": _convert_target_to_string(type(obj))}
    for f in dataclasses.fields(obj):
        v = getattr(obj, f.name)
        if dataclasses.is_dataclass(v):
            v = dump_dataclass(v)
        if isinstance(v, (list, tuple)):
            v = [dump_dataclass(x) if dataclasses.is_dataclass(x) else x for x in v]
        ret[f.name] = v
    return ret


def instantiate(cfg, *args, **kwargs):
    """
    Recursively instantiate objects defined in dictionaries by
    "_target_" and arguments.

    Args:
        cfg: a dict-like object with "_target_" that defines the caller, and
            other keys that define the arguments
        args: Optional positional parameters pass-through.
        kwargs: Optional named parameters pass-through.

    Returns:
        object instantiated by cfg
    """
    from omegaconf import DictConfig, ListConfig, OmegaConf

    if isinstance(cfg, ListConfig):
        lst = [instantiate(x) for x in cfg]
        return ListConfig(lst, flags={"allow_objects": True})
    if isinstance(cfg, list):
        # Specialize for list, because many classes take
        # list[objects] as arguments, such as ResNet, DatasetMapper
        return [instantiate(x) for x in cfg]

    # If input is a DictConfig backed by dataclasses (i.e. omegaconf's structured config),
    # instantiate it to the actual dataclass.
    if isinstance(cfg, DictConfig) and is_dataclass_or_attrs(cfg._metadata.object_type):
        return OmegaConf.to_object(cfg)

    if isinstance(cfg, abc.Mapping) and "_target_" in cfg:
        # conceptually equivalent to hydra.utils.instantiate(cfg) with _convert_=all,
        # but faster: https://github.com/facebookresearch/hydra/issues/1200
        cfg = {k: instantiate(v) for k, v in cfg.items()}
        cls = cfg.pop("_target_")
        cls = instantiate(cls)

        if isinstance(cls, str):
            cls_name = cls
            cls = locate(cls_name)
            assert cls is not None, cls_name
        else:
            try:
                cls_name = cls.__module__ + "." + cls.__qualname__
            except Exception:
                # target could be anything, so the above could fail
                cls_name = str(cls)
        assert callable(cls), f"_target_ {cls} does not define a callable object"
        try:
            # override config with kwargs
            instantiate_kwargs = {}
            instantiate_kwargs.update(cfg)
            instantiate_kwargs.update(kwargs)
            return cls(*args, **instantiate_kwargs)
        except TypeError:
            logger = logging.getLogger(__name__)
            logger.error(f"Error when instantiating {cls_name}!")
            raise
    return cfg  # return as-is if don't know what to do