Load Evaluator (#6942)

Create a `load_evaluators()` function so you don't have to import all
the individual evaluator classes

langchain/evaluation/__init__.py

@@ -1,33 +1,45 @@
-"""Functionality relating to evaluation.
+"""Evaluation chains for grading LLM and Chain outputs.
 
-This module contains off-the-shelf evaluation chains for
-grading the output of LangChain primitives such as LLMs and Chains.
+This module contains off-the-shelf evaluation chains for grading the output of
+LangChain primitives such as language models and chains.
+
+To load an evaluator, you can use the :func:`load_evaluators <langchain.evaluation.loading.load_evaluators>` function with the
+names of the evaluators to load.
+
+To load one of the LangChain HuggingFace datasets, you can use the :func:`load_dataset <langchain.evaluation.loading.load_dataset>` function with the
+name of the dataset to load.
 
 Some common use cases for evaluation include:
 
-- Grading accuracy of a response against ground truth answers: QAEvalChain
-- Comparing the output of two models: PairwiseStringEvalChain
-- Judging the efficacy of an agent's tool usage: TrajectoryEvalChain
-- Checking whether an output complies with a set of criteria: CriteriaEvalChain
+- Grading the accuracy of a response against ground truth answers: :class:`QAEvalChain <langchain.evaluation.qa.eval_chain.QAEvalChain>`
+- Comparing the output of two models: :class:`PairwiseStringEvalChain <langchain.evaluation.comparison.eval_chain.PairwiseStringEvalChain>`
+- Judging the efficacy of an agent's tool usage: :class:`TrajectoryEvalChain <langchain.evaluation.agents.trajectory_eval_chain.TrajectoryEvalChain>`
+- Checking whether an output complies with a set of criteria: :class:`CriteriaEvalChain <langchain.evaluation.criteria.eval_chain.CriteriaEvalChain>`
+
+This module also contains low-level APIs for creating custom evaluators for
+specific evaluation tasks. These include:
 
-This module also contains low level APIs for making more evaluators for your
-custom evaluation task. These include:
-- StringEvaluator: Evaluates an output string against a reference and/or
-    with input context.
-- PairwiseStringEvaluator: Evaluates two strings against each other.
-"""
+- :class:`StringEvaluator <langchain.evaluation.schema.StringEvaluator>`: Evaluate a prediction string against a reference label and/or input context.
+- :class:`PairwiseStringEvaluator <langchain.evaluation.schema.PairwiseStringEvaluator>`: Evaluate two prediction strings against each other.
+    Useful for scoring preferences, measuring similarity between two chain or llm agents, or comparing outputs on similar inputs.
+- :class:`AgentTrajectoryEvaluator <langchain.evaluation.schema.AgentTrajectoryEvaluator>`: Evaluate the full sequence of actions
+    taken by an agent.
 
-from langchain.evaluation.agents.trajectory_eval_chain import TrajectoryEvalChain
+"""  # noqa: E501
+from langchain.evaluation.agents import TrajectoryEvalChain
 from langchain.evaluation.comparison import PairwiseStringEvalChain
-from langchain.evaluation.criteria.eval_chain import CriteriaEvalChain
+from langchain.evaluation.criteria import CriteriaEvalChain
+from langchain.evaluation.loading import load_dataset, load_evaluator, load_evaluators
 from langchain.evaluation.qa import ContextQAEvalChain, CotQAEvalChain, QAEvalChain
 from langchain.evaluation.schema import (
     AgentTrajectoryEvaluator,
+    EvaluatorType,
     PairwiseStringEvaluator,
     StringEvaluator,
 )
 
 __all__ = [
+    "EvaluatorType",
     "PairwiseStringEvalChain",
     "QAEvalChain",
     "CotQAEvalChain",
@@ -36,5 +48,8 @@ __all__ = [
     "PairwiseStringEvaluator",
     "TrajectoryEvalChain",
     "CriteriaEvalChain",
+    "load_evaluators",
+    "load_evaluator",
+    "load_dataset",
     "AgentTrajectoryEvaluator",
 ]

langchain/evaluation/agents/trajectory_eval_chain.py

@@ -7,7 +7,7 @@ chain (LLMChain) to generate the reasoning and scores.
 
 from typing import Any, Dict, List, NamedTuple, Optional, Sequence, Tuple, Union
 
-from pydantic import Field
+from pydantic import Extra, Field
 
 from langchain.base_language import BaseLanguageModel
 from langchain.callbacks.manager import (
@@ -15,14 +15,13 @@ from langchain.callbacks.manager import (
     CallbackManagerForChainRun,
     Callbacks,
 )
-from langchain.chains.base import Chain
 from langchain.chains.llm import LLMChain
 from langchain.chat_models.base import BaseChatModel
 from langchain.evaluation.agents.trajectory_eval_prompt import (
     EVAL_CHAT_PROMPT,
     TOOL_FREE_EVAL_CHAT_PROMPT,
 )
-from langchain.evaluation.schema import AgentTrajectoryEvaluator
+from langchain.evaluation.schema import AgentTrajectoryEvaluator, LLMEvalChain
 from langchain.schema import AgentAction, BaseOutputParser, OutputParserException
 from langchain.tools.base import BaseTool
 
@@ -71,7 +70,7 @@ class TrajectoryOutputParser(BaseOutputParser):
         return TrajectoryEval(score=int(score_str), reasoning=reasoning)
 
 
-class TrajectoryEvalChain(AgentTrajectoryEvaluator, Chain):
+class TrajectoryEvalChain(AgentTrajectoryEvaluator, LLMEvalChain):
     """A chain for evaluating ReAct style agents.
 
     This chain is used to evaluate ReAct style agents by reasoning about
@@ -125,6 +124,11 @@ class TrajectoryEvalChain(AgentTrajectoryEvaluator, Chain):
     return_reasoning: bool = False
     """Whether to return the reasoning along with the score."""
 
+    class Config:
+        """Configuration for the QAEvalChain."""
+
+        extra = Extra.ignore
+
     @property
     def _tools_description(self) -> str:
         """Get the description of the agent tools.

langchain/evaluation/comparison/eval_chain.py

@@ -3,13 +3,13 @@ from __future__ import annotations
 
 from typing import Any, Optional
 
-from pydantic import Field
+from pydantic import Extra, Field
 
 from langchain.base_language import BaseLanguageModel
 from langchain.callbacks.manager import Callbacks
 from langchain.chains.llm import LLMChain
 from langchain.evaluation.comparison.prompt import PROMPT, PROMPT_WITH_REFERENCE
-from langchain.evaluation.schema import PairwiseStringEvaluator
+from langchain.evaluation.schema import LLMEvalChain, PairwiseStringEvaluator
 from langchain.prompts.prompt import PromptTemplate
 from langchain.schema import BaseOutputParser
 
@@ -51,7 +51,7 @@ class PairwiseStringResultOutputParser(BaseOutputParser[dict]):
         }
 
 
-class PairwiseStringEvalChain(PairwiseStringEvaluator, LLMChain):
+class PairwiseStringEvalChain(PairwiseStringEvaluator, LLMEvalChain, LLMChain):
     """A chain for comparing the output of two models.
 
     Example:
@@ -81,6 +81,11 @@ class PairwiseStringEvalChain(PairwiseStringEvaluator, LLMChain):
         default_factory=PairwiseStringResultOutputParser
     )
 
+    class Config:
+        """Configuration for the QAEvalChain."""
+
+        extra = Extra.ignore
+
     @property
     def requires_reference(self) -> bool:
         return "reference" in self.prompt.input_variables

langchain/evaluation/criteria/eval_chain.py

@@ -8,7 +8,7 @@ from langchain.base_language import BaseLanguageModel
 from langchain.chains.constitutional_ai.models import ConstitutionalPrinciple
 from langchain.chains.llm import LLMChain
 from langchain.evaluation.criteria.prompt import PROMPT, PROMPT_WITH_REFERENCES
-from langchain.evaluation.schema import StringEvaluator
+from langchain.evaluation.schema import LLMEvalChain, StringEvaluator
 from langchain.schema import BaseOutputParser, BasePromptTemplate
 
 _SUPPORTED_CRITERIA = {
@@ -60,7 +60,7 @@ CRITERIA_TYPE = Union[
 ]
 
 
-class CriteriaEvalChain(StringEvaluator, LLMChain):
+class CriteriaEvalChain(StringEvaluator, LLMEvalChain, LLMChain):
     """LLM Chain for evaluating runs against criteria.
 
     Parameters

langchain/evaluation/loading.py

@@ -1,8 +1,108 @@
-from typing import Dict, List
+"""Loading datasets and evaluators."""
+from typing import Any, Dict, List, Optional, Sequence, Type
+
+from langchain.base_language import BaseLanguageModel
+from langchain.chains.base import Chain
+from langchain.chat_models.openai import ChatOpenAI
+from langchain.evaluation.agents.trajectory_eval_chain import TrajectoryEvalChain
+from langchain.evaluation.comparison import PairwiseStringEvalChain
+from langchain.evaluation.criteria.eval_chain import CriteriaEvalChain
+from langchain.evaluation.qa import ContextQAEvalChain, CotQAEvalChain, QAEvalChain
+from langchain.evaluation.schema import EvaluatorType, LLMEvalChain
 
 
 def load_dataset(uri: str) -> List[Dict]:
-    from datasets import load_dataset
+    """Load a dataset from the LangChainDatasets HuggingFace org."""
+    try:
+        from datasets import load_dataset
+    except ImportError:
+        raise ImportError(
+            "load_dataset requires the `datasets` package."
+            " Please install with `pip install datasets`"
+        )
 
     dataset = load_dataset(f"LangChainDatasets/{uri}")
     return [d for d in dataset["train"]]
+
+
+_EVALUATOR_MAP: Dict[EvaluatorType, Type[LLMEvalChain]] = {
+    EvaluatorType.QA: QAEvalChain,
+    EvaluatorType.COT_QA: CotQAEvalChain,
+    EvaluatorType.CONTEXT_QA: ContextQAEvalChain,
+    EvaluatorType.PAIRWISE_STRING: PairwiseStringEvalChain,
+    EvaluatorType.AGENT_TRAJECTORY: TrajectoryEvalChain,
+    EvaluatorType.CRITERIA: CriteriaEvalChain,
+}
+
+
+def load_evaluator(
+    evaluator: EvaluatorType,
+    *,
+    llm: Optional[BaseLanguageModel] = None,
+    **kwargs: Any,
+) -> Chain:
+    """Load the requested evaluation chain specified by a string.
+
+    Parameters
+    ----------
+    evaluator : EvaluatorType
+        The type of evaluator to load.
+    llm : BaseLanguageModel, optional
+        The language model to use for evaluation, by default None
+    **kwargs : Any
+        Additional keyword arguments to pass to the evaluator.
+
+    Returns
+    -------
+    Chain
+        The loaded evaluation chain.
+
+    Examples
+    --------
+    >>> llm = ChatOpenAI(model="gpt-4", temperature=0)
+    >>> evaluator = load_evaluator(EvaluatorType.QA, llm=llm)
+    """
+    llm = llm or ChatOpenAI(model="gpt-4", temperature=0)
+    return _EVALUATOR_MAP[evaluator].from_llm(llm=llm, **kwargs)
+
+
+def load_evaluators(
+    evaluators: Sequence[EvaluatorType],
+    *,
+    llm: Optional[BaseLanguageModel] = None,
+    config: Optional[dict] = None,
+    **kwargs: Any,
+) -> List[Chain]:
+    """Load evaluators specified by a list of evaluator types.
+
+    Parameters
+    ----------
+    evaluators : Sequence[EvaluatorType]
+        The list of evaluator types to load.
+    llm : BaseLanguageModel, optional
+        The language model to use for evaluation, if none is provided, a default
+        ChatOpenAI gpt-4 model will be used.
+    config : dict, optional
+        A dictionary mapping evaluator types to additional keyword arguments,
+        by default None
+    **kwargs : Any
+        Additional keyword arguments to pass to all evaluators.
+
+    Returns
+    -------
+    List[Chain]
+        The loaded evaluators.
+
+    Examples
+    --------
+    .. code-block:: python
+        from langchain.evaluation import load_evaluators, EvaluatorType
+        evaluators = [EvaluatorType.QA, EvaluatorType.CRITERIA]
+        loaded_evaluators = load_evaluators(evaluators, criteria="helpfulness")
+    """
+    llm = llm or ChatOpenAI(model="gpt-4", temperature=0)
+    loaded = []
+    for evaluator in evaluators:
+        _kwargs = config.get(evaluator, {}) if config else {}
+        loaded.append(load_evaluator(evaluator, llm=llm, **{**kwargs, **_kwargs}))
+    return loaded

langchain/evaluation/qa/eval_chain.py

@@ -3,12 +3,14 @@ from __future__ import annotations
 
 from typing import Any, List, Optional, Sequence
 
+from pydantic import Extra
+
 from langchain import PromptTemplate
 from langchain.base_language import BaseLanguageModel
 from langchain.callbacks.manager import Callbacks
 from langchain.chains.llm import LLMChain
 from langchain.evaluation.qa.eval_prompt import CONTEXT_PROMPT, COT_PROMPT, PROMPT
-from langchain.evaluation.schema import StringEvaluator
+from langchain.evaluation.schema import LLMEvalChain, StringEvaluator
 
 
 def _parse_string_eval_output(text: str) -> dict:
@@ -39,9 +41,14 @@ def _parse_string_eval_output(text: str) -> dict:
     }
 
 
-class QAEvalChain(LLMChain, StringEvaluator):
+class QAEvalChain(LLMChain, StringEvaluator, LLMEvalChain):
     """LLM Chain specifically for evaluating question answering."""
 
+    class Config:
+        """Configuration for the QAEvalChain."""
+
+        extra = Extra.ignore
+
     @property
     def requires_reference(self) -> bool:
         return True
@@ -143,7 +150,7 @@ class QAEvalChain(LLMChain, StringEvaluator):
         return _parse_string_eval_output(result["text"])
 
 
-class ContextQAEvalChain(LLMChain, StringEvaluator):
+class ContextQAEvalChain(LLMChain, StringEvaluator, LLMEvalChain):
     """LLM Chain specifically for evaluating QA w/o GT based on context"""
 
     @property

langchain/evaluation/schema.py

@@ -3,14 +3,47 @@ from __future__ import annotations
 
 import logging
 from abc import ABC, abstractmethod
+from enum import Enum
 from typing import Any, Optional, Sequence, Tuple
 from warnings import warn
 
+from langchain.base_language import BaseLanguageModel
+from langchain.chains.base import Chain
 from langchain.schema.agent import AgentAction
 
 logger = logging.getLogger(__name__)
 
 
+class EvaluatorType(str, Enum):
+    """The types of the evaluators."""
+
+    QA = "qa"
+    """Question answering evaluator, which grades answers to questions
+    directly using an LLM."""
+    COT_QA = "cot_qa"
+    """Chain of thought question answering evaluator, which grades
+    answers to questions using
+    chain of thought 'reasoning'."""
+    CONTEXT_QA = "context_qa"
+    """Question answering evaluator that incorporates 'context' in the response."""
+    PAIRWISE_STRING = "pairwise_string"
+    """The pairwise string evaluator, which compares the output of two models."""
+    AGENT_TRAJECTORY = "trajectory"
+    """The agent trajectory evaluator, which grades the agent's intermediate steps."""
+    CRITERIA = "criteria"
+    """The criteria evaluator, which evaluates a model based on a
+    custom set of criteria."""
+
+
+class LLMEvalChain(Chain):
+    """A base class for evaluators that use an LLM."""
+
+    @classmethod
+    @abstractmethod
+    def from_llm(cls, llm: BaseLanguageModel, **kwargs: Any) -> LLMEvalChain:
+        """Create a new evaluator from an LLM."""
+
+
 class _EvalArgsMixin:
     """Mixin for checking evaluation arguments."""
 

tests/unit_tests/evaluation/test_loading.py

@@ -0,0 +1,16 @@
+"""Test the loading function for evalutors."""
+
+import pytest
+
+from langchain.evaluation.loading import EvaluatorType, load_evaluators
+from tests.unit_tests.llms.fake_chat_model import FakeChatModel
+
+
+@pytest.mark.parametrize("evaluator_type", EvaluatorType)
+def test_load_evaluators(evaluator_type: EvaluatorType) -> None:
+    """Test loading evaluators."""
+    fake_llm = FakeChatModel()
+    load_evaluators([evaluator_type], llm=fake_llm)
+
+    # Test as string
+    load_evaluators([evaluator_type.value], llm=fake_llm)  # type: ignore