core: Add async methods to BaseExampleSelector and SemanticSimilarityExampleSelector (#19399)

Few-Shot prompt template may use a `SemanticSimilarityExampleSelector`
that in turn uses a `VectorStore` that does I/O operations.
So to work correctly on the event loop, we need:
* async methods for the `VectorStore` (OK)
* async methods for the `SemanticSimilarityExampleSelector` (this PR)
* async methods for `BasePromptTemplate` and `BaseChatPromptTemplate`
(future work)

libs/core/langchain_core/example_selectors/base.py

@@ -2,6 +2,8 @@
 from abc import ABC, abstractmethod
 from typing import Any, Dict, List
 
+from langchain_core.runnables import run_in_executor
+
 
 class BaseExampleSelector(ABC):
     """Interface for selecting examples to include in prompts."""
@@ -10,6 +12,14 @@ class BaseExampleSelector(ABC):
     def add_example(self, example: Dict[str, str]) -> Any:
         """Add new example to store."""
 
+    async def aadd_example(self, example: Dict[str, str]) -> Any:
+        """Add new example to store."""
+        return await run_in_executor(None, self.add_example, example)
+
     @abstractmethod
     def select_examples(self, input_variables: Dict[str, str]) -> List[dict]:
         """Select which examples to use based on the inputs."""
+
+    async def aselect_examples(self, input_variables: Dict[str, str]) -> List[dict]:
+        """Select which examples to use based on the inputs."""
+        return await run_in_executor(None, self.select_examples, input_variables)

libs/core/langchain_core/example_selectors/semantic_similarity.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 
 from typing import TYPE_CHECKING, Any, Dict, List, Optional, Type
 
+from langchain_core.documents import Document
 from langchain_core.example_selectors.base import BaseExampleSelector
 from langchain_core.pydantic_v1 import BaseModel, Extra
 from langchain_core.vectorstores import VectorStore
@@ -37,34 +38,59 @@ class SemanticSimilarityExampleSelector(BaseExampleSelector, BaseModel):
         extra = Extra.forbid
         arbitrary_types_allowed = True
 
+    @staticmethod
+    def _example_to_text(
+        example: Dict[str, str], input_keys: Optional[List[str]]
+    ) -> str:
+        if input_keys:
+            return " ".join(sorted_values({key: example[key] for key in input_keys}))
+        else:
+            return " ".join(sorted_values(example))
+
+    def _documents_to_examples(self, documents: List[Document]) -> List[dict]:
+        # Get the examples from the metadata.
+        # This assumes that examples are stored in metadata.
+        examples = [dict(e.metadata) for e in documents]
+        # If example keys are provided, filter examples to those keys.
+        if self.example_keys:
+            examples = [{k: eg[k] for k in self.example_keys} for eg in examples]
+        return examples
+
     def add_example(self, example: Dict[str, str]) -> str:
         """Add new example to vectorstore."""
-        if self.input_keys:
-            string_example = " ".join(
-                sorted_values({key: example[key] for key in self.input_keys})
-            )
-        else:
-            string_example = " ".join(sorted_values(example))
-        ids = self.vectorstore.add_texts([string_example], metadatas=[example])
+        ids = self.vectorstore.add_texts(
+            [self._example_to_text(example, self.input_keys)], metadatas=[example]
+        )
+        return ids[0]
+
+    async def aadd_example(self, example: Dict[str, str]) -> str:
+        """Add new example to vectorstore."""
+        ids = await self.vectorstore.aadd_texts(
+            [self._example_to_text(example, self.input_keys)], metadatas=[example]
+        )
         return ids[0]
 
     def select_examples(self, input_variables: Dict[str, str]) -> List[dict]:
         """Select which examples to use based on semantic similarity."""
         # Get the docs with the highest similarity.
-        if self.input_keys:
-            input_variables = {key: input_variables[key] for key in self.input_keys}
         vectorstore_kwargs = self.vectorstore_kwargs or {}
-        query = " ".join(sorted_values(input_variables))
         example_docs = self.vectorstore.similarity_search(
-            query, k=self.k, **vectorstore_kwargs
+            self._example_to_text(input_variables, self.input_keys),
+            k=self.k,
+            **vectorstore_kwargs,
         )
-        # Get the examples from the metadata.
-        # This assumes that examples are stored in metadata.
-        examples = [dict(e.metadata) for e in example_docs]
-        # If example keys are provided, filter examples to those keys.
-        if self.example_keys:
-            examples = [{k: eg[k] for k in self.example_keys} for eg in examples]
-        return examples
+        return self._documents_to_examples(example_docs)
+
+    async def aselect_examples(self, input_variables: Dict[str, str]) -> List[dict]:
+        """Select which examples to use based on semantic similarity."""
+        # Get the docs with the highest similarity.
+        vectorstore_kwargs = self.vectorstore_kwargs or {}
+        example_docs = await self.vectorstore.asimilarity_search(
+            self._example_to_text(input_variables, self.input_keys),
+            k=self.k,
+            **vectorstore_kwargs,
+        )
+        return self._documents_to_examples(example_docs)
 
     @classmethod
     def from_examples(
@@ -95,13 +121,7 @@ class SemanticSimilarityExampleSelector(BaseExampleSelector, BaseModel):
         Returns:
             The ExampleSelector instantiated, backed by a vector store.
         """
-        if input_keys:
-            string_examples = [
-                " ".join(sorted_values({k: eg[k] for k in input_keys}))
-                for eg in examples
-            ]
-        else:
-            string_examples = [" ".join(sorted_values(eg)) for eg in examples]
+        string_examples = [cls._example_to_text(eg, input_keys) for eg in examples]
         vectorstore = vectorstore_cls.from_texts(
             string_examples, embeddings, metadatas=examples, **vectorstore_cls_kwargs
         )
@@ -113,6 +133,47 @@ class SemanticSimilarityExampleSelector(BaseExampleSelector, BaseModel):
             vectorstore_kwargs=vectorstore_kwargs,
         )
 
+    @classmethod
+    async def afrom_examples(
+        cls,
+        examples: List[dict],
+        embeddings: Embeddings,
+        vectorstore_cls: Type[VectorStore],
+        k: int = 4,
+        input_keys: Optional[List[str]] = None,
+        *,
+        example_keys: Optional[List[str]] = None,
+        vectorstore_kwargs: Optional[dict] = None,
+        **vectorstore_cls_kwargs: Any,
+    ) -> SemanticSimilarityExampleSelector:
+        """Create k-shot example selector using example list and embeddings.
+
+        Reshuffles examples dynamically based on query similarity.
+
+        Args:
+            examples: List of examples to use in the prompt.
+            embeddings: An initialized embedding API interface, e.g. OpenAIEmbeddings().
+            vectorstore_cls: A vector store DB interface class, e.g. FAISS.
+            k: Number of examples to select
+            input_keys: If provided, the search is based on the input variables
+                instead of all variables.
+            vectorstore_cls_kwargs: optional kwargs containing url for vector store
+
+        Returns:
+            The ExampleSelector instantiated, backed by a vector store.
+        """
+        string_examples = [cls._example_to_text(eg, input_keys) for eg in examples]
+        vectorstore = await vectorstore_cls.afrom_texts(
+            string_examples, embeddings, metadatas=examples, **vectorstore_cls_kwargs
+        )
+        return cls(
+            vectorstore=vectorstore,
+            k=k,
+            input_keys=input_keys,
+            example_keys=example_keys,
+            vectorstore_kwargs=vectorstore_kwargs,
+        )
+
 
 class MaxMarginalRelevanceExampleSelector(SemanticSimilarityExampleSelector):
     """ExampleSelector that selects examples based on Max Marginal Relevance.

libs/core/tests/unit_tests/example_selectors/test_base.py

@@ -0,0 +1,26 @@
+from typing import Dict, List, Optional
+
+from langchain_core.example_selectors import BaseExampleSelector
+
+
+class DummyExampleSelector(BaseExampleSelector):
+    def __init__(self) -> None:
+        self.example: Optional[Dict[str, str]] = None
+
+    def add_example(self, example: Dict[str, str]) -> None:
+        self.example = example
+
+    def select_examples(self, input_variables: Dict[str, str]) -> List[dict]:
+        return [input_variables]
+
+
+async def test_aadd_example() -> None:
+    selector = DummyExampleSelector()
+    await selector.aadd_example({"foo": "bar"})
+    assert selector.example == {"foo": "bar"}
+
+
+async def test_aselect_examples() -> None:
+    selector = DummyExampleSelector()
+    examples = await selector.aselect_examples({"foo": "bar"})
+    assert examples == [{"foo": "bar"}]

libs/core/tests/unit_tests/example_selectors/test_similarity.py

@@ -0,0 +1,139 @@
+from typing import Any, Iterable, List, Optional, cast
+
+from langchain_core.documents import Document
+from langchain_core.embeddings import Embeddings, FakeEmbeddings
+from langchain_core.example_selectors import SemanticSimilarityExampleSelector
+from langchain_core.vectorstores import VectorStore
+
+
+class DummyVectorStore(VectorStore):
+    def __init__(self, init_arg: Optional[str] = None):
+        self.texts: List[str] = []
+        self.metadatas: List[dict] = []
+        self._embeddings: Optional[Embeddings] = None
+        self.init_arg = init_arg
+
+    @property
+    def embeddings(self) -> Optional[Embeddings]:
+        return self._embeddings
+
+    def add_texts(
+        self,
+        texts: Iterable[str],
+        metadatas: Optional[List[dict]] = None,
+        **kwargs: Any,
+    ) -> List[str]:
+        self.texts.extend(texts)
+        if metadatas:
+            self.metadatas.extend(metadatas)
+        return ["dummy_id"]
+
+    def similarity_search(
+        self, query: str, k: int = 4, **kwargs: Any
+    ) -> List[Document]:
+        return [
+            Document(page_content=query, metadata={"metadata": query, "other": "other"})
+        ] * k
+
+    @classmethod
+    def from_texts(
+        cls,
+        texts: List[str],
+        embedding: Embeddings,
+        metadatas: Optional[List[dict]] = None,
+        **kwargs: Any,
+    ) -> "DummyVectorStore":
+        store = DummyVectorStore(**kwargs)
+        store.add_texts(texts, metadatas)
+        store._embeddings = embedding
+        return store
+
+
+def test_add_example() -> None:
+    vector_store = DummyVectorStore()
+    selector = SemanticSimilarityExampleSelector(
+        vectorstore=vector_store, input_keys=["foo", "foo3"]
+    )
+    selector.add_example({"foo": "bar", "foo2": "bar2", "foo3": "bar3"})
+    assert vector_store.texts == ["bar bar3"]
+    assert vector_store.metadatas == [{"foo": "bar", "foo2": "bar2", "foo3": "bar3"}]
+
+
+async def test_aadd_example() -> None:
+    vector_store = DummyVectorStore()
+    selector = SemanticSimilarityExampleSelector(
+        vectorstore=vector_store, input_keys=["foo", "foo3"]
+    )
+    await selector.aadd_example({"foo": "bar", "foo2": "bar2", "foo3": "bar3"})
+    assert vector_store.texts == ["bar bar3"]
+    assert vector_store.metadatas == [{"foo": "bar", "foo2": "bar2", "foo3": "bar3"}]
+
+
+def test_select_examples() -> None:
+    vector_store = DummyVectorStore()
+    selector = SemanticSimilarityExampleSelector(
+        vectorstore=vector_store, input_keys=["foo2"], example_keys=["metadata"], k=2
+    )
+    examples = selector.select_examples({"foo": "bar", "foo2": "bar2"})
+    assert examples == [{"metadata": "bar2"}] * 2
+
+
+async def test_aselect_examples() -> None:
+    vector_store = DummyVectorStore()
+    selector = SemanticSimilarityExampleSelector(
+        vectorstore=vector_store, input_keys=["foo2"], example_keys=["metadata"], k=2
+    )
+    examples = await selector.aselect_examples({"foo": "bar", "foo2": "bar2"})
+    assert examples == [{"metadata": "bar2"}] * 2
+
+
+def test_from_examples() -> None:
+    examples = [{"foo": "bar"}]
+    embeddings = FakeEmbeddings(size=1)
+    selector = SemanticSimilarityExampleSelector.from_examples(
+        examples=examples,
+        embeddings=embeddings,
+        vectorstore_cls=DummyVectorStore,
+        k=2,
+        input_keys=["foo"],
+        example_keys=["some_example_key"],
+        vectorstore_kwargs={"vs_foo": "vs_bar"},
+        init_arg="some_init_arg",
+    )
+    assert selector.input_keys == ["foo"]
+    assert selector.example_keys == ["some_example_key"]
+    assert selector.k == 2
+    assert selector.vectorstore_kwargs == {"vs_foo": "vs_bar"}
+
+    assert isinstance(selector.vectorstore, DummyVectorStore)
+    vector_store = cast(DummyVectorStore, selector.vectorstore)
+    assert vector_store.embeddings is embeddings
+    assert vector_store.init_arg == "some_init_arg"
+    assert vector_store.texts == ["bar"]
+    assert vector_store.metadatas == [{"foo": "bar"}]
+
+
+async def test_afrom_examples() -> None:
+    examples = [{"foo": "bar"}]
+    embeddings = FakeEmbeddings(size=1)
+    selector = await SemanticSimilarityExampleSelector.afrom_examples(
+        examples=examples,
+        embeddings=embeddings,
+        vectorstore_cls=DummyVectorStore,
+        k=2,
+        input_keys=["foo"],
+        example_keys=["some_example_key"],
+        vectorstore_kwargs={"vs_foo": "vs_bar"},
+        init_arg="some_init_arg",
+    )
+    assert selector.input_keys == ["foo"]
+    assert selector.example_keys == ["some_example_key"]
+    assert selector.k == 2
+    assert selector.vectorstore_kwargs == {"vs_foo": "vs_bar"}
+
+    assert isinstance(selector.vectorstore, DummyVectorStore)
+    vector_store = cast(DummyVectorStore, selector.vectorstore)
+    assert vector_store.embeddings is embeddings
+    assert vector_store.init_arg == "some_init_arg"
+    assert vector_store.texts == ["bar"]
+    assert vector_store.metadatas == [{"foo": "bar"}]