added candidate_count for Vertex models (#11729)

- **Description:** added support for `candidate_count` parameter on
Vertex

libs/langchain/langchain/chat_models/vertexai.py

@@ -12,10 +12,7 @@ from langchain.callbacks.manager import (
 from langchain.chat_models.base import BaseChatModel, _generate_from_stream
 from langchain.llms.vertexai import _VertexAICommon, is_codey_model
 from langchain.pydantic_v1 import root_validator
-from langchain.schema import (
-    ChatGeneration,
-    ChatResult,
-)
+from langchain.schema import ChatGeneration, ChatResult
 from langchain.schema.messages import (
     AIMessage,
     AIMessageChunk,
@@ -177,16 +174,22 @@ class ChatVertexAI(_VertexAICommon, BaseChatModel):
 
         question = _get_question(messages)
         history = _parse_chat_history(messages[:-1])
-        params = self._prepare_params(stop=stop, **kwargs)
+        params = self._prepare_params(stop=stop, stream=False, **kwargs)
         examples = kwargs.get("examples", None)
         if examples:
             params["examples"] = _parse_examples(examples)
 
-        chat = self._start_chat(history, params)
-        response = chat.send_message(question.content)
-        return ChatResult(
-            generations=[ChatGeneration(message=AIMessage(content=response.text))]
-        )
+        msg_params = {}
+        if "candidate_count" in params:
+            msg_params["candidate_count"] = params.pop("candidate_count")
+
+        chat = self._start_chat(history, **params)
+        response = chat.send_message(question.content, **msg_params)
+        generations = [
+            ChatGeneration(message=AIMessage(content=r.text))
+            for r in response.candidates
+        ]
+        return ChatResult(generations=generations)
 
     async def _agenerate(
         self,
@@ -219,11 +222,16 @@ class ChatVertexAI(_VertexAICommon, BaseChatModel):
         if examples:
             params["examples"] = _parse_examples(examples)
 
-        chat = self._start_chat(history, params)
-        response = await chat.send_message_async(question.content)
-        return ChatResult(
-            generations=[ChatGeneration(message=AIMessage(content=response.text))]
-        )
+        msg_params = {}
+        if "candidate_count" in params:
+            msg_params["candidate_count"] = params.pop("candidate_count")
+        chat = self._start_chat(history, **params)
+        response = await chat.send_message_async(question.content, **msg_params)
+        generations = [
+            ChatGeneration(message=AIMessage(content=r.text))
+            for r in response.candidates
+        ]
+        return ChatResult(generations=generations)
 
     def _stream(
         self,
@@ -239,7 +247,7 @@ class ChatVertexAI(_VertexAICommon, BaseChatModel):
         if examples:
             params["examples"] = _parse_examples(examples)
 
-        chat = self._start_chat(history, params)
+        chat = self._start_chat(history, **params)
         responses = chat.send_message_streaming(question.content, **params)
         for response in responses:
             if run_manager:
@@ -247,11 +255,11 @@ class ChatVertexAI(_VertexAICommon, BaseChatModel):
             yield ChatGenerationChunk(message=AIMessageChunk(content=response.text))
 
     def _start_chat(
-        self, history: _ChatHistory, params: dict
+        self, history: _ChatHistory, **kwargs: Any
     ) -> Union[ChatSession, CodeChatSession]:
         if not self.is_codey_model:
             return self.client.start_chat(
-                context=history.context, message_history=history.history, **params
+                context=history.context, message_history=history.history, **kwargs
             )
         else:
-            return self.client.start_chat(message_history=history.history, **params)
+            return self.client.start_chat(message_history=history.history, **kwargs)

libs/langchain/langchain/llms/vertexai.py

@@ -175,7 +175,10 @@ class _VertexAICommon(_VertexAIBase):
     "The default custom credentials (google.auth.credentials.Credentials) to use "
     "when making API calls. If not provided, credentials will be ascertained from "
     "the environment."
+    n: int = 1
+    """How many completions to generate for each prompt."""
     streaming: bool = False
+    """Whether to stream the results or not."""
 
     @property
     def _llm_type(self) -> str:
@@ -203,6 +206,7 @@ class _VertexAICommon(_VertexAIBase):
                 "max_output_tokens": self.max_output_tokens,
                 "top_k": self.top_k,
                 "top_p": self.top_p,
+                "candidate_count": self.n,
             }
 
     @classmethod
@@ -215,10 +219,16 @@ class _VertexAICommon(_VertexAIBase):
     def _prepare_params(
         self,
         stop: Optional[List[str]] = None,
+        stream: bool = False,
         **kwargs: Any,
     ) -> dict:
         stop_sequences = stop or self.stop
-        return {**self._default_params, "stop_sequences": stop_sequences, **kwargs}
+        params_mapping = {"n": "candidate_count"}
+        params = {params_mapping.get(k, k): v for k, v in kwargs.items()}
+        params = {**self._default_params, "stop_sequences": stop_sequences, **params}
+        if stream or self.streaming:
+            params.pop("candidate_count")
+        return params
 
 
 class VertexAI(_VertexAICommon, BaseLLM):
@@ -260,6 +270,9 @@ class VertexAI(_VertexAICommon, BaseLLM):
                     values["client"] = CodeGenerationModel.from_pretrained(model_name)
         except ImportError:
             raise_vertex_import_error()
+
+        if values["streaming"] and values["n"] > 1:
+            raise ValueError("Only one candidate can be generated with streaming!")
         return values
 
     def _generate(
@@ -271,7 +284,7 @@ class VertexAI(_VertexAICommon, BaseLLM):
         **kwargs: Any,
     ) -> LLMResult:
         should_stream = stream if stream is not None else self.streaming
-        params = self._prepare_params(stop=stop, **kwargs)
+        params = self._prepare_params(stop=stop, stream=should_stream, **kwargs)
         generations = []
         for prompt in prompts:
             if should_stream:
@@ -285,7 +298,7 @@ class VertexAI(_VertexAICommon, BaseLLM):
                 res = completion_with_retry(
                     self, prompt, run_manager=run_manager, **params
                 )
-                generations.append([_response_to_generation(res)])
+                generations.append([_response_to_generation(r) for r in res.candidates])
         return LLMResult(generations=generations)
 
     async def _agenerate(
@@ -301,7 +314,7 @@ class VertexAI(_VertexAICommon, BaseLLM):
             res = await acompletion_with_retry(
                 self, prompt, run_manager=run_manager, **params
             )
-            generations.append([_response_to_generation(res)])
+            generations.append([_response_to_generation(r) for r in res.candidates])
         return LLMResult(generations=generations)
 
     def _stream(
@@ -311,7 +324,7 @@ class VertexAI(_VertexAICommon, BaseLLM):
         run_manager: Optional[CallbackManagerForLLMRun] = None,
         **kwargs: Any,
     ) -> Iterator[GenerationChunk]:
-        params = self._prepare_params(stop=stop, **kwargs)
+        params = self._prepare_params(stop=stop, stream=True, **kwargs)
         for stream_resp in stream_completion_with_retry(
             self, prompt, run_manager=run_manager, **params
         ):

libs/langchain/langchain/utilities/vertexai.py

@@ -5,7 +5,7 @@ if TYPE_CHECKING:
     from google.auth.credentials import Credentials
 
 
-def raise_vertex_import_error(minimum_expected_version: str = "1.33.0") -> None:
+def raise_vertex_import_error(minimum_expected_version: str = "1.35.0") -> None:
     """Raise ImportError related to Vertex SDK being not available.
 
     Args:

libs/langchain/tests/integration_tests/chat_models/test_vertexai.py

@@ -20,7 +20,10 @@ from langchain.schema.messages import AIMessage, HumanMessage, SystemMessage
 
 @pytest.mark.parametrize("model_name", [None, "codechat-bison", "chat-bison"])
 def test_vertexai_instantiation(model_name: str) -> None:
-    model = ChatVertexAI(model_name=model_name)
+    if model_name:
+        model = ChatVertexAI(model_name=model_name)
+    else:
+        model = ChatVertexAI()
     assert model._llm_type == "vertexai"
     assert model.model_name == model.client._model_id
 
@@ -38,6 +41,15 @@ def test_vertexai_single_call(model_name: str) -> None:
     assert isinstance(response.content, str)
 
 
+def test_candidates() -> None:
+    model = ChatVertexAI(model_name="chat-bison@001", temperature=0.3, n=2)
+    message = HumanMessage(content="Hello")
+    response = model.generate(messages=[[message]])
+    assert isinstance(response, LLMResult)
+    assert len(response.generations) == 1
+    assert len(response.generations[0]) == 2
+
+
 @pytest.mark.scheduled
 @pytest.mark.asyncio
 async def test_vertexai_agenerate() -> None:
@@ -153,7 +165,8 @@ def test_vertexai_args_passed(stop: Optional[str]) -> None:
     with patch(
         "vertexai.language_models._language_models.ChatModel.start_chat"
     ) as start_chat:
-        mock_response = Mock(text=response_text)
+        mock_response = MagicMock()
+        mock_response.candidates = [Mock(text=response_text)]
         mock_chat = MagicMock()
         start_chat.return_value = mock_chat
         mock_send_message = MagicMock(return_value=mock_response)
@@ -167,7 +180,7 @@ def test_vertexai_args_passed(stop: Optional[str]) -> None:
             response = model([message])
 
         assert response.content == response_text
-        mock_send_message.assert_called_once_with(user_prompt)
+        mock_send_message.assert_called_once_with(user_prompt, candidate_count=1)
         expected_stop_sequence = [stop] if stop else None
         start_chat.assert_called_once_with(
             context=None,

libs/langchain/tests/integration_tests/llms/test_vertexai.py

@@ -29,29 +29,31 @@ def test_vertex_call() -> None:
 
 @pytest.mark.scheduled
 def test_vertex_generate() -> None:
-    llm = VertexAI(temperate=0)
-    output = llm.generate(["Please say foo:"])
+    llm = VertexAI(temperature=0.3, n=2, model_name="text-bison@001")
+    output = llm.generate(["Say foo:"])
     assert isinstance(output, LLMResult)
+    assert len(output.generations) == 1
+    assert len(output.generations[0]) == 2
 
 
 @pytest.mark.scheduled
 @pytest.mark.asyncio
 async def test_vertex_agenerate() -> None:
-    llm = VertexAI(temperate=0)
+    llm = VertexAI(temperature=0)
     output = await llm.agenerate(["Please say foo:"])
     assert isinstance(output, LLMResult)
 
 
 @pytest.mark.scheduled
 def test_vertex_stream() -> None:
-    llm = VertexAI(temperate=0)
+    llm = VertexAI(temperature=0)
     outputs = list(llm.stream("Please say foo:"))
     assert isinstance(outputs[0], str)
 
 
 @pytest.mark.asyncio
 async def test_vertex_consistency() -> None:
-    llm = VertexAI(temperate=0)
+    llm = VertexAI(temperature=0)
     output = llm.generate(["Please say foo:"])
     streaming_output = llm.generate(["Please say foo:"], stream=True)
     async_output = await llm.agenerate(["Please say foo:"])