community(you): Integrate You.com conversational APIs (#23046)

You.com is releasing two new conversational APIs — Smart and Research. 

This PR:
- integrates those APIs with Langchain, as an LLM
- streaming is supported

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, ccurme, vbarda, hwchase17.

libs/community/langchain_community/llms/you.py

@@ -0,0 +1,140 @@
+import os
+from typing import Any, Dict, Generator, Iterator, List, Literal, Optional
+
+import requests
+from langchain_core.callbacks.manager import CallbackManagerForLLMRun
+from langchain_core.language_models.llms import LLM
+from langchain_core.outputs import GenerationChunk
+from langchain_core.pydantic_v1 import Field
+
+SMART_ENDPOINT = "https://chat-api.you.com/smart"
+RESEARCH_ENDPOINT = "https://chat-api.you.com/research"
+
+
+def _request(base_url: str, api_key: str, **kwargs: Any) -> Dict[str, Any]:
+    """
+    NOTE: This function can be replaced by a OpenAPI-generated Python SDK in the future,
+    for better input/output typing support.
+    """
+    headers = {"x-api-key": api_key}
+    response = requests.post(base_url, headers=headers, json=kwargs)
+    response.raise_for_status()
+    return response.json()
+
+
+def _request_stream(
+    base_url: str, api_key: str, **kwargs: Any
+) -> Generator[str, None, None]:
+    headers = {"x-api-key": api_key}
+    params = dict(**kwargs, stream=True)
+    response = requests.post(base_url, headers=headers, stream=True, json=params)
+    response.raise_for_status()
+
+    # Explicitly coercing the response to a generator to satisfy mypy
+    event_source = (bytestring for bytestring in response)
+
+    try:
+        import sseclient
+
+        client = sseclient.SSEClient(event_source)
+    except ImportError:
+        raise ImportError(
+            (
+                "Could not import `sseclient`. "
+                "Please install it with `pip install sseclient-py`."
+            )
+        )
+
+    for event in client.events():
+        if event.event in ("search_results", "done"):
+            pass
+        elif event.event == "token":
+            yield event.data
+        elif event.event == "error":
+            raise ValueError(f"Error in response: {event.data}")
+        else:
+            raise NotImplementedError(f"Unknown event type {event.event}")
+
+
+class You(LLM):
+    """Wrapper around You.com's conversational Smart and Research APIs.
+
+    Each API endpoint is designed to generate conversational
+    responses to a variety of query types, including inline citations
+    and web results when relevant.
+
+    Smart Endpoint:
+    - Quick, reliable answers for a variety of questions
+    - Cites the entire web page URL
+
+    Research Endpoint:
+    - In-depth answers with extensive citations for a variety of questions
+    - Cites the specific web page snippet relevant to the claim
+
+    To connect to the You.com api requires an API key which
+    you can get at https://api.you.com.
+
+    For more information, check out the documentations at
+    https://documentation.you.com/api-reference/.
+
+    Args:
+        endpoint: You.com conversational endpoints. Choose from "smart" or "research"
+        ydc_api_key: You.com API key, if `YDC_API_KEY` is not set in the environment
+    """
+
+    endpoint: Literal["smart", "research"] = Field(
+        "smart",
+        description=(
+            'You.com conversational endpoints. Choose from "smart" or "research"'
+        ),
+    )
+    ydc_api_key: Optional[str] = Field(
+        None,
+        description="You.com API key, if `YDC_API_KEY` is not set in the envrioment",
+    )
+
+    def _call(
+        self,
+        prompt: str,
+        stop: Optional[List[str]] = None,
+        run_manager: Optional[CallbackManagerForLLMRun] = None,
+        **kwargs: Any,
+    ) -> str:
+        if stop:
+            raise NotImplementedError(
+                "Stop words are not implemented for You.com endpoints."
+            )
+        params = {"query": prompt}
+        response = _request(self._request_endpoint, api_key=self._api_key, **params)
+        return response["answer"]
+
+    def _stream(
+        self,
+        prompt: str,
+        stop: Optional[List[str]] = None,
+        run_manager: Optional[CallbackManagerForLLMRun] = None,
+        **kwargs: Any,
+    ) -> Iterator[GenerationChunk]:
+        if stop:
+            raise NotImplementedError(
+                "Stop words are not implemented for You.com endpoints."
+            )
+        params = {"query": prompt}
+        for token in _request_stream(
+            self._request_endpoint, api_key=self._api_key, **params
+        ):
+            yield GenerationChunk(text=token)
+
+    @property
+    def _request_endpoint(self) -> str:
+        if self.endpoint == "smart":
+            return SMART_ENDPOINT
+        return RESEARCH_ENDPOINT
+
+    @property
+    def _api_key(self) -> str:
+        return self.ydc_api_key or os.environ["YDC_API_KEY"]
+
+    @property
+    def _llm_type(self) -> str:
+        return "you.com"