Document how to add custom model providers

docs/source/users/index.md

@@ -159,6 +159,96 @@ responsible for all charges they incur when they make API requests. Review your
 provider's pricing information before submitting requests via Jupyter AI.
 :::
 
+### Custom model providers
+
+You can define new providers using the LangChain framework API. Custom providers
+inherit from both `jupyter-ai`'s ``BaseProvider`` and `langchain`'s [``LLM``][LLM].
+You can either import a pre-defined model from [LangChain LLM list][langchain_llms],
+or define a [custom LLM][custom_llm].
+In the example below, we define a provider with two models using
+a dummy ``FakeListLLM`` model, which returns responses from the ``responses``
+keyword argument.
+
+```python
+# my_package/my_provider.py
+from jupyter_ai_magics import BaseProvider
+from langchain.llms import FakeListLLM
+
+
+class MyProvider(BaseProvider, FakeListLLM):
+    id = "my_provider"
+    name = "My Provider"
+    model_id_key = "model"
+    models = [
+        "model_a",
+        "model_b"
+    ]
+    def __init__(self, **kwargs):
+        model = kwargs.get("model_id")
+        kwargs["responses"] = (
+            ["This is a response from model 'a'"]
+            if model == "model_a" else
+            ["This is a response from model 'b'"]
+        )
+        super().__init__(**kwargs)
+```
+
+
+If the new provider inherits from [``BaseChatModel``][BaseChatModel], it will be available
+both in the chat UI and with magic commands. Otherwise, users can only use the new provider
+with magic commands.
+
+To make the new provider available, you need to declare it as an [entry point](https://setuptools.pypa.io/en/latest/userguide/entry_point.html):
+
+```toml
+# my_package/pyproject.toml
+[project]
+name = "my_package"
+version = "0.0.1"
+
+[project.entry-points."jupyter_ai.model_providers"]
+my-provider = "my_provider:MyProvider"
+```
+
+To test that the above minimal provider package works, install it with:
+
+```sh
+# from `my_package` directory
+pip install -e .
+```
+
+Then, restart JupyterLab. You should now see an info message in the log that mentions
+your new provider's `id`:
+
+```
+[I 2023-10-29 13:56:16.915 AiExtension] Registered model provider `my_provider`.
+```
+
+[langchain_llms]: https://api.python.langchain.com/en/latest/api_reference.html#module-langchain.llms
+[custom_llm]: https://python.langchain.com/docs/modules/model_io/models/llms/custom_llm
+[LLM]: https://api.python.langchain.com/en/latest/llms/langchain.llms.base.LLM.html#langchain.llms.base.LLM
+[BaseChatModel]: https://api.python.langchain.com/en/latest/chat_models/langchain.chat_models.base.BaseChatModel.html
+
+
+### Customizing prompt templates
+
+To modify the prompt template for a given format, override the ``get_prompt_template`` method:
+
+```python
+from langchain.prompts import PromptTemplate
+
+
+class MyProvider(BaseProvider, FakeListLLM):
+    # (... properties as above ...)
+    def get_prompt_template(self, format) -> PromptTemplate:
+        if format === "code":
+            return PromptTemplate.from_template(
+                "{prompt}\n\nProduce output as source code only, "
+                "with no text or explanation before or after it."
+            )
+        return super().get_prompt_template(format)
+```
+
 ## The chat interface
 
 The easiest way to get started with Jupyter AI is to use the chat interface.
@@ -689,7 +779,7 @@ Write a poem about C++.
 
 You can also define a custom LangChain chain:
 
-```
+```python
 from langchain.chains import LLMChain
 from langchain.prompts import PromptTemplate
 from langchain.llms import OpenAI

packages/jupyter-ai-magics/jupyter_ai_magics/utils.py

@@ -30,9 +30,10 @@ def get_lm_providers(
     for model_provider_ep in model_provider_eps:
         try:
             provider = model_provider_ep.load()
-        except:
+        except Exception as e:
             log.error(
-                f"Unable to load model provider class from entry point `{model_provider_ep.name}`."
+                f"Unable to load model provider class from entry point `{model_provider_ep.name}`: %s.",
+                e,
             )
             continue
         if not is_provider_allowed(provider.id, restrictions):
@@ -58,9 +59,10 @@ def get_em_providers(
     for model_provider_ep in model_provider_eps:
         try:
             provider = model_provider_ep.load()
-        except:
+        except Exception as e:
             log.error(
-                f"Unable to load embeddings model provider class from entry point `{model_provider_ep.name}`."
+                f"Unable to load embeddings model provider class from entry point `{model_provider_ep.name}`: %s.",
+                e,
             )
             continue
         if not is_provider_allowed(provider.id, restrictions):

packages/jupyter-ai/jupyter_ai/handlers.py

@@ -182,7 +182,7 @@ def broadcast_message(self, message: Message):
             self.chat_history.append(message)
 
     async def on_message(self, message):
-        self.log.debug("Message recieved: %s", message)
+        self.log.debug("Message received: %s", message)
 
         try:
             message = json.loads(message)