python-lint (#14689)

# Description: _python-lint_

This agent writes Python code that is formatted and linted using
`black`, `ruff`, and `mypy`, but does not execute the code. It writes
the code to a temporary file and then runs the linters. Once these
checks pass, the code is returned.

# Dependencies

- black
- ruff
- mypy

# Demo

The functionality can be seen here:
https://huggingface.co/spaces/joshuasundance/langchain-streamlit-demo

templates/python-lint/README.md

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+# python-lint
+
+This agent specializes in generating high-quality Python code with a focus on proper formatting and linting. It uses `black`, `ruff`, and `mypy` to ensure the code meets standard quality checks.
+
+This streamlines the coding process by integrating and responding to these checks, resulting in reliable and consistent code output.
+
+It cannot actually execute the code it writes, as code execution may introduce additional dependencies and potential security vulnerabilities.
+This makes the agent both a secure and efficient solution for code generation tasks.
+
+You can use it to generate Python code directly, or network it with planning and execution agents.
+
+## Environment Setup
+
+- Install `black`, `ruff`, and `mypy`: `pip install -U black ruff mypy`
+- Set `OPENAI_API_KEY` environment variable.
+
+## Usage
+
+To use this package, you should first have the LangChain CLI installed:
+
+```shell
+pip install -U langchain-cli
+```
+
+To create a new LangChain project and install this as the only package, you can do:
+
+```shell
+langchain app new my-app --package python-lint
+```
+
+If you want to add this to an existing project, you can just run:
+
+```shell
+langchain app add python-lint
+```
+
+And add the following code to your `server.py` file:
+```python
+from python_lint import agent_executor as python_lint_agent
+
+add_routes(app, python_lint_agent, path="/python-lint")
+```
+
+(Optional) Let's now configure LangSmith. 
+LangSmith will help us trace, monitor and debug LangChain applications. 
+LangSmith is currently in private beta, you can sign up [here](https://smith.langchain.com/). 
+If you don't have access, you can skip this section
+
+
+```shell
+export LANGCHAIN_TRACING_V2=true
+export LANGCHAIN_API_KEY=<your-api-key>
+export LANGCHAIN_PROJECT=<your-project>  # if not specified, defaults to "default"
+```
+
+If you are inside this directory, then you can spin up a LangServe instance directly by:
+
+```shell
+langchain serve
+```
+
+This will start the FastAPI app with a server is running locally at 
+[http://localhost:8000](http://localhost:8000)
+
+We can see all templates at [http://127.0.0.1:8000/docs](http://127.0.0.1:8000/docs)
+We can access the playground at [http://127.0.0.1:8000/python-lint/playground](http://127.0.0.1:8000/python-lint/playground)  
+
+We can access the template from code with:
+
+```python
+from langserve.client import RemoteRunnable
+
+runnable = RemoteRunnable("http://localhost:8000/python-lint")
+```