Using Python in Emacs

There are a few things I want when setting up a Python project:

• a virtual environment
• a language server (for use via eglot)
• an interpreter that works well with emacs

To that end, when setting up a project, I follow these steps:

1. Create a new directory for my project, or navigate to an existing project directory.
2. Create a new virtual environment in that directory, with e.g. uv venv -p 3.13 myenv (I tend to use uv for python package/environment management these days).
3. Activate the virtual environment. I use pyvenv and activate environments via pyvenv-activate. Sometimes, I still need to explicitly call source ./myenv/bin/activate in e.g. an open vterm buffer. In general, it's a good idea to make sure the environment is active and running as expected before doing anything.
4. Set up eglot—in your virtual environment, install python-lsp-ruff or ruff-lsp or whatever Python language server provides the functionality you want. It's also worth installing isort if you want to sort your imports with e.g. python-sort-imports.
5. Install and configure gnureadline for native completions (if you get the Warning (python): Your ‘python-shell-interpreter’ doesn’t seem to support readline, yet ‘python-shell-completion-native’ was t and "python3" is not part of the ‘python-shell-completion-native-disabled-interpreters’ list. Native completions have been disabled locally. warning). See here for instructions.
6. Create/open a python buffer and start eglot with M-x eglot.