My day job is all about #Python (which I love). Here are some personal rules, specific to working with Python projects:
* Do **not** install or modify global tools, especially Python itself or any packages. This means a given system might not even **have** a global Python
* Always use virtual environments (`uv` agrees with me, and doesn't need this but). I always set the global environment variable `PIP_REQUIRE_VIRTUALENV`.
* The two rules above mean my virtual environment contains (not via a link, it's really there) Python itself (and of course, of the right version)
* Virtual environments always live **inside** a project directory. Never global.
* Activate virtual environments only **inside** the project directory (`direnv` #direnv makes this easy)
* Don't install (let alone use) #Anaconda, #Miniconda, or #Mamba, because those violate all the rules above (but see the next rule)
* Anaconda-based packages implies a `pixi` #Pixi project (it's the same people, but a better answer, and you still get what you want -- the correct packages)
* No Anaconda-based packages implies a `uv` #UV project
* Always use `pyproject.toml` #pyprojecttoml over any other config file (e.g., `requirements.txt` #requirementstxt), except where things just don't work, such as needing `pyrefly.toml`
* `uv`, `pixi`, and `direnv` must exist outside of any project, so install them at the user level, or else globally if and only if that is appropriate and compelling enough to override rule one
That was a wall of text, but in practice doing it this way is trivial. It's probably **less** work than you have been doing. This post is just about managing your Python versions, environments, and projects. Not about, e.g., using `pre-commit` #precommit, or doing type checking, etc. But if you follow these rules, your work will be easier, faster, more adaptable, and encounter fewer obstacles.
