I've been using Fish for years and spend my entire day working with Python. Python's virtualenv has an `activate.fish` command, I've never had any problems with it. Additionally, we have a ton of internal tooling built in a fabfile, so I've written a couple of snippets of fish that automatically activate that .venv (Poetry managed) whenever I cd into a directory that has one, and also expands a bunch of env vars into the shell session. I've also got this feature request in on the virtualenv repo in the hope that one day we can have activate.fish emit an event - https://github.com/pypa/virtualenv/issues/1456