How to display current virtualenv in your ZSH Prezto theme

It’s been a few years since I switched from Bash to ZSH on my personal laptop, and I’ve never regretted it. Out of the box, ZSH isn’t that great, but after customizing it using Prezto it’s an amazing timesaver in a lot of little ways.

Oh-My-ZSH is the most well-known ZSH customization framework, but it’s gotten pretty bloated over the years with 200+ plugins, 140+ themes, etc. With that many plugins, some of them are bound to conflict from time to time, and keeping everything straight can be a bit of a mess. It’s also not uncommon for OMZ users who enable a lot of plugins to report shell startup times > 3 seconds, which is annoying.

Prezto started as a fork of Oh-My-ZSH focused on improving performance, and now is an entirely separate project. The Prezto maintainer is a bit gruff and much more inclined to say ‘no’ than ‘yes’ to pull requests, but I see this as a benefit because it minimizes bloat. 95% of the modules that I wanted were already built-in, and it was easy enough to fork the project to add a custom module for the Atom text editor.

Prezto is well-documented, as each module/plugin has its own Readme. Plus there are plenty of blog posts around discussing how to get started with Prezto. Personally, I found it best to just read the Readme for each module, decide which ones I wanted, and enable them. I use Gnu Stow to symlink the .zshrc, .zlogin, and .zpreztorc to my ~/.dotfiles/zsh/ folder and manage them as part of my dotfiles repo.

You can see screenshots of all the default Prezto themes here:

I prefer the Sorin theme, as it strikes a good balance of displaying enough information to be useful without showing so much that its distracting. For example, rather than showing the full path, the prompt only displays the first character of the parent folders. This saves space, focuses the eye on the path name of the current folder, but also doesn’t leave you wondering whether you’re in first_app/requirements/ or second_app/requirements/. Behind the scenes, there are some nice touches such as retrieving Git information asynchronously in the background so it doesn’t slow down the display of the command prompt.

However, the one thing I perpetually missed in the Sorin theme was the active virtualenv – I was always typing which python. So this afternoon I finally sat down and figured out how to customize the theme to display it.

Now, whenever I activate a virtualenv, my prompt changes to:

and it just disappears if there’s no activated virtulaenv.

It’s quite easy if you want to customize your own Prezto theme–just copy the code changes in this commit:

The only tricky part is if you want the virtualenv name on the right hand side, add $python_info[virtualenv] to RPROMPT in line 83, not line 143. I’m not an expert on ZSH scripting, but as best I can tell, this is because Sorin’s theme retrieves the git info asynchronously in the background, and then overwrites the default RPROMPT in 143 with the output from line 83 when the git info returns.

If you want to see the rest of my Prezto customizations, check out my Prezto fork (main change was adding a custom module for as well as my dotfiles repo where I manage my ZSH and Prezto config file customizations.


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