Using directory-local variables to customize the emacs project experience

I use emacs for nearly all my editing and interactive analysis. As one typically does, more than one project is the norm, not the exception. Discovering projectile for project-specific buffers and controls, combined with helm for very fast, fuzzy completions, makes emacs a very convenient and efficient environment for most task.

One challenge I ran into was the need to have multiple interactive python buffers, typically one per project. However, the out-of-the-box behavior of python-mode is to have only one python interactive buffer named “Python”. In order to localize the python interactive shell, I found it necessary to assign a custom name to the python buffer and to associate that name with the project. Using directory-local variables turned out to be the trick. It is also the current recommendation from the projectile project for customizing things in the current project.

To set a directory variable, one first needs to know what variable to set. A simple way to see what is available for customization is to perform M-x customize followed by the mode to customize. In this case, python suffices. The variable of interest is the python-shell-buffer-name. With projectile-mode active and in a project, C-c p E will prompt for the variable to customize, in this case python-shell-buffer-name.

Then, supply the custom name. In my case, I am going with the convention of “Python[MyProjectName]”. Note that no * are used around the name. The result will be a new .dir-locals.el file in the project root directory. This new variable will only become active on opening new files; it does not affect previously-opened files. After this process, activating a new python shell will result in that shell taking on the customized name and all python editor buffers in the project will use the same project-specific

The resulting .dir-locals.el file will look like:

;;; Directory Local Variables
;;; For more information see (info "(emacs) Directory Variables")

((python-mode
  (python-shell-buffer-name . "Python[MyProjectName]")))