Emacs: use f5 to find a tox.ini and run it

gistfile1.el

(require 'compile)

(defun* get-closest-pathname (&optional (file "tox.ini"))
  "Determine the pathname of the first instance of FILE starting
from the current directory towards root.  This may not do the
correct thing in presence of links. If it does not find FILE,
then it shall return the name of FILE in the current directory,
suitable for creation"
  (let ((root (expand-file-name "/")))
    (expand-file-name file
		      (loop 
			for d = default-directory then (expand-file-name ".." d)
			if (file-exists-p (expand-file-name file d))
			return d
			if (equal d root)
			return nil))))

(add-hook 'python-mode-hook
          (lambda () 
            (set (make-local-variable 'compile-command) 
                 (format "tox -c %s" (get-closest-pathname)))))

(global-set-key (kbd "<f5>") 'compile)