diff --git a/.dir-locals.el b/.dir-locals.el
index 3ac0cfc6f0..5187161942 100644
--- a/.dir-locals.el
+++ b/.dir-locals.el
@@ -1,2 +1,8 @@
 ((c-mode . ((c-file-style . "stroustrup")
-	    (indent-tabs-mode . nil))))
+	    (indent-tabs-mode . nil)))
+ (python-mode .
+              ((eval . (when-let* ((root (locate-dominating-file default-directory ".dir-locals.el")))
+                         (setq-local process-environment (copy-sequence process-environment))
+                         (setenv "PYTHONPATH"
+                                 (concat (expand-file-name "python" root) ":"
+                                         (expand-file-name "tests/functional" root))))))))