Index: TeXmacs/progs/kernel/library/base.scm
===================================================================
--- TeXmacs/progs/kernel/library/base.scm	(revision 15487)
+++ TeXmacs/progs/kernel/library/base.scm	(working copy)
@@ -325,7 +325,7 @@
   (url->unix u))
 
 (define-public (first-in-path . l)
-  (cond ((null? l) "")
+  (cond ((null? l) #f)
         ((url-exists-in-path? (car l)) (car l))
         (else (apply first-in-path (cdr l)))))
 
Index: plugins/asymptote/progs/init-asymptote.scm
===================================================================
--- plugins/asymptote/progs/init-asymptote.scm	(revision 15487)
+++ plugins/asymptote/progs/init-asymptote.scm	(working copy)
@@ -29,7 +29,7 @@
   (:winpath "Asymptote" ".")
   (:require (url-exists-in-path? "asy"))
   (:require (python-command))
-  (:launch ,(asy-launcher))
+  (:launch ,(and (python-command) (asy-launcher)))
   (:serializer ,asy-serialize)
   (:session "Asymptote")
   (:scripts "Asymptote"))
Index: plugins/dratex/progs/init-dratex.scm
===================================================================
--- plugins/dratex/progs/init-dratex.scm	(revision 15487)
+++ plugins/dratex/progs/init-dratex.scm	(working copy)
@@ -29,6 +29,6 @@
 (plugin-configure dratex
   (:require (python-command))
   (:require (url-exists-in-path? "latex"))
-  (:launch ,(dratex-launcher))
+  (:launch ,(and (python-command) (dratex-launcher)))
   (:serializer ,dratex-serialize)
   (:session "DraTex"))
Index: plugins/eukleides/progs/init-eukleides.scm
===================================================================
--- plugins/eukleides/progs/init-eukleides.scm	(revision 15487)
+++ plugins/eukleides/progs/init-eukleides.scm	(working copy)
@@ -26,7 +26,7 @@
 
 (plugin-configure eukleides
   (:require (url-exists-in-path? "eukleides"))
-  ,@(eukleides-launcher)
+  ,@(if (python-command) (eukleides-launcher) '())
   (:serializer ,eukleides-serialize)
   (:session "Eukleides")
   (:scripts "Eukleides"))
Index: plugins/gnuplot/progs/init-gnuplot.scm
===================================================================
--- plugins/gnuplot/progs/init-gnuplot.scm	(revision 15487)
+++ plugins/gnuplot/progs/init-gnuplot.scm	(working copy)
@@ -31,8 +31,8 @@
   (:winpath "gnuplot" "bin") ;; the first winpath has the highest priority
   (:winpath "GNU Octave/Octave*/mingw64" "bin")
   (:require (url-exists-in-path? "gnuplot"))
-  (:require (url-exists-in-path? (python-command)))
-  ,@(gnuplot-launcher)
+  (:require (and (python-command) (url-exists-in-path? (python-command))))
+  ,@(if (python-command) (gnuplot-launcher) '())
   (:serializer ,gnuplot-serialize)
   (:session "Gnuplot")
   (:scripts "Gnuplot"))
Index: plugins/graph/progs/init-graph.scm
===================================================================
--- plugins/graph/progs/init-graph.scm	(revision 15487)
+++ plugins/graph/progs/init-graph.scm	(working copy)
@@ -26,6 +26,6 @@
 
 (plugin-configure graph
   (:require (python-command))
-  (:launch ,(graph-launcher))
+  (:launch ,(and (python-command) (graph-launcher)))
   (:serializer ,graph-serialize)
   (:session "Graph"))
Index: plugins/graphviz/progs/init-graphviz.scm
===================================================================
--- plugins/graphviz/progs/init-graphviz.scm	(revision 15487)
+++ plugins/graphviz/progs/init-graphviz.scm	(working copy)
@@ -31,6 +31,6 @@
   (:winpath "Graphviz" "bin")
   (:require (url-exists-in-path? "dot"))
   (:require (python-command))
-  (:launch ,(graphviz-launcher))
+  (:launch ,(and (python-command) (graphviz-launcher)))
   (:serializer ,graphviz-serialize)
   (:session "Graphviz"))
Index: plugins/jupyter/progs/init-jupyter.scm
===================================================================
--- plugins/jupyter/progs/init-jupyter.scm	(revision 15487)
+++ plugins/jupyter/progs/init-jupyter.scm	(working copy)
@@ -18,8 +18,9 @@
 ;; Communication with Jupyter
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
+
 (tm-define (check-jupyter?)
-  (and (url-exists-in-path? (python-command))
+  (and (python-command) (url-exists-in-path? (python-command))
        (with cmd (string-append (python-command)
                                 " -m pip show jupyter_client 2> /dev/null")
          (> (string-length (var-eval-system cmd)) 10))))
@@ -27,6 +28,8 @@
 (plugin-configure jupyter  ;; defines supports-jupyter?
   (:require (check-jupyter?)))
 
+(when (python-command)
+
 (define (jupyter-find-kernels)
   (let* ((u "$TEXMACS_PATH/plugins/jupyter/tm_jupyter/kernels.py")
          (cmd (string-append (python-command) " " (system-url->string u)))
@@ -129,3 +132,5 @@
 
 (when (supports-jupyter?)
   (import-from (jupyter-kernels)))
+
+)
Index: plugins/plantuml/progs/init-plantuml.scm
===================================================================
--- plugins/plantuml/progs/init-plantuml.scm	(revision 15487)
+++ plugins/plantuml/progs/init-plantuml.scm	(working copy)
@@ -30,7 +30,7 @@
 (plugin-configure plantuml
   (:require (url-exists-in-path? "plantuml"))
   (:require (python-command))
-  (:launch ,(plantuml-launcher))
+  (:launch ,(and (python-command) (plantuml-launcher)))
   (:serializer ,plantuml-serialize)
   (:session "PlantUML"))
 
Index: plugins/python/progs/init-python.scm
===================================================================
--- plugins/python/progs/init-python.scm	(revision 15487)
+++ plugins/python/progs/init-python.scm	(working copy)
@@ -54,7 +54,7 @@
   (:winpath "Python*" ".")
   (:winpath "Python/Python*" ".")
   (:require (python-command))
-  (:launch ,(python-launcher))
+  (:launch ,(and (python-command) (python-launcher)))
   (:preferences (supports-jupyter?))
   (:tab-completion #t)
   (:serializer ,python-serialize)
Index: plugins/sympy/progs/init-sympy.scm
===================================================================
--- plugins/sympy/progs/init-sympy.scm	(revision 15487)
+++ plugins/sympy/progs/init-sympy.scm	(working copy)
@@ -27,7 +27,7 @@
 
 (plugin-configure sympy
   (:require (python-command))
-  (:launch ,(sympy-launcher))
+  (:launch ,(and (python-command) (sympy-launcher)))
   (:serializer ,sympy-serialize)
   (:tab-completion #t)
   (:session "SymPy"))
Index: plugins/tikz/progs/init-tikz.scm
===================================================================
--- plugins/tikz/progs/init-tikz.scm	(revision 15487)
+++ plugins/tikz/progs/init-tikz.scm	(working copy)
@@ -28,7 +28,7 @@
 (plugin-configure tikz
   (:require (python-command))
   (:require (url-exists-in-path? "latex"))
-  (:launch ,(tikz-launcher))
+  (:launch ,(and (python-command) (tikz-launcher)))
   (:serializer ,tikz-serialize)
   (:session "TikZ"))
 
Index: plugins/xypic/progs/init-xypic.scm
===================================================================
--- plugins/xypic/progs/init-xypic.scm	(revision 15487)
+++ plugins/xypic/progs/init-xypic.scm	(working copy)
@@ -34,6 +34,6 @@
 (plugin-configure xypic
   (:require (python-command))
   (:require (xypic-exists?))
-  (:launch ,(xypic-launcher))
+  (:launch ,(and (python-command) (xypic-launcher)))
   (:serializer ,xypic-serialize)
   (:session "XYpic"))