start-jupyter: load python3/unstable module if no include file is given

start-jupyter

 #!/bin/bash
 #
-# Copyright 2019 Deutsches Klimarechenzentrum GmbH
+# Copyright 2020 Deutsches Klimarechenzentrum GmbH
 #
 # All rights reserved.
 #
@@ -37,7 +37,7 @@
 # DKRZ's mistral nodes. The script then opens a ssh tunnel to connect
 # your local browser to jupyter.
 #
-# If you indicate an account with the -A switch, the script will run
+# If you indicate an account with the -A option, the script will run
 # jupyter in a job on dedicated resources. Otherwise jupyter uses a
 # shared interactive node.
 #
@@ -83,7 +83,8 @@ SJ_PARTITION=shared
 #
 # If indicated, this file will be sourced prior to running jupyter
 # notebook. It has to be located on mistral. Set up the environment
-# for starting the correct jupyter here.
+# for starting the correct jupyter here. If no SJ_INCFILE is given,
+# the module python3/unstable is loaded.
 SJ_INCFILE=""
 
 # Frontend host
@@ -194,6 +195,8 @@ function source_incfile() {
             incfile="\${HOME}/${incfile}"
         fi
         commandline="source ${incfile}; ${commandline}"
+    else
+        commandline="module load python3/unstable; ${commandline}"
     fi
     echo "${commandline}"
 }