src/HOL/Tools/Sledgehammer/sledgehammer_mash.ML

     val cmd_path = Path.explode cmd_file
     val model_dir = File.shell_path (mash_model_dir ())
     val core = "--inputFile " ^ cmd_file ^ " --predictions " ^ sugg_file
     val command =
       "cd \"$ISABELLE_SLEDGEHAMMER_MASH\"/src; \
-      \python -B ./mash.py --quiet\
+      \PYTHONDONTWRITEBYTECODE=y ./mash.py --quiet\
       \ --outputDir " ^ model_dir ^
       " --modelFile=" ^ model_dir ^ "/model.pickle\
       \ --dictsFile=" ^ model_dir ^ "/dict.pickle\
       \ --log " ^ log_file ^ " " ^ core ^
       (if extra_args = [] then "" else " " ^ space_implode " " extra_args) ^