allow PY in commands, to be replaced with a specific python executable

base.py

@@ -146,11 +146,14 @@ class ServiceManager:
             nr = section.get(self.group)
             if nr is not None:
                 nr = '%02d' % int(nr)
-                self.commands[ins] = command.replace('~', expanduser('~'))
                 services = self.get_services(section)
                 env = {k: get_subs(section, k, ins, nr) for k in section if k.isupper()}
                 result[ins] = services
                 self.env[ins] = env
+                cmd =  command.replace('~', expanduser('~'))
+                if cmd.startswith('PY '):
+                    cmd = env.get('PY', 'python3') + cmd[2:]
+                self.commands[ins] = cmd
         self.info = result
 
     #def get_cmdpats(self, groups):