code: def get_presig(self, target, source, env, executor=None):
          
          from SCons.Subst import SUBST_SIG
          cmd = self.cmd_list
          if is_List(cmd):
              cmd = ' '.join(map(str, cmd))
          else:
              cmd = str(cmd)
          if executor:
              return env.subst_target_source(cmd, SUBST_SIG, executor=executor)
          else:
              return env.subst_target_source(cmd, SUBST_SIG, target, source)
docs: Return the signature contents of this action's command line.
  
          This strips $(-$) and everything in between the string,
          since those parts don't affect signatures.