def on_cleanup_error(function, path, excinfo):
                click.secho("warning: failed to remove file or directory: {}\n"
                            "please delete it manually.".format(path),
                            fg="red")
def dfs(self,can,cursum,target,res):
        if cursum > target: return 
        if cursum == target: 
            self.result.append(res)
            return 
        for i in xrange(len(can)):
            if not res or res[len(res)-1] <= can[i]:
                self.dfs(can,cursum+can[i],target,res+[can[i]])