code: def subscribe_commit(self, repo_name, branch, from_commit_id=None):
          
          repo = proto.Repo(name=repo_name)
          req = proto.SubscribeCommitRequest(repo=repo, branch=branch)
          if from_commit_id is not None:
              getattr(req, 'from').CopyFrom(proto.Commit(repo=repo, id=from_commit_id))
          res = self.stub.SubscribeCommit(req, metadata=self.metadata)
          return res
docs: SubscribeCommit is like ListCommit but it keeps listening for commits as
          they come in. This returns an iterator Commit objects.
  
          Params:
          * repo_name: Name of the repo.
          * branch: Branch to subscribe to.
          * from_commit_id: Optional. Only commits created since this commit
          are returned.