code: def clone(self, repo, ref, deps=()):
          
  
          if os.path.isdir(repo):
              repo = os.path.abspath(repo)
  
          def clone_strategy(directory):
              env = git.no_git_env()
  
              def _git_cmd(*args):
                  cmd_output('git', *args, cwd=directory, env=env)
  
              _git_cmd('init', '.')
              _git_cmd('remote', 'add', 'origin', repo)
  
              try:
                  self._shallow_clone(ref, _git_cmd)
              except CalledProcessError:
                  self._complete_clone(ref, _git_cmd)
  
          return self._new_repo(repo, ref, deps, clone_strategy)
docs: Clone the given url and checkout the specific ref.