code: def _run(self):
      # when we are running from pre-commit tool, it doesn't provide CLI
      # flags, but instead provides respective env vars that we could use.
      flag = os.environ.get("PRE_COMMIT_CHECKOUT_TYPE")
      if flag is None and len(self.args.args) >= 3:
          # see https://git-scm.com/docs/githooks#_post_checkout
          flag = self.args.args[2]
  
      # checking out some reference and not specific file.
      if flag != "1":
          return 0
  
      # make sure we are not in the middle of a rebase/merge, so we
      # don't accidentally break it with an unsuccessful checkout.
      # Note that git hooks are always running in repo root.
      if os.path.isdir(os.path.join(".git", "rebase-merge")):
          return 0
  
      from dvc.cli import main
  
      return main(["checkout"])
  
imports: import os
  from dvc.cli import formatter
  from dvc.cli.command import CmdBaseNoRepo
  from dvc.exceptions import NotDvcRepoError
  from dvc.log import logger
label_desc: Use image node_id 1 for calling the CmdPostCheckout obj's underlying member method code with example usage: obj._run() and returns: main, int, int