code: def main(branch):
      
      try:
          # Ensure that we're in a git repository. This command is silent unless
          # you're not actually in a git repository, in which case, you receive a
          # "Not a git repository" error message.
          output = subprocess.check_output(['git', 'rev-parse']).decode('utf-8')
          sys.stdout.write(output)
      except subprocess.CalledProcessError:
          # Bail if we're not in a git repository.
          return
  
      # This behavior ensures a better user experience for those that aren't
      # intimately familiar with git.
      ensure_remote_branch_is_tracked(branch)
  
      # Switch to the specified branch and update it.
      subprocess.check_call(['git', 'checkout', '--quiet', branch])
  
      # Pulling is always safe here, because we never commit to this branch.
      subprocess.check_call(['git', 'pull', '--quiet'])
  
      # Checkout the top commit in the branch, effectively going "untracked."
      subprocess.check_call(['git', 'checkout', '--quiet', '%s~0' % branch])
  
      # Clean up the repository of Python cruft. Because we've just switched
      # branches and compiled Python files should not be version controlled,
      # there are likely leftover compiled Python files sitting on disk which may
      # confuse some tools, such as sqlalchemy-migrate.
      subprocess.check_call(['find', '.', '-name', '"*.pyc"', '-delete'])
  
      # For the sake of user experience, give some familiar output.
      print('Your branch is up to date with branch \'origin/%s\'.' % branch)
docs: Checkout, update and branch from the specified branch.