code: def get_against():
      
      global __cached_against
      if __cached_against is not None:
          return __cached_against
  
      status = subprocess.call(["git", "rev-parse", "--verify", "HEAD"],
                               stdout=open(os.devnull, 'w'),
                               stderr=subprocess.STDOUT)
      if not status:
          against = 'HEAD'
      else:
  	# Initial commit: diff against an empty tree object
          against = '4b825dc642cb6eb9a060e54bf8d69288fbee4904'
  
      __cached_against = against
      return against
docs: Determines the revision against which the staged data ought to be checked.
  
      :returns: The revision.
      :rtype: :class:`str`