code: def pack_zero(self, file_id, number, length=4):
      number = str(number)
      return file_id + "_" + "0" * (length - len(number)) + number
  
imports: import argparse
  import math
  import os
  import sys
  import music21
  from espnet2.fileio.score_scp import SingingScoreWriter, XMLReader
label_desc: Use image node_id 7 for calling the DataHandler obj's underlying member method code with example usage: obj.pack_zero(file_id, number, length) and returns: unknown