code: def _validate_index(self, index):
      if index < 0 or index >= self.nblocks:
          raise ValueError("invalid block index %s" % index)
  
imports: import os
  import re
  import shlex
  import sys
  import pygments
  from pathlib import Path
  from IPython.utils.text import marquee
  from IPython.utils import openpy
  from IPython.utils import py3compat
label_desc: Use image node_id 5 for calling the Demo obj's underlying member method code with example usage: obj._validate_index(index) without return types