code: def post(self):
      g_cred_path = self.get_argument("g_cred_path", "")
      valid = op.exists(g_cred_path)
      if valid:
          VizSeqGlobalConfigManager().set_g_cred_path(g_cred_path)
      import json
  
      self.write(json.dumps({"valid": valid}))
  
imports: import os
  import os.path
  import argparse
  from typing import List
  from vizseq._utils.logger import logger
  from vizseq._view import VizSeqWebView, DEFAULT_PAGE_SIZE, DEFAULT_PAGE_NO
  from vizseq._data.zip_file import VizSeqZipFile
  from vizseq._data import get_g_translate, VizSeqGlobalConfigManager
  from vizseq._visualizers import SPAN_HIGHTLIGHT_JS
  from vizseq._utils import VizSeqJson
  from vizseq import __version__
  from tornado import web, ioloop
  from jinja2 import Environment, PackageLoader, select_autoescape
label_desc: Use image node_id 2 for calling the ConfigHandler obj's underlying member method code with example usage: obj.post() without return types