code: def _init_db(self):
      if self.verbose:
          logger.info("db filename: " + self.fname)
  
      self._session = sqlite3.connect(
          self.fname, isolation_level="EXCLUSIVE"
      )
      with self.readwrite_cursor() as c:
          c.execute(
              "SELECT COUNT(*) FROM sqlite_master WHERE type = 'table'"
          )
          if c.fetchone()[0] == 0:
              logger.debug("create")
              for q in CREATE_QUERIES:
                  c.execute(q)
  
imports: import contextlib
  import getpass
  import logging
  import os
  import sqlite3
  import tempfile
  import warnings
  from io import BytesIO
  from os.path import join
  import numpy
  from nibabel.optpkg import optional_package
  from .nifti1 import Nifti1Header
label_desc: Use image node_id 3 for calling the _DB obj's underlying member method code with example usage: obj._init_db() without return types