code: def atlasdb_open( path ):
      
      if not os.path.exists(path):
          log.debug("Atlas DB doesn't exist at %s" % path)
          return None
  
      con = sqlite3.connect( path, isolation_level=None )
      con.row_factory = atlasdb_row_factory
      return con
docs: Open the atlas db.
      Return a connection.
      Return None if it doesn't exist