How to use the sqlitedict.SqliteDict.VALID_FLAGS function in sqlitedict

Set `journal_mode` to 'OFF' if you're experiencing sqlite I/O problems
        or if you need performance and don't care about crash-consistency.

        The `flag` parameter. Exactly one of:
          'c': default mode, open for read/write, creating the db/table if necessary.
          'w': open for r/w, but drop `tablename` contents first (start with empty table)
          'r': open as read-only
          'n': create a new database (erasing any existing tables, not just `tablename`!).

        """
        self.in_temp = filename is None
        if self.in_temp:
            randpart = hex(random.randint(0, 0xffffff))[2:]
            filename = os.path.join(tempfile.gettempdir(), 'sqldict' + randpart)

        if flag not in SqliteDict.VALID_FLAGS:
            raise RuntimeError("Unrecognized flag: %s" % flag)
        self.flag = flag

        if flag == 'n':
            if os.path.exists(filename):
                os.remove(filename)

        dirname = os.path.dirname(filename)
        if dirname:
            if not os.path.exists(dirname):
                raise RuntimeError('Error! The directory does not exist, %s' % dirname)

        self.filename = filename
        self.tablename = tablename

        logger.info("opening Sqlite table %r in %s" % (tablename, filename))

The `encode` and `decode` parameters are used to customize how the values
        are serialized and deserialized.
        The `encode` parameter must be a function that takes a single Python
        object and returns a serialized representation.
        The `decode` function must be a function that takes the serialized
        representation produced by `encode` and returns a deserialized Python
        object.
        The default is to use pickle.

        """
        self.in_temp = filename is None
        if self.in_temp:
            randpart = hex(random.randint(0, 0xffffff))[2:]
            filename = os.path.join(tempfile.gettempdir(), 'sqldict' + randpart)

        if flag not in SqliteDict.VALID_FLAGS:
            raise RuntimeError("Unrecognized flag: %s" % flag)
        self.flag = flag

        if flag == 'n':
            if os.path.exists(filename):
                os.remove(filename)

        dirname = os.path.dirname(filename)
        if dirname:
            if not os.path.exists(dirname):
                raise RuntimeError('Error! The directory does not exist, %s' % dirname)

        self.filename = filename
        if '"' in tablename:
            raise ValueError('Invalid tablename %r' % tablename)
        self.tablename = tablename