Returns the ID for the current user, creating the row if needed.

def _maybe_init_user(self):
    """Returns the ID for the current user, creating the row if needed."""
    user_name = os.environ.get('USER', '') or os.environ.get('USERNAME', '')
    cursor = self._db.cursor()
    cursor.execute('SELECT user_id FROM Users WHERE user_name = ?',
                   (user_name,))
    row = cursor.fetchone()
    if row:
      return row[0]
    user_id = self._create_id()
    cursor.execute(
        """
        INSERT INTO USERS (user_id, user_name, inserted_time)
        VALUES (?, ?, ?)
        """,
        (user_id, user_name, time.time()))
    return user_id