以下代码引发UnboundLocalError：

def fetch_results(conn, sql, **bind_params):
    """
    Immediately fetches the SQL results into memory
    Trades memory for the ability to immediately execute another query
    """
    global _log_func
    try:
        cur = conn.cursor()
        if _log_func:
            _log_func(cur, sql, bind_params)

        cur.execute(sql, bind_params)
        return cur.fetchall()
    finally:
        cur.close()

错误：

line 75, in fetch_results
    cur.close()
UnboundLocalError: local variable 'cur' referenced before assignment

我不知道为什么。有人能指出我正确的方向吗？