如何處理「finally」塊中的異常？

Question

鑑於以下Python代碼：

# Use impyla package to access Impala 
from impala.dbapi import connect 
import logging 

def process(): 
    conn = connect(host=host, port=port) # Mocking host and port 
    try: 
     cursor = conn.cursor() 
     # Execute query and fetch result 
    except: 
     loggin.error("Task failed with some exception") 
    finally: 
     cursor.close() # Exception here! 
     conn.close() 

到因帕拉連接被創建。但由於Impala超時，cursor.close()出現異常。

鑑於潛在的例外情況，關閉cursor和conn的正確方法是什麼？

Answer 1

你必須嵌套在try塊：

def process(): 
    conn = connect(host=host, port=port) # Mocking host and port 
    try: 
     cursor = conn.cursor() 
     try: 
      # Execute query and fetch result 
     finally: 
      # here cursor may fail 
      cursor.close() 
    except: 
     loggin.error("Task failed with some exception") 
    finally: 
     conn.close() 

爲了避免這樣的嘗試，終於塊，你可以使用with語句來：

def process(): 
    conn = connect(host=host, port=port) # Mocking host and port 
    try: 
     with conn.cursor() as cursor: 
      # Execute query and fetch result 
      # cursor is automatically closed 
    except: 
     loggin.error("Task failed with some exception") 
    finally: 
     conn.close()