Python-異常處理

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一、捕獲異常

1、當程式出錯時，不會展示bug資訊給使用者，而是提供一個友好的提示後，繼續執行程式

2、如下，實現除法，當分母為0時，捕獲並列印出異常資訊；Exception可以捕獲任何異常

def div(x, y):    try:        print(x/y)    except Exception as e:        print(‘異常為‘, e)

>>> div(1,0)
異常為 division by zero

 

也可以指定異常為ZeroDivisionError

def div(x, y):    try:        print(x/y)    except ZeroDivisionError as e:        print(‘異常為‘, e)

>>> div(1,0)
異常為 division by zero

 

3、同時捕獲多個異常

def fdiv(x,y):    try:        return x/y    except TypeError as e:        print(‘TypeError: ‘, e)    except ZeroDivisionError as e:        print(‘ZeroDivisionError: ‘, e)    except Exception as e:        print(‘其他異常：‘, e)

>>> fdiv(‘ABC‘, 0)
TypeError: unsupported operand type(s) for /: ‘str‘ and ‘int‘
>>> fdiv(12,0)
ZeroDivisionError: division by zero

 

也可以用以下方式：

def fdiv1(x,y):    try:        return x/y    except (TypeError, ZeroDivisionError, Exception) as e:        print(e)


>>> fdiv1(‘ABC‘, 0)
unsupported operand type(s) for /: ‘str‘ and ‘int‘
>>> fdiv1(12,0)
division by zero

 

二、常用異常

‘---------------IOError:開啟檔案路徑出錯或不存在------------------‘try:    f = open(‘error.txt‘,‘r‘)except IOError as e:    print(‘開啟檔案出錯, 錯誤資訊：‘, e)‘--------------ImportError：匯入模組路徑出錯或不存在--------------‘try:    import errorexcept ImportError as e:    print(‘匯入模組出錯， 錯誤資訊：‘, e)‘--------------IndexError：索引出界----------------------------‘list1 = [1,2,3,4,5,6]try:    print(list1[6])except IndexError as e:    print(‘查詢列表出錯， 錯誤資訊：‘, e)‘----------------keyError：尋找字典中不存在的關鍵字---------------‘dict1 = {1:‘A‘, 2:‘B‘}try:    print(dict1[3])except KeyError as e:    print(‘查詢字典出錯， 錯誤資訊：‘, e)‘----------------TypeError：參數類型不符----------------------‘def fint(a):    print(a/2)try:    str1 = ‘ABC‘    fint(str1)except TypeError as e:    print(‘參數類型出錯， 錯誤資訊：‘, e)‘------------ValueError：參數類型匹配，但是傳入的值不對------------‘str1 = ‘ABC‘try:    print(int(str1))except ValueError as e:    print(‘參數值出錯， 錯誤資訊：‘, e)‘------------------NameError:使用的變數沒有賦值------------------‘try:    print(a)except NameError as e:    print(‘參數出錯， 錯誤資訊：‘, e)

 

三、自訂異常

class MyException(Exception):    def __init__(self, msg):        self.message = msg    def __str__(self):        return self.messagetry:    raise MyException(‘自訂異常‘)except MyException as e:    print(e)

 

四、主動拋出異常

try:    raise IOError(‘讀寫檔案出錯了‘)  #主動拋出IOError異常except IOError as e:    print(e)

 

五、try - except - else - finally

try:    f = open(‘test.txt‘, ‘r‘)except IOError as e:  #開啟檔案失敗，則拋出異常    print(e)else:                 #開啟檔案成功，則執行else塊    print(‘執行else‘)    f.close()finally:              #無論檔案是否正常開啟，都會執行finally塊    print(‘執行finally‘)

 

Python-異常處理