Python的異常處理

異常處理

目錄1.4對於捕獲異常的說明

例一

>>> i = input('請輸入數字')

請輸入數字：0
>>> print(i)
0>>> print(5 / int(i))
traceback (most recent call last):
file "", line 1, in zerodivisionerror: division by zero

例二

>>> i="qwe"

>>> print(5 / int(i))
traceback (most recent call last):
file "", line 1, in valueerror: invalid literal for int() with base 10: 'qwe'

python中的異常根類是baseexception，結構圖如下

baseexception

+-- systemexit
+-- keyboardinterrupt
+-- generatorexit
+-- exception
+-- stopiteration
+-- standarderror
| +-- buffererror
| +-- arithmeticerror
| | +-- floatingpointerror
| | +-- overflowerror
| | +-- zerodivisionerror
| +-- assertionerror
| +-- attributeerror
| +-- environmenterror
| | +-- ioerror
| | +-- oserror
| | +-- windowserror (windows)
| | +-- vmserror (vms)
| +-- eoferror
| +-- importerror
| +-- lookuperror
| | +-- indexerror
| | +-- keyerror
| +-- memoryerror
| +-- nameerror
| | +-- unboundlocalerror
| +-- referenceerror
| +-- runtimeerror
| | +-- notimplementederror
| +-- syntaxerror
| | +-- indentationerror
| | +-- taberror
| +-- systemerror
| +-- typeerror
| +-- valueerror
| +-- unicodeerror
| +-- unicodedecodeerror
| +-- unicodeencodeerror
| +-- unicodetranslateerror
+-- warning
+-- deprecationwarning
+-- pendingdeprecationwarning
+-- runtimewarning
+-- syntaxwarning
+-- userwarning
+-- futurewarning
+-- importwarning
+-- unicodewarning
+-- byteswarning

訪問不存在的成員

例如

>>> class animal(object):

pass
>>> a1 = animal()
>>> a1.run()
traceback (most recent call last):
file "", line 1, in a1.run()
attributeerror: 'animal' object has no attribute 'run'
>>> 
>>> print(a1.age)
traceback (most recent call last):
file "", line 1, in print(a1.age)
attributeerror: 'animal' object has no attribute 'age'

1.3.2 oserror 異常

oserror是作業系統相關異常，例如試圖開啟乙個不存在的檔案

>>> f=open("abc.txt")

traceback (most recent call last):
file "", line 1, in f=open("abc.txt")
filenotfounderror: [errno 2] no such file or directory: 'abc.txt'

是訪問元素時，下標超出索引最大值或最小值引發異常例如：

>>> code_list = [125, 56, 89, 36]

>>> code_list[4]
traceback (most recent call last):
file "", line 1, in code_list[4]
indexerror: list index out of range

是試圖訪問字典裡不存在的鍵引發，例如：

>>> dict1[104]

traceback (most recent call last):
file "", line 1, in dict1[104]
nameerror: name 'dict1' is not defined

1.3.5 nameerror 異常

nameerror是指試圖使用乙個不存在的變數引發的異常，pythonshell中執行例項

>>> value1

traceback (most recent call last):
file "", line 1, in nameerror: name 'value1' is not defined
>>> a = value1
traceback (most recent call last):
file "", line 1, in nameerror: name 'value1' is not defined
>>> value1 = 10
>>> value1
10

只有最後的value1 = 10，才讓value1有了值

1.3.6 typeerror 異常

typeerror是試圖傳入變數型別與要求的不符合時而引發的異常。pythonshell執行例項、

>>> i = '2'

>>> print(5 / i)
traceback (most recent call last):
file "", line 1, in print(5 / i)
typeerror: unsupported operand type(s) for /: 'int' and 'str'

1.3.7 valueerror 異常

valueerror是由於傳入乙個無效的引數值而引發的異常，這個異常在前面已經遇到了

>>> del i

>>> i = 'qwe'
>>> print( 5 / int(i))
traceback (most recent call last):
file "", line 1, in print( 5 / int(i))
valueerror: invalid literal for int() with base 10: 'qwe'

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