python—day24

Exception handling:

1. What is an exception:

　　An exception is a signal that an error has occurred,

　　Once the program fails, if there is no corresponding processing mechanism in the program

　　Then the error will generate an exception and throw it

　　The running of the program is also terminated

2. An exception is divided into three parts:

　　1. Abnormal tracking information;

　　2. The type of exception;

　　3. Abnormal value;

3, abnormal classification

　　1. Syntax exception:

1  Such exceptions should be corrected before program execution
 2          print ( ' start.... ' )
 3          x=1
 4          x+=1
 5          if 
6          print ( ' stop.... ' )
 7  IndexError
 8 l=[ ' a ' , ' b ' ]
 9 l[100 ]
 10  
11  KeyError
 12 d={ ' a ' :1 }
 13 d[ ' b ' ]
14 
15 AttributeError:
16 class Foo:
17     pass
18 
19 Foo.x
20 import os
21 os.aaa
22 
23 
24 ZeroDivisionError
25 1 / 0
26 
27 
28 FileNotFoundError
29 f=open('a.txt','r',encoding='utf-8')
30 
31 ValueError: I/O operation on closed file.
32 f=open('a.txt','r',encoding='utf-8')
33 f.close()
34 f.readline()
35 
36 ValueError: invalid literal for int() with base 10: 'aaaaa'
37 int('aaaaa')
38 
39 
40 TypeError
41 for i in 333:
42     pass
43 
44 NameError
45 x
46 func()

View Code

　　2. Logical exception:

1  single branch:
 2  try :
 3      print ( ' start... ' )
 4      x = 1
 5      y
 6      l = []
 7      l[3 ]
 8      d = { ' a ' : 1 }
 9      d[ ' b ' ]
 10      print ( ' end... ' )
 11  
12  except NameError:
 13      print ( ' The variable name is not defined ')
14

try-out
 : print
     ( ' start ... ' )
    x = 1
    and
    l = []
    l[3]
    d = {'a': 1}
    d['b']
    print('end...')

except NameError:
     print ( ' The variable name is not defined ' )
 except KeyError:
     print ( ' The key of the dictionary does not exist ' )
 except IndexError:
     print ( ' The index is out of the range of the list ' )

print('other...')

1  Multiple exceptions are handled by the same piece of logic
 2  try :
 3      print ( ' start... ' )
 4      x = 1
 5      y
 6      l = []
 7      l[3 ]
 8      d = { ' a ' : 1 }
 9      d [ ' b ' ]
 10      print ( ' end... ' )
 11  
12  except (NameError,KeyError,IndexError):
 13      print ( 'There is a problem with the variable name or the key of the dictionary or the index of the list! ' )
 14  
15  print ( ' other... ' )

1  universal exception
 2  try :
 3      print ( ' start... ' )
 4      x = 1
 5      y
 6      l = []
 7      l[3 ]
 8      d = { ' a ' : 1 }
 9      d[ ' b ' ]
 10      print ( ' end... ' )
 11  except Exception as e:
 12      print ( ' universal exception ' ,e)

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