Try... Except exception handling statement (6)

Catalog

1. abnormal

2. exception handling

2.1 try...except

2.2 try...except...else

2.3 try...except...finally

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While the program is running , We often encounter all kinds of mistakes , These mistakes are collectively called “ abnormal ”.

1. abnormal

Common anomalies and descriptions

abnormal	describe
SyntaxError:invalid syntax	invalid syntax
NameError	An error caused by an attempt to access an undeclared variable
IndexError	The index is out of range of the sequence, causing an error
IndentationError	The indentation error
ValueError	The value passed in is wrong
KeyError	Requesting a nonexistent dictionary keyword caused an error
IOError	I / O error
ImportError	When import Statement cannot find the error caused by the module
AttributeError	Error raised when trying to access unknown object properties
TypeError	Errors caused by improper type
MemoryError	Out of memory
ZeroDivisionError	When the divisor is 0 Error caused by

2. exception handling

2.1 try...except

When use , Put the code that may cause the exception in try In the block , Put the result of the treatment on except In the block , such , once try An error occurred in the code in the statement block , Will execute except Code in statement block ; But if try There are no errors in the code in the statement block , Will not perform except Code in statement block .

The syntax is as follows ：

try:
    block1
except[ExceptionName[as alias]]:
    block2
#block1: Represents a block of code that may have errors 
#ExceptionName[as alias]: Optional parameters , Used to specify the exception to catch .ExceptionName Indicates the name of the exception to catch ,as alias The alias that records the specific content of the exception .
#block2: Code block for exception handling 

for example ：

Before processing ：

def division(a,b):
    result = a/b
    print(result)

division(4,2)
division(4,0)

The operation results are as follows ：

2.0
Traceback (most recent call last):
  File "E:\PYTHON\base4.py", line 25, in <module>
    division(4,0)
  File "E:\PYTHON\base4.py", line 21, in division
    result = a/b
ZeroDivisionError: division by zero

There is no exception after processing ：

def division(a,b):
    result = a/b
    print(result)

if __name__ == '__main__':# Regulations , The main program , The following code is executed by default 
    try:
        division(4,2)
        print(' succeed , Divisor normal ')
    except ZeroDivisionError:
        print(' Something went wrong , The divisor cannot be zero 0')

The operation results are as follows ：

2.0
 succeed , Divisor normal 

Catch exception after processing ：

def division(a,b):
    result = a/b
    print(result)

if __name__ == '__main__':# Regulations , The main program , The following code is executed by default 
    try:
        division(4,0)
        print(' succeed , Divisor normal ')
    except ZeroDivisionError:
        print(' Something went wrong , The divisor cannot be zero 0')

The operation results are as follows ：

 Something went wrong , The divisor cannot be zero 0

2.2 try...except...else

try...except...else sentence ,else Statement is used to specify when try Statement block to execute when no exception is found in statement block .

for example ：

def division(a,b):
    result = a/b
    print(result)

if __name__ == '__main__':# Regulations , The main program , The following code is executed by default 
    try:
        division(4,2)
    except ZeroDivisionError:
        print(' Something went wrong , The divisor cannot be zero 0')
    else:
        print(' succeed , Divisor normal , Deo gratias ！')

The operation results are as follows ：

2.0
 succeed , Divisor normal , Deo gratias ！

2.3 try...except...finally

If there is some code in the program that must be executed in any case , Then you can put it in finally In the code block of the statement .

for example ：

def division(a,b):
    result = a/b
    print(result)

if __name__ == '__main__':# Regulations , The main program , The following code is executed by default 
    try:
        division(4,2)
    except ZeroDivisionError:
        print(' Something went wrong , The divisor cannot be zero 0')
    else:
        print(' succeed , Divisor normal , Deo gratias ！')
    finally:
        print('over')

The operation results are as follows ：

2.0
 succeed , Divisor normal , Deo gratias ！
over