Python Exception handling

The purpose of exception handling is to prevent the user from seeing unfriendly exceptions and to avoid the program exiting unexpectedly.

I. Through try...except ... Intercept the exception to ensure that the program continues execution

Try:open (' Test.txt ', ' R ') 1/0except zerodivisionerror,e:print eprint ' done '

Run the above program directly throws an exception as follows, the statement after the 2nd line is not executed, the program exits directly

>>>

Traceback (most recent):

File "D:\Python\code\test.py", line 2, <module>

Open (' Test.txt ', ' R ')

IOError: [Errno 2] No such file or directory: ' Test.txt '

>>>

Next we'll run the two-line statement swap position of the try

try:1/0 open (' Test.txt ', ' R ') except Zerodivisionerror,e:print eprint ' done '

>>>

Integer division or modulo by zero

Done

>>>

You can see that done is printed and the exception is intercepted, ensuring that the program continues to execute

Two. Finally clause: Execute with or without exception, commonly used for file close, release operation of database connection

Try:1/1except zerodivisionerror,e:print efinally:print ' done '

>>>

Done

>>>

Program no exception still print out done

Three. Exception throws raise clause: actively throws an exception to the previous layer for API error handling, masking the underlying exception, etc.

Try:1/0except exception,e:print str (e) Raise Exception (' Test raise ')

>>>

Integer division or modulo by zero

Traceback (most recent):

File "D:\Python\code\test.py", line 5, <module>

Raise Exception (' Test raise ')

Exception:test Raise

>>>

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Python Exception handling