python 教程 第十一章、 异常

第十一章、 异常
1)    try/except/else格式

try:
    s = raw_input('--> ')
except EOFError:
    print 'Why did you do an EOF on me?'
except:
    print 'Error occurred.'
else:
print 'Done' 

except参数说明:
except:             Catch all (or all other) exception types.
except name:         Catch a specific exception only.
except name as value:     Catch the listed exception and its instance.
except (name1, name2):     Catch any of the listed exceptions.
except (name1, name2) as value:  Catch any listed exception and its instance.
else:             Run if no exceptions are raised.
finally:             Always perform this block.

2)    try/finally格式

try:  
    fd=open("have-exists-file", "r")  
finally:  
fd.close() 

3)    try/except/else/finally通用格式

try:                        
    main-action
except Exception1:
    handler1
except Exception2:
    handler2
...
else:
    else-block
finally:
    finally-block 

4)    assert语句
用来声明某个条件是真的,并且在它非真的时候引发一个错误
assert len('abc') < 1

5)    raise引发异常

class ShortInputException(Exception):
    def __init__(self, length):
        Exception.__init__(self)
        self.length = length
try:
    s = raw_input('Enter something --> ')
    if len(s) < 3:
        raise ShortInputException(len(s))
except ShortInputException, x:
    print 'Exception: length %d ' % (x.length)
else:
print 'No exception.' 
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