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.'