Python_try_except_finally

[python]
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x = 'abc'  
def fetcher(obj, index):  
    return obj[index]  
  
fetcher(x, 4)  

x = 'abc'
def fetcher(obj, index):
return obj[index]

fetcher(x, 4)

输出：

[plain]
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  File "test.py", line 6, in <module>  
    fetcher(x, 4)  
  File "test.py", line 4, in fetcher  
    return obj[index]  
IndexError: string index out of range  

File "test.py", line 6, in <module>
fetcher(x, 4)
File "test.py", line 4, in fetcher
return obj[index]
IndexError: string index out of range

第一： try不仅捕获异常，而且会恢复执行

[python]
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def catcher():  
    try:  
        fetcher(x, 4)  
    except:  
        print "got exception"  
    print "continuing"  

def catcher():
try:
fetcher(x, 4)
except:
print "got exception"
print "continuing"

输出：

[plain]
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got exception  
continuing  

got exception
continuing

第二：无论try是否发生异常，finally总会执行

[python]
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def catcher():  
    try:  
        fetcher(x, 4)  
    finally:  
        print 'after fecth'  

def catcher():
try:
fetcher(x, 4)
finally:
print 'after fecth'

输出：

[plain]
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after fecth  
Traceback (most recent call last):  
  File "test.py", line 55, in <module>  
    catcher()  
  File "test.py", line 12, in catcher  
    fetcher(x, 4)  
  File "test.py", line 4, in fetcher  
    return obj[index]  
IndexError: string index out of range  

after fecth
Traceback (most recent call last):
File "test.py", line 55, in <module>
catcher()
File "test.py", line 12, in catcher
fetcher(x, 4)
File "test.py", line 4, in fetcher
return obj[index]
IndexError: string index out of range

第三：try无异常，才会执行else

[python]
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def catcher():  
    try:  
        fetcher(x, 4)  
    except:  
        print "got exception"  
    else:  
        print "not exception"  

def catcher():
try:
fetcher(x, 4)
except:
print "got exception"
else:
print "not exception"

输出：

[plain]
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got exception  

got exception

[python]
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def catcher():  
    try:  
        fetcher(x, 2)  
    except:  
        print "got exception"  
    else:  
        print "not exception"  

def catcher():
try:
fetcher(x, 2)
except:
print "got exception"
else:
print "not exception"

输出：

[plain]
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not exception  

not exception

else作用：没有else语句，当执行完try语句后，无法知道是没有发生异常，还是发生了异常并被处理过了。通过else可以清楚的区分开。

第四：利用raise传递异常

[python]
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def catcher():  
    try:  
        fetcher(x, 4)  
    except:  
        print "got exception"  
        raise  

def catcher():
try:
fetcher(x, 4)
except:
print "got exception"
raise

输出：

[plain]
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got exception  
Traceback (most recent call last):  
  File "test.py", line 37, in <module>  
    catcher()  
  File "test.py", line 22, in catcher  
    fetcher(x, 4)  
  File "test.py", line 4, in fetcher  
    return obj[index]  
IndexError: string index out of range  

got exception
Traceback (most recent call last):
File "test.py", line 37, in <module>
catcher()
File "test.py", line 22, in catcher
fetcher(x, 4)
File "test.py", line 4, in fetcher
return obj[index]
IndexError: string index out of range

raise语句不包括异常名称或额外资料时，会重新引发当前异常。如果希望捕获处理一个异常，而又不希望
异常在程序代码中消失，可以通过raise重新引发该异常。

第五：except(name1, name2)

[python]
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def catcher():  
    try:  
        fetcher(x, 4)  
    except(TypeError, IndexError):  
        print "got exception"  
    else:  
        print "not exception"  

def catcher():
try:
fetcher(x, 4)
except(TypeError, IndexError):
print "got exception"
else:
print "not exception"

捕获列表列出的异常，进行处理。若except后无任何参数，则捕获所有异常。

[python]
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def catcher():  
    try:  
        fetcher(x, 4)  
    except:  
        print "got exception"  

def catcher():
try:
fetcher(x, 4)
except:
print "got exception"