python try except finally raise

稍微总结一下，否则总是忘。

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

 fetcher(x, 4)

输出：

   File "test.py", line 6, in
     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

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

输出：

 got exception
 continuing

第二：无论try是否发生异常，finally总会执行

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

输出：

 after fecth
 Traceback (most recent call last):
   File "test.py", line 55, in
     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

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

输出：

 got exception

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

输出：

 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

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

输出：

 got exception
 Traceback (most recent call last):
   File "test.py", line 37, in
     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)

 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。

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