try-finally

1. finally 關鍵字放在 try 後，中間可以有 except 及 else，不論有沒有異常發生，一定會執行 finally 區塊的程式碼。

   try:
   	You do your operations here;
   	......................
   except Exception:
   	If there is Exception, then execute this block.
   else:
   	If there is no exception then execute this block.
   finally:
   	This would always be executed.
   	......................
   

2. 範例：無論有無異常發生，最後一定列印「程式結束」。

   [dywang@dywmac zzz]$ cat except4.py 
   #!/usr/bin/python
   # coding: utf-8
   import sys
   
   try:
   	fo = open(sys.argv[1], "r")
   	data = fo.read()
   except IOError:
   	print "Error: can\'t read file", sys.argv[1]
   else:
   	wordlist = data.split()
   	print "Word count for", sys.argv[1], "=", len(wordlist)
   	fo.close()
   finally:
   	print "程式結束"
   

3. 執行結果：無論不存在的檔案 /etc/cde 或可讀取的檔案 /etc/resolv.conf，最後都印出「程式結束」。

   [dywang@dywmac zzz]$ ./except4.py /etc/cde
   Error: can't read file /etc/cde
   程式結束
   [dywang@dywmac zzz]$ ./except4.py /etc/resolv.conf 
   Word count for /etc/resolv.conf = 8
   程式結束