try-except-else

1. expect 語法：
   1. except: 不接任何異常屬性 exceptions，表示所有 exceptions 都符合。
   2. except Expection1: 接異常屬性 Exception1，表示符合 Exceptions1。
   3. except(Exception1[, Exception2[,...ExceptionN]]]): 接多個異常屬性，表示符合列出的 Exceptions1, Exceptions2, ...。
2. try - except - else 語法如下，當 try 執行後，符合 Exception 屬性，執行 expcet 區塊程式，其餘執行 else 區塊程式：

   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.
   

3. 範例：讀取命令指定的檔案，無法讀取時輸出Error: can't read file filename；成功讀取則列印檔案的字數。

   [dywang@dywmac zzz]$ cat except3.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()
   

4. 執行結果：/etc/abc 檔案不存在，無法讀取；/etc/issue 共有 11 個字。

   [dywang@dywmac zzz]$ ./except3.py /etc/abc
   Error: can't read file /etc/abc
   [dywang@dywmac zzz]$ ./except3.py /etc/issue
   Word count for /etc/issue = 11
   
   [dywang@dywmac zzz]$ cat /etc/issue
   De-Yu Wang Linux 6.4 release (Taiwan)
   Kernel \r on an \m