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                # try..finally 假如你在讀一個文件的時候,希望在無論異常發生與否的情況下都關閉文件,該怎么做呢?這可以使用`finally`塊來完成。注意,在一個`try`塊下,你可以同時使用`except`從句和`finally`塊。如果你要同時使用它們的話,需要把一個嵌入另外一個。 ``` #!/usr/bin/python # Filename: finally.py import time try: ????f = file('poem.txt') ????while True: # our usual file-reading idiom ????????line = f.readline() ????????if len(line) == 0: ????????????break ????????time.sleep(2) ????????print line, finally: ????f.close() ????print 'Cleaning up...closed the file' ``` (源文件:[code/finally.py](code/finally.py)) ## 輸出 ``` $ python finally.py Programming is fun When the work is done Cleaning up...closed the file Traceback (most recent call last): ??File "finally.py", line 12, in ? ????time.sleep(2) KeyboardInterrupt ``` ## 它如何工作 我們進行通常的讀文件工作,但是我有意在每打印一行之前用`time.sleep`方法暫停2秒鐘。這樣做的原因是讓程序運行得慢一些(Python由于其本質通常運行得很快)。在程序運行的時候,按**Ctrl-c**中斷/取消程序。 我們可以觀察到`KeyboardInterrupt`異常被觸發,程序退出。但是在程序退出之前,finally從句仍然被執行,把文件關閉
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