What if you were reading a file and you wanted to close the file whether or not an
exception was raised? This can be done using the finally block.
Note that you can use an except clause along with a
finally block for the same corresponding try
block. You will have to embed one within another if you want to use both.
Example 13.3. Using Finally
#!/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'
$ 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
We do the usual file-reading stuff, but I've arbitrarily introduced a way
of sleeping for 2 seconds before printing each line using the
time.sleep method. The only reason is so that the
program runs slowly (Python is very fast by nature). When the program is
still running, press Ctrl-c
to interrupt/cancel the program.
Observe that a KeyboardInterrupt exception is thrown
and the program exits, but before the program exits, the finally clause is
executed and the file is closed.