How to safely open/close files in python 2.4

See docs.python.org:

When you’re done with a file, call f.close() to close it and free up any system resources taken up by the open file. After calling f.close(), attempts to use the file object will automatically fail.

Hence use close() elegantly with try/finally:

f = open('file.txt', 'r')

try:
    # do stuff with f
finally:
    f.close()

This ensures that even if # do stuff with f raises an exception, f will still be closed properly.

Note that open should appear outside of the try. If open itself raises an exception, the file wasn't opened and does not need to be closed. Also, if open raises an exception its result is not assigned to f and it is an error to call f.close().

In the above solution, repeated here:

f = open('file.txt', 'r')

try:
    # do stuff with f
finally:
   f.close()

if something bad happens (you never know ...) after opening the file successfully and before the try, the file will not be closed, so a safer solution is:

f = None
try:
    f = open('file.txt', 'r')

    # do stuff with f

finally:
    if f is not None:
       f.close()