Why doesn't Python release file handles after calling file.close() ?

Question

I am on windows with Python 2.5. I have an open file for writing. I write some data. Call file close. When I try to delete the file from the folder using Windows Explorer, it errors, saying that a process still holds a handle to the file.

If I shutdown python, and try again, it succeeds.

Answer 1

It does close them. Are you sure f.close() is getting called? I just tested the same scenario and windows deletes the file for me.

Answer 2

Are you handling any exceptions around the file object? If so, make sure the error handling looks something like this:

f = open("hello.txt")
try:
    for line in f:
        print line
finally:
    f.close()

In considering why you should do this, consider the following lines of code:

f = open('hello.txt')
try:
    perform_an_operation_that_causes_f_to_raise_an_exception()
    f.close()
except IOError:
    pass

As you can see, f.close will never be called in the above code. The problem is that the above code will also cause f to not get garbage collected. The reason is that f will still be referenced in sys.traceback, in which case the only solution is to manually call close on f in a finally block or set sys.traceback to None (and I strongly recommend the former).