为什么 Python 在调用 file.close() 后不释放文件句柄？

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).

Answer 3

Explained in the tutorial:

with open('/tmp/workfile', 'r') as f:
    read_data = f.read()

It works when you writing or pickling/unpickling, too

It's not really necessary that try finally block: Java way of doing things, not Python

Answer 4

I was looking for this, because the same thing happened to me. The question didn't help me, but I think I figured out what happened.

In the original version of the script I wrote, I neglected to add in a 'finally' clause to the file in case of an exception.

I was testing the script from the interactive prompt and got an exception while the file was open. What I didn't realize was that the file object wasn't immediately garbage-collected. After that, when I ran the script (still from the same interactive session), even though the new file objects were being closed, the first one still hadn't been, and so the file handle was still in use, from the perspective of the operating system.

Once I closed the interactive prompt, the problem went away, at which I remembered that exception occurring while the file was open and realized what had been going on. (Moral: Don't try to program on insufficient sleep. : ) )

Naturally, I have no idea if this is what happened in the case of the original poster, and even if the original poster is still around, they may not remember the specific circumstances, but the symptoms are similar, so I thought I'd add this as something to check for, for anyone caught in the same situation and looking for an answer.

Answer 5

I did it using intermediate file:

import os

f = open("report.tmp","w")
f.write("{}".format("Hello"))
f.close()
os.system("move report.tmp report.html") #this line is for Windows users