Can anyone explain this weird behaviour of shutil.rmtree and shutil.copytree?

Question

I'm building a relatively simple application that asks for directories, checks if they're correct, and then removes one of them and recreates it with contents of the other one. I'm encountering this weird behaviour, I'll try to explain:

When I've got the destination folder window open, AND it's empty, there's an access denied exception, then I get kicked out of the folder and it gets removed. But then if it's not empty, it works just fine, no exceptions, the destination directory (from what it seems) gets emptied then filled with files from the source directory. Which is strange because it's supposed to straight out remove the destination folder no matter what, and then recreate it with the same name and contents from the source destination.

This doesn't make sense to me, shouldn't there be the exact same exception when I'm browsing the directory when it's not empty as when it's empty? What's the difference, it's still supposed to just delete the folder. Is there any logical explanation to that? Also, if there's an exception, why does the directory get removed anyway?

Code for this particular part is pretty straightforward (please keep in mind I'm a beginner :) )

def Delete(self, dest):

    try:
        shutil.rmtree(dest)
        self.Paste(self.src, dest)
    except (IOError, os.error) as e:
        print e

def Paste(self, src, dest):

    try:
        shutil.copytree(src, dest)
    except (IOError, os.error) as e:
        print e

Answer 1

This is expected behaviour on Windows.

Internally shutil.rmtree calls the windows API function DeleteFile which is documented on MSDN (http://msdn.microsoft.com/en-us/library/windows/desktop/aa363915%28v=vs.85%29.aspx).

This function has the following property (highlite by me):

The DeleteFile function marks a file for deletion on close. Therefore, the file deletion does not occur until the last handle to the file is closed. Subsequent calls to CreateFile to open the file fail with ERROR_ACCESS_DENIED.

If any other process still has a handle open (e.g. virus scanners, windows explorer because you watch the directory or anything else that might still have a handle to that directory), it will not go away.

Usually you just catch the exception in your Paste operation and retry it a few times/for some dozend milliseconds, to handle all those weird virus scanner anomalies.

Little bonus: You can use windbg or ProcessExplorer to find out who still keeps an open handle to your file (just use Find Handle in Process explorer and search for the filename).