Steven D'Aprano wrote:
<cut>
import os, fcntl
oldname = "ham.txt"
newname = "spam.txt"
def lock_destination(name):
fileno = os.open(name, os.O_CREAT | os.O_EXCL)
fcntl.flock(fileno, fcntl.LOCK_EX) # POSIX systems only
return fileno
# Create a test file to be renamed.
f = open(oldname, 'w')
f.write('this is my file\n')
f.close()
fileno = lock_destination(newname)
# At this point, I can see "ham.txt" plus an empty file
# "spam.txt" in my file browser
os.rename(oldname, newname)
The rename works, but here is my problem: after getting what I thought
was an exclusive lock on the new file, but before calling os.rename(), I
can still over-write it from another process:
$ echo "this comes from another process" > spam.txt
$ cat spam.txt
this comes from another process
<cut>
This is weird, you would indeed expect it to be locked, I tried it on
FreeBSD and it behaves the same.
I guess the behavior of os.rename should be changed so it raises an
exception when the source destination exists independent on the below
platform.
I tried searching for another way to do it but the closest I came was to
popen mv and raise an exception if it asks to overwrite the existing file.
Sorry I can't be of more help.
--
mph
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