It uses a temporary file in the same directory as the given path. This
ensures that the temporary file resides on the same filesystem.
The temporary file will then be atomically moved to the target
location: On POSIX, it will use rename if files should be overwritten,
otherwise a combination of link and unlink. On Windows, it uses
MoveFileEx through stdlib's ctypes with the appropriate flags.
Note that with link and unlink, there's a timewindow where the file
might be available under two entries in the filesystem: The name of
the temporary file, and the name of the target file.
Also note that the permissions of the target file may change this
way. In some situations a chmod can be issued without any concurrency
problems, but since that is not always the case, this library
doesn't do it by itself.
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