Cross-platform nearly ACID file updates

acid_write_file.py

import platform
import tempfile
import ntpath
import filelock  # https://github.com/dmfrey/FileLock

# It's interesting to see what's different between Windows and Linux.
# On Windows, you can't rename to an existing file, and you can't
# use os.fdatasync().
# Also see: http://blog.gocept.com/2013/07/15/reliable-file-updates-with-python/

def write_file(full_pathname, data):
    try:
        with filelock.FileLock(full_pathname):
            with tempfile.NamedTemporaryFile(mode='w', 
                    dir=ntpath.dirname(full_pathname), 
                    delete=False) as f:
                write_data_to_file(f, data)
                # exiting this "with" flushes, but does not sync
                f.flush()
                if platform.system() == "Windows":
                    os.fsync(f.fileno())  # Slower, but cross-platform
                    if os.path.exists(full_pathname):
                        os.unlink(full_pathname)  # otherwise WindowsError
                else:
                    os.fdatasync(f.fileno())  # Faster, Unix only
                tempname = f.name
            os.rename(tempname, full_pathname)  # Atomic on Unix, not Windows
    except filelock.FileLockException as e:
        do_something_with_exception(e)