def file_move_safe(old_file_name, new_file_name, chunk_size = 1024*64, allow_overwrite=False):
    """
    Moves a file from one location to another in the safest way possible.

    First, tries ``os.rename``, which is simple but will break across filesystems.
    If that fails, streams manually from one file to another in pure Python.

    If the destination file exists and ``allow_overwrite`` is ``False``, this
    function will throw an ``IOError``.
    """

    # There's no reason to move if we don't have to.
    if _samefile(old_file_name, new_file_name):
        return

    try:
        os.rename(old_file_name, new_file_name)
        return
    except __HOLE__:
        # This will happen with os.rename if moving to another filesystem
        # or when moving opened files on certain operating systems
        pass

    # first open the old file, so that it won't go away
    with open(old_file_name, 'rb') as old_file:
        # now open the new file, not forgetting allow_overwrite
        fd = os.open(new_file_name, os.O_WRONLY | os.O_CREAT | getattr(os, 'O_BINARY', 0) |
                                    (not allow_overwrite and os.O_EXCL or 0))
        try:
            locks.lock(fd, locks.LOCK_EX)
            current_chunk = None
            while current_chunk != b'':
                current_chunk = old_file.read(chunk_size)
                os.write(fd, current_chunk)
        finally:
            locks.unlock(fd)
            os.close(fd)
    copystat(old_file_name, new_file_name)

    try:
        os.remove(old_file_name)
    except OSError as e:
        # Certain operating systems (Cygwin and Windows) 
        # fail when deleting opened files, ignore it.  (For the 
        # systems where this happens, temporary files will be auto-deleted
        # on close anyway.)
        if getattr(e, 'winerror', 0) != 32 and getattr(e, 'errno', 0) != 13:
            raise
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.5/django/core/files/move.py/file_move_safe