nts:
    'prefix', 'suffix', 'dir' -- as for mkstemp.
    'mode' -- the mode argument to io.open (default "w+b").
    'buffering' -- the buffer size argument to io.open (default -1).
    'encoding' -- the encoding argument to io.open (default None)
    'newline' -- the newline argument to io.open (default None)
    'delete' -- whether the file is deleted on close (default True).
    'errors' -- the errors argument to io.open (default None)
    The file is created as mkstemp() would do it.

    Returns an object with a file-like interface; the name of the file
    is accessible as its 'name' attribute.  The file will be automatically
    deleted when it is closed unless the 'delete' argument is set to False.
    rh