'Restore the specified format from the previously saved
ORIGINAL_FORMAT, if any. Return True on success. The ORIGINAL_FORMAT is
deleted after a successful restore.'

@api
def restore_original_format(self, book_id, original_fmt):

    original_fmt = original_fmt.upper()
    fmtfile = self.format(book_id, original_fmt, as_file=True)
    if (fmtfile is not None):
        fmt = original_fmt.partition(u'_')[2]
        with fmtfile:
            self.add_format(book_id, fmt, fmtfile, run_hooks=False)
        self.remove_formats({book_id: (original_fmt,)})
        return True
    return False
