def disposition_debug_msg(disp):
    """Make a nice debug message of what the FileDisposition is doing."""
    if disp.trace:
        msg = 'Tracing %r' % (disp.original_filename,)
        if disp.file_tracer:
            msg += ': will be traced by %r' % disp.file_tracer
    else:
        msg = 'Not tracing %r: %s' % (disp.original_filename, disp.reason)
    return msg
