def cut_off_str(obj, max_len):
    """ Creates a string representation of an object, no longer than max_len characters
        
        Uses repr(obj) to create the string representation. If this is longer than max_len -3 
        characters, the last three will be replaced with elipsis.
    """
    s = repr(obj)
    if len(s) > max_len - 3:
        s = s[:max_len - 3] + '...'
    return s