def dict_sub(attrs1, attrs2):
    """Remove attributes `attrs2` from `attrs1`."""
    new_dict = {}
    for key in attrs1:
        if key in attrs2:
            new_set = attrs1[key].difference(attrs2[key])
            if new_set:
                new_dict[key] = new_set
        else:
            new_dict[key] = attrs1[key]
    return new_dict