def _add_new_user(user_rec_sys_data, product_category, review_score):
    """
    Adds new user rating to the user_rec_sys_data.

    Parameters
    ----------
        user_rec_sys_data: Reviews data for adding new user.
        product_category: Product Selected on the website.
        review_score: Rating given for the item.

    Yields
    ------
        Updates user_rec_sys_data.csv

    Returns
    -------
        updated_data, new_user_id.
    """

    # Computing new_user_id.
    new_user_raw_id = user_rec_sys_data["customer_id"].max() + 1
    new_data = {"customer_id": new_user_raw_id,
                "product_category": product_category,
                "review_score": review_score}

    updated_data = user_rec_sys_data.append(new_data, ignore_index=True)
    return updated_data, new_user_raw_id