テンプレートで二重ループしたときのカウント方法

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カルーセルサンプルプログラム

<div class="row">
    <!--ここにカルーセルを入れてみる -->
    <div id="carouselControls" class="carousel slide" data-ride="carousel">
        <div class="carousel-inner">
            {% for category, books_record in book_records.items %}
                {% for book, acc, chapter, section in books_record %}
                    {% if forloop.parentloop.first %}
                        <div class="carousel-item active">
                            <img class="d-block w-50" alt="First slide" src="{{book.image.url}}">
                            <div class="carousel-caption d-none d-md-block">
                                <h5>{{book.title}}</h5>
                                <p>{{book.description | linebreaksbr}}</p>
                            </div>
                        </div>
                    {% else %}
                        <div class="carousel-item">
                            <img class="d-block w-50" alt="First slide" src="{{book.image.url}}">
                            <div class="carousel-caption d-none d-md-block">
                                <h5>{{book.title}}</h5>
                                <p>{{book.description | linebreaksbr}}</p>
                            </div>
                        </div>
                    {% endif %}
                {% endfor %}
            {% endfor %}
        </div>
        <a class="carousel-control-prev" href="#carouselControls" role="button" data-slide="prev">
            <span class="carousel-control-prev-icon" aria-hidden="true"></span>
            <span class="sr-only">前に戻る</span>
        </a>
        <a class="carousel-control-next" href="#carouselControls" role="button" data-slide="next">
            <span class="carousel-control-next-icon" aria-hidden="true"></span>
            <span class="sr-only">次に送る</span>
        </a>

    </div>
</div>