Flask SQLAlchemy Pagination without count query

pagination_without_count.py

def optimised_pagination(query, per_page, page):
    '''A more efficient pagination for SQLAlchemy
    Fetch one item before offset (to know if there's a previous page)
    Fetch one item after limit (to know if there's a next page)
    The trade-off is that the total items are not available, but if you don't need them
    there's no need for an extra COUNT query
    '''
    offset_start = (page - 1) * per_page

    query_offset = max(offset_start - 1, 0)
    optimistic_items = query.limit(per_page + 1).offset(query_offset).all()
    if page == 1:
        if len(optimistic_items) == per_page + 1:
            # On first page, there's no optimistic item for previous page
            items = optimistic_items[:-1]
        else:
            # The number of items on the first page is fewer than per_page
            items = optimistic_items
    elif len(optimistic_items) == per_page + 2:
        # We fetched an extra item on both ends
        items = optimistic_items[1:-1]
    else:
        # An extra item only on the head
        # This is the last page
        items = optimistic_items[1:]
    # This total is at least the number of items for the query, could be more
    total = offset_start + len(optimistic_items)
return Pagination(query, page, per_page, total, items)