# Source code for django_tables2.paginators

    from django.core.paginator import EmptyPage, Page, PageNotAnInteger, Paginator
    from django.utils.translation import gettext as _

    class LazyPaginator(Paginator):
        """
        Implement lazy pagination, preventing any count() queries.

        By default, for any valid page, the total number of pages for the paginator will be

         - `current + 1` if the number of records fetched for the current page offset is
           bigger than the number of records per page.
         - `current` if the number of records fetched is less than the number of records per page.

        The number of additional records fetched can be adjusted using `look_ahead`, which
        defaults to 1 page. If you like to provide a little more extra information on how much
        pages follow the current page, you can use a higher value.

        .. note::

            The number of records fetched for each page is `per_page * look_ahead + 1`, so increasing
            the value for `look_ahead` makes the view a bit more expensive.

        So::

            paginator = LazyPaginator(range(10000), 10)

            >>> paginator.page(1).object_list
            [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
            >>> paginator.num_pages
            2
            >>> paginator.page(10).object_list
            [91, 92, 93, 94, 95, 96, 97, 98, 99, 100]
            >>> paginator.num_pages
            11
            >>> paginator.page(1000).object_list
            [9991, 9992, 9993, 9994, 9995, 9996, 9997, 9998, 9999]
            >>> paginator.num_pages
            1000

        Usage with `~.SingleTableView`::

            class UserListView(SingleTableView):
                table_class = UserTable
                table_data = User.objects.all()
                pagination_class = LazyPaginator

        Or with `~.RequestConfig`::

            RequestConfig(paginate={"paginator_class": LazyPaginator}).configure(table)

        .. versionadded :: 2.0.0
        """

        look_ahead = 1

        def __init__(self, object_list, per_page, look_ahead=None, **kwargs):
            self._num_pages = None
            self._final_num_pages = None
            if look_ahead is not None:
                self.look_ahead = look_ahead

            super().__init__(object_list, per_page, **kwargs)

        def validate_number(self, number):
            """Validate the given 1-based page number."""
            try:
                if isinstance(number, float) and not number.is_integer():
                    raise ValueError
                number = int(number)
            except (TypeError, ValueError):
                raise PageNotAnInteger(_("That page number is not an integer"))
            if number < 1:
                raise EmptyPage(_("That page number is less than 1"))
            return number

        def page(self, number):
            # Number might be None, because the total number of pages is not known in this paginator.
            # If an unknown page is requested, serve the first page.
            number = self.validate_number(number or 1)
            bottom = (number - 1) * self.per_page
            top = bottom + self.per_page
            # Retrieve more objects to check if there is a next page.
            look_ahead_items = (self.look_ahead - 1) * self.per_page + 1
            objects = list(self.object_list[bottom : top + self.orphans + look_ahead_items])
            objects_count = len(objects)
            if objects_count > (self.per_page + self.orphans):
                # If another page is found, increase the total number of pages.
                self._num_pages = number + (objects_count // self.per_page)
                # In any case,  return only objects for this page.
                objects = objects[: self.per_page]
            elif (number != 1) and (objects_count <= self.orphans):
                raise EmptyPage(_("That page contains no results"))
            else:
                # This is the last page.
                self._num_pages = number
                # For rendering purposes in `table_page_range`, we have to remember the final count
                self._final_num_pages = number
            return Page(objects, number, self)

        def is_last_page(self, number):
            return number == self._final_num_pages

        def _get_count(self):
            raise NotImplementedError

        count = property(_get_count)

        def _get_num_pages(self):
            return self._num_pages

        num_pages = property(_get_num_pages)

        def _get_page_range(self):
            raise NotImplementedError

        page_range = property(_get_page_range)