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299 lines
9.2 KiB
Plaintext
299 lines
9.2 KiB
Plaintext
==========
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Pagination
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==========
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.. module:: django.core.paginator
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:synopsis: Classes to help you easily manage paginated data.
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Django provides a few classes that help you manage paginated data -- that is,
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data that's split across several pages, with "Previous/Next" links. These
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classes live in :file:`django/core/paginator.py`.
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Example
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=======
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Give :class:`Paginator` a list of objects, plus the number of items you'd like to
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have on each page, and it gives you methods for accessing the items for each
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page::
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>>> from django.core.paginator import Paginator
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>>> objects = ['john', 'paul', 'george', 'ringo']
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>>> p = Paginator(objects, 2)
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>>> p.count
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4
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>>> p.num_pages
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2
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>>> type(p.page_range)
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<class 'range_iterator'>
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>>> p.page_range
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range(1, 3)
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>>> page1 = p.page(1)
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>>> page1
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<Page 1 of 2>
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>>> page1.object_list
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['john', 'paul']
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>>> page2 = p.page(2)
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>>> page2.object_list
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['george', 'ringo']
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>>> page2.has_next()
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False
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>>> page2.has_previous()
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True
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>>> page2.has_other_pages()
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True
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>>> page2.next_page_number()
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Traceback (most recent call last):
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...
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EmptyPage: That page contains no results
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>>> page2.previous_page_number()
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1
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>>> page2.start_index() # The 1-based index of the first item on this page
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3
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>>> page2.end_index() # The 1-based index of the last item on this page
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4
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>>> p.page(0)
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Traceback (most recent call last):
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...
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EmptyPage: That page number is less than 1
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>>> p.page(3)
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Traceback (most recent call last):
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...
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EmptyPage: That page contains no results
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.. note::
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Note that you can give ``Paginator`` a list/tuple, a Django ``QuerySet``,
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or any other object with a ``count()`` or ``__len__()`` method. When
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determining the number of objects contained in the passed object,
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``Paginator`` will first try calling ``count()``, then fallback to using
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``len()`` if the passed object has no ``count()`` method. This allows
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objects such as Django's ``QuerySet`` to use a more efficient ``count()``
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method when available.
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Using ``Paginator`` in a view
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==============================
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Here's a slightly more complex example using :class:`Paginator` in a view to
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paginate a queryset. We give both the view and the accompanying template to
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show how you can display the results. This example assumes you have a
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``Contacts`` model that has already been imported.
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The view function looks like this::
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from django.core.paginator import Paginator, EmptyPage, PageNotAnInteger
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from django.shortcuts import render
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def listing(request):
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contact_list = Contacts.objects.all()
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paginator = Paginator(contact_list, 25) # Show 25 contacts per page
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page = request.GET.get('page')
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try:
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contacts = paginator.page(page)
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except PageNotAnInteger:
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# If page is not an integer, deliver first page.
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contacts = paginator.page(1)
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except EmptyPage:
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# If page is out of range (e.g. 9999), deliver last page of results.
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contacts = paginator.page(paginator.num_pages)
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return render(request, 'list.html', {'contacts': contacts})
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In the template :file:`list.html`, you'll want to include navigation between
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pages along with any interesting information from the objects themselves::
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{% for contact in contacts %}
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{# Each "contact" is a Contact model object. #}
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{{ contact.full_name|upper }}<br />
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...
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{% endfor %}
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<div class="pagination">
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<span class="step-links">
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{% if contacts.has_previous %}
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<a href="?page={{ contacts.previous_page_number }}">previous</a>
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{% endif %}
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<span class="current">
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Page {{ contacts.number }} of {{ contacts.paginator.num_pages }}.
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</span>
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{% if contacts.has_next %}
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<a href="?page={{ contacts.next_page_number }}">next</a>
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{% endif %}
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</span>
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</div>
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``Paginator`` objects
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=====================
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The :class:`Paginator` class has this constructor:
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.. class:: Paginator(object_list, per_page, orphans=0, allow_empty_first_page=True)
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Required arguments
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------------------
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``object_list``
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A list, tuple, ``QuerySet``, or other sliceable object with a ``count()``
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or ``__len__()`` method. For consistent pagination, ``QuerySet``\s should
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be ordered, e.g. with an :meth:`~django.db.models.query.QuerySet.order_by`
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clause or with a default :attr:`~django.db.models.Options.ordering` on the
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model.
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.. admonition:: Performance issues paginating large ``QuerySet``\s
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If you're using a ``QuerySet`` with a very large number of items,
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requesting high page numbers might be slow on some databases, because
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the resulting ``LIMIT``/``OFFSET`` query needs to count the number of
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``OFFSET`` records which takes longer as the page number gets higher.
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``per_page``
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The maximum number of items to include on a page, not including orphans
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(see the ``orphans`` optional argument below).
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Optional arguments
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------------------
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``orphans``
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Use this when you don't want to have a last page with very few items.
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If the last page would normally have a number of items less than or equal
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to ``orphans``, then those items will be added to the previous page (which
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becomes the last page) instead of leaving the items on a page by
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themselves. For example, with 23 items, ``per_page=10``, and
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``orphans=3``, there will be two pages; the first page with 10 items and
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the second (and last) page with 13 items. ``orphans`` defaults to zero,
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which means pages are never combined and the last page may have one item.
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``allow_empty_first_page``
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Whether or not the first page is allowed to be empty. If ``False`` and
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``object_list`` is empty, then an ``EmptyPage`` error will be raised.
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Methods
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-------
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.. method:: Paginator.page(number)
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Returns a :class:`Page` object with the given 1-based index. Raises
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:exc:`InvalidPage` if the given page number doesn't exist.
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Attributes
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----------
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.. attribute:: Paginator.count
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The total number of objects, across all pages.
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.. note::
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When determining the number of objects contained in ``object_list``,
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``Paginator`` will first try calling ``object_list.count()``. If
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``object_list`` has no ``count()`` method, then ``Paginator`` will
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fallback to using ``len(object_list)``. This allows objects, such as
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Django's ``QuerySet``, to use a more efficient ``count()`` method when
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available.
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.. attribute:: Paginator.num_pages
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The total number of pages.
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.. attribute:: Paginator.page_range
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A 1-based range iterator of page numbers, e.g. yielding ``[1, 2, 3, 4]``.
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``InvalidPage`` exceptions
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==========================
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.. exception:: InvalidPage
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A base class for exceptions raised when a paginator is passed an invalid
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page number.
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The :meth:`Paginator.page` method raises an exception if the requested page is
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invalid (i.e., not an integer) or contains no objects. Generally, it's enough
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to catch the ``InvalidPage`` exception, but if you'd like more granularity,
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you can catch either of the following exceptions:
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.. exception:: PageNotAnInteger
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Raised when ``page()`` is given a value that isn't an integer.
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.. exception:: EmptyPage
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Raised when ``page()`` is given a valid value but no objects exist on that
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page.
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Both of the exceptions are subclasses of :exc:`InvalidPage`, so you can handle
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them both with a simple ``except InvalidPage``.
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``Page`` objects
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================
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You usually won't construct ``Page`` objects by hand -- you'll get them
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using :meth:`Paginator.page`.
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.. class:: Page(object_list, number, paginator)
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A page acts like a sequence of :attr:`Page.object_list` when using
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``len()`` or iterating it directly.
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Methods
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-------
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.. method:: Page.has_next()
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Returns ``True`` if there's a next page.
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.. method:: Page.has_previous()
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Returns ``True`` if there's a previous page.
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.. method:: Page.has_other_pages()
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Returns ``True`` if there's a next *or* previous page.
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.. method:: Page.next_page_number()
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Returns the next page number. Raises :exc:`InvalidPage` if next page
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doesn't exist.
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.. method:: Page.previous_page_number()
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Returns the previous page number. Raises :exc:`InvalidPage` if previous
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page doesn't exist.
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.. method:: Page.start_index()
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Returns the 1-based index of the first object on the page, relative to all
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of the objects in the paginator's list. For example, when paginating a list
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of 5 objects with 2 objects per page, the second page's
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:meth:`~Page.start_index` would return ``3``.
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.. method:: Page.end_index()
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Returns the 1-based index of the last object on the page, relative to all
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of the objects in the paginator's list. For example, when paginating a list
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of 5 objects with 2 objects per page, the second page's
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:meth:`~Page.end_index` would return ``4``.
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Attributes
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----------
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.. attribute:: Page.object_list
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The list of objects on this page.
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.. attribute:: Page.number
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The 1-based page number for this page.
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.. attribute:: Page.paginator
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The associated :class:`Paginator` object.
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