django1/django/core/paginator.py

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from copy import copy
from math import ceil
class InvalidPage(Exception):
pass
class ObjectPaginator:
"""
This class makes pagination easy. Feed it a module (an object with
get_count() and get_list() methods) and a dictionary of arguments
to be passed to those methods, plus the number of objects you want
on each page. Then read the hits and pages properties to see how
many pages it involves. Call get_page with a page number (starting
at 0) to get back a list of objects for that page.
Finally, check if a page number has a next/prev page using
has_next_page(page_number) and has_previous_page(page_number).
"""
def __init__(self, module, args, num_per_page, count_method='get_count', list_method='get_list'):
self.module, self.args = module, args
self.num_per_page = num_per_page
self.count_method, self.list_method = count_method, list_method
self._hits, self._pages = None, None
self._has_next = {} # Caches page_number -> has_next_boolean
def get_page(self, page_number):
try:
page_number = int(page_number)
except ValueError:
raise InvalidPage
if page_number < 0:
raise InvalidPage
args = copy(self.args)
args['offset'] = page_number * self.num_per_page
# Retrieve one extra record, and check for the existence of that extra
# record to determine whether there's a next page.
args['limit'] = self.num_per_page + 1
object_list = getattr(self.module, self.list_method)(**args)
if not object_list:
raise InvalidPage
self._has_next[page_number] = (len(object_list) > self.num_per_page)
return object_list[:self.num_per_page]
def has_next_page(self, page_number):
"Does page $page_number have a 'next' page?"
if not self._has_next.has_key(page_number):
if self._pages is None:
args = copy(self.args)
args['offset'] = (page_number + 1) * self.num_per_page
args['limit'] = 1
object_list = getattr(self.module, self.list_method)(**args)
self._has_next[page_number] = (object_list != [])
else:
self._has_next[page_number] = page_number < (self.pages - 1)
return self._has_next[page_number]
def has_previous_page(self, page_number):
return page_number > 0
def _get_hits(self):
if self._hits is None:
order_args = copy(self.args)
if order_args.has_key('order_by'):
del order_args['order_by']
if order_args.has_key('select_related'):
del order_args['select_related']
self._hits = getattr(self.module, self.count_method)(**order_args)
return self._hits
def _get_pages(self):
if self._pages is None:
self._pages = int(ceil(self.hits / float(self.num_per_page)))
return self._pages
hits = property(_get_hits)
pages = property(_get_pages)