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from math import ceil
class InvalidPage(Exception):
pass
class ObjectPaginator(object):
"""
This class makes pagination easy. Feed it a QuerySet, 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, query_set, num_per_page):
self.query_set = query_set
self.num_per_page = num_per_page
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
# Retrieve one extra record, and check for the existence of that extra
# record to determine whether there's a next page.
limit = self.num_per_page + 1
offset = page_number * self.num_per_page
object_list = list(self.query_set[offset:offset+limit])
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:
offset = (page_number + 1) * self.num_per_page
self._has_next[page_number] = len(self.query_set[offset:offset+1]) > 0
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 first_on_page(self, page_number):
"""
Returns the 1-based index of the first object on the given page,
relative to total objects found (hits).
"""
if page_number == 0:
return 1
return (self.num_per_page * page_number) + 1
def last_on_page(self, page_number):
"""
Returns the 1-based index of the last object on the given page,
relative to total objects found (hits).
"""
if page_number == 0 and self.num_per_page >= self._hits:
return self._hits
elif page_number == (self._pages - 1) and (page_number + 1) * self.num_per_page > self._hits:
return self._hits
return (page_number + 1) * self.num_per_page
def _get_hits(self):
if self._hits is None:
self._hits = self.query_set.count()
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)
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