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class InvalidPage(Exception):
pass
class ObjectPaginator(object):
"""
This class makes pagination easy. Feed it a QuerySet or list, 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).
Use orphans to avoid small final pages. For example:
13 records, num_per_page=10, orphans=2 --> pages==2, len(self.get_page(0))==10
12 records, num_per_page=10, orphans=2 --> pages==1, len(self.get_page(0))==12
"""
def __init__(self, query_set, num_per_page, orphans=0):
self.query_set = query_set
self.num_per_page = num_per_page
self.orphans = orphans
self._hits = self._pages = None
def validate_page_number(self, page_number):
try:
page_number = int(page_number)
except ValueError:
raise InvalidPage
if page_number < 0 or page_number > self.pages - 1:
raise InvalidPage
return page_number
def get_page(self, page_number):
page_number = self.validate_page_number(page_number)
bottom = page_number * self.num_per_page
top = bottom + self.num_per_page
if top + self.orphans >= self.hits:
top = self.hits
return self.query_set[bottom:top]
def has_next_page(self, page_number):
"Does page $page_number have a 'next' page?"
return page_number < self.pages - 1
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).
"""
page_number = self.validate_page_number(page_number)
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).
"""
page_number = self.validate_page_number(page_number)
page_number += 1 # 1-base
if page_number == self.pages:
return self.hits
return page_number * self.num_per_page
def _get_hits(self):
if self._hits is None:
# Try .count() or fall back to len().
try:
self._hits = int(self.query_set.count())
except (AttributeError, TypeError, ValueError):
# AttributeError if query_set has no object count.
# TypeError if query_set.count() required arguments.
# ValueError if int() fails.
self._hits = len(self.query_set)
return self._hits
def _get_pages(self):
if self._pages is None:
hits = (self.hits - 1 - self.orphans)
if hits < 1:
hits = 0
self._pages = hits // self.num_per_page + 1
return self._pages
hits = property(_get_hits)
pages = property(_get_pages)
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