Imported Django from private SVN repository (created from r. 8825)

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/paginator.py

@@ -0,0 +1,76 @@
+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('ordering_tuple'):
+                del order_args['ordering_tuple']
+            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)