support reverse iteration in PaginatedList

This uses the 'last' and 'prev' links in the HTTP headers.
The usage is repo.get_issues().reversed

github/PaginatedList.py

@@ -110,6 +110,20 @@ class PaginatedList(PaginatedListBase):
         self.__nextParams = firstParams or {}
         if self.__requester.per_page != 30:
             self.__nextParams["per_page"] = self.__requester.per_page
+        self._reversed = False
+
+    def _getLastPageUrl(self):
+        headers, data = self.__requester.requestJsonAndCheck("GET", self.__firstUrl, self.__nextParams, None)
+        links = self.__parseLinkHeader(headers)
+        lastUrl = links["last"]
+        return lastUrl
+
+    @property
+    def reversed(self):
+        self._reversed = True
+        self.__nextUrl = self._getLastPageUrl()
+        print "saved next url: %s" % self.__nextUrl
+        return self
 
     def _couldGrow(self):
         return self.__nextUrl is not None
@@ -118,21 +132,28 @@ class PaginatedList(PaginatedListBase):
         headers, data = self.__requester.requestJsonAndCheck("GET", self.__nextUrl, self.__nextParams, None)
 
         links = self.__parseLinkHeader(headers)
-        if len(data) > 0 and "next" in links:
-            self.__nextUrl = links["next"]
+        if len(data) > 0:
+            if self._reversed:
+                if "prev" in links:
+                    self.__nextUrl = links["prev"]
+            elif "next" in links:
+                self.__nextUrl = links["next"]
         else:
             self.__nextUrl = None
         self.__nextParams = None
 
-        return [
+        content = [
             self.__contentClass(self.__requester, element, completed=False)
             for element in data
         ]
+        if self._reversed:
+            return reversed(content)
+        return content
 
     def __parseLinkHeader(self, headers):
         links = {}
         if "link" in headers:
-            linkHeaders = headers["link"].split(",")
+            linkHeaders = headers["link"].split(", ")
             for linkHeader in linkHeaders:
                 (url, rel) = linkHeader.split("; ")
                 url = url[1:-1]

github/tests/PaginatedList.py

@@ -47,6 +47,19 @@ class PaginatedList(Framework.TestCase):
         self.assertEqual(self.list[0].id, 4772349)
         self.assertEqual(self.list[24].id, 4286936)
 
+    def testReversedIterationWithSinglePage(self):
+        r = self.list.reversed
+        self.assertEqual(r[0].id, 4286936)
+        self.assertEqual(r[1].id, 4317009)
+
+    def testReversedIterationWithMultiplePages(self):
+        r = self.list.reversed
+        self.assertEqual(r[0].id, 94898)
+        self.assertEqual(r[1].id, 104702)
+        self.assertEqual(r[13].id, 166211)
+        self.assertEqual(r[14].id, 166212)
+        self.assertEqual(r[15].id, 166214)
+
     def testIntIndexingInThirdPage(self):
         self.assertEqual(self.list[50].id, 3911629)
         self.assertEqual(self.list[74].id, 3605277)