[tumblr] add option to sort photosets by upload order

gallery_dl/extractor/tumblr.py

@@ -63,6 +63,7 @@ class TumblrExtractor(Extractor):
         self.inline = self.config("inline", False)
         self.reblogs = self.config("reblogs", True)
         self.external = self.config("external", False)
+        self.sort_photos = self.config("sort", False)
 
         if len(self.types) == 1:
             self.api.posts_type = next(iter(self.types))
@@ -95,6 +96,9 @@ class TumblrExtractor(Extractor):
                 photos = post["photos"]
                 del post["photos"]
 
+                if self.sort_photos and len(photos) > 1:
+                    photos.sort(key=self._get_tumblr_offset)
+
                 for photo in photos:
                     post["photo"] = photo
                     photo.update(photo["original_size"])
@@ -161,6 +165,15 @@ class TumblrExtractor(Extractor):
 
         return Message.Urllist, _original_image(url), post
 
+    @staticmethod
+    def _get_tumblr_offset(photo):
+        """Return the offset embedded in a photo's URL"""
+        return util.safe_int(
+            photo["original_size"]["url"]
+            .rpartition("_")[0]
+            .rpartition("o")[2]
+        )
+
 
 class TumblrUserExtractor(TumblrExtractor):
     """Extractor for all images from a tumblr-user"""