Limit feed node processing to Post nodes

Fixes #478.

instaloader/instaloader.py

@@ -703,8 +703,10 @@ class Instaloader:
 
         while True:
             feed = data["user"]["edge_web_feed_timeline"]
-            yield from (Post(self.context, edge["node"]) for edge in feed["edges"]
-                        if not edge["node"]["__typename"] == "GraphSuggestedUserFeedUnit")
+            for edge in feed["edges"]:
+                node = edge["node"]
+                if node.get("__typename") in Post.supported_graphql_types() and node.get("shortcode") is not None:
+                    yield Post(self.context, node)
             if not feed["page_info"]["has_next_page"]:
                 break
             data = self.context.graphql_query("d6f4427fbe92d846298cf93df0b937d3",

instaloader/structures.py

@@ -98,6 +98,11 @@ class Post:
             raise InvalidArgumentException("Wrong mediaid {0}, unable to convert to shortcode".format(str(mediaid)))
         return b64encode(mediaid.to_bytes(9, 'big'), b'-_').decode().replace('A', ' ').lstrip().replace(' ', 'A')
 
+    @staticmethod
+    def supported_graphql_types() -> List[str]:
+        """The values of __typename fields that the :class:`Post` class can handle."""
+        return ["GraphImage", "GraphVideo", "GraphSidecar"]
+
     def _asdict(self):
         node = self._node
         if self._full_metadata_dict: