addressing comments

Author: choldgraf

jupyter_sphinx/__init__.py

@@ -39,10 +39,16 @@
 def skip(self, node):
     raise docutils.nodes.SkipNode
 
+
 # Used for nodes that should be gone by rendering time (OutputMimeBundleNode)
 def halt(self, node):
-    raise ExtensionError((f"Rendering encountered a node type that should "
-                         "have been removed before rendering: {type(node)}"))
+    raise ExtensionError(
+        (
+            "Rendering encountered a node type that should "
+            "have been removed before rendering: %s" % type(node)
+        )
+    )
+
 
 # Renders the children of a container
 render_container = (

jupyter_sphinx/ast.py

@@ -442,22 +442,24 @@ def apply(self):
         # Image collect extra nodes from cell outputs that we need to process
         for node in self.document.traverse(image):
             # If the image node has `candidates` then it's already been processed
-            # as in-line markdown, so skip it
+            # as in-line content, so skip it
             if "candidates" in node:
                 continue
+            # re-initialize an ImageCollector because the `app` imagecollector instance
+            # is only available via event listeners.
             col = ImageCollector()
             col.process_doc(self.app, node)
 
 
 def _return_first_node_type(node, node_type):
     found_nodes = list(node.traverse(node_type))
     if len(found_nodes) == 0:
-        raise ValueError(f"Found no nodes of type {node_type} in node {node}")
+        raise ValueError("Found no nodes of type %s in node %s" % (node_type, node))
     if len(found_nodes) > 1:
         raise ValueError(
             (
-                f"Found more than one nodes of type {node_type} in node {node}. "
-                "only return the first instance"
+                "Found more than one nodes of type %s in node %s."
+                "only return the first instance" % (node_type, node)
             )
         )
     return found_nodes[0]