Update

Author: svekars

conf.py

@@ -158,6 +158,8 @@ def wrapper(*args, **kwargs):
     "author": "PyTorch Contributors",
 }
 
+
+
 # -- Sphinx-gallery configuration --------------------------------------------
 
 sphinx_gallery_conf = {
@@ -187,6 +189,11 @@ def wrapper(*args, **kwargs):
     },
 }
 
+html_additional_pages = {
+    "404": "404.html",
+}
+
+
 html_baseurl = "https://pytorch.org/tutorials/"  # needed for sphinx-sitemap
 sitemap_locales = [None]
 sitemap_excludes = [
@@ -259,6 +266,22 @@ def wrapper(*args, **kwargs):
         r"/(?!" + re.escape(os.getenv("GALLERY_PATTERN")) + r")[^/]+$"
     )
 
+# Add 404.html to each gallery directory and all subdirectories
+for i, gallery_dir in enumerate(sphinx_gallery_conf["gallery_dirs"]):
+    # Add 404.html to the main gallery directory
+    html_additional_pages[f"{gallery_dir}/404"] = "404.html"
+    
+    # Add 404.html to all subdirectories in the corresponding source directory
+    source_dir = Path(sphinx_gallery_conf["examples_dirs"][i])
+    if source_dir.exists():
+        # Find all subdirectories in the source directory
+        for subdir in source_dir.rglob("*"):
+            if subdir.is_dir() and subdir != source_dir:
+                # Calculate the relative path and corresponding gallery path
+                relative_path = subdir.relative_to(source_dir)
+                gallery_subdir = f"{gallery_dir}/{relative_path}"
+                html_additional_pages[f"{gallery_subdir}/404"] = "404.html"
+
 for i in range(len(sphinx_gallery_conf["examples_dirs"])):
     gallery_dir = Path(sphinx_gallery_conf["gallery_dirs"][i])
     source_dir = Path(sphinx_gallery_conf["examples_dirs"][i])