gh-151788: Speed up http.server directory listing by using os.scandir

mjbommar · claude · mjbommar · commit 0606d0283166 · 2026-06-20T09:00:37.000-04:00
SimpleHTTPRequestHandler.list_directory() called os.path.isdir() and
os.path.islink() for every entry, issuing two stat-family syscalls per
file. This is wasted work on any filesystem and dominates listing time
for large directories; on network filesystems such as NFS, where each
call is a round-trip, it becomes severe.

Use os.scandir(), whose DirEntry objects report the type from the
directory read itself (d_type / READDIRPLUS), eliminating the per-entry
stats in the common case and never doing more work than before.

Co-Authored-By: Claude Opus 4.8 (1M context) &lt;noreply@anthropic.com&gt;
diff --git a/Lib/http/server.py b/Lib/http/server.py
@@ -872,13 +872,13 @@ def list_directory(self, path):
 
         """
         try:
-            list = os.listdir(path)
+            with os.scandir(path) as it:
+                entries = sorted(it, key=lambda e: e.name.lower())
         except OSError:
             self.send_error(
                 HTTPStatus.NOT_FOUND,
                 "No permission to list directory")
             return None
-        list.sort(key=lambda a: a.lower())
         r = []
         displaypath = self.path
         displaypath = displaypath.split('#', 1)[0]
@@ -899,14 +899,16 @@ def list_directory(self, path):
         r.append(f'<title>{title}</title>\n</head>')
         r.append(f'<body>\n<h1>{title}</h1>')
         r.append('<hr>\n<ul>')
-        for name in list:
-            fullname = os.path.join(path, name)
+        for entry in entries:
+            name = entry.name
             displayname = linkname = name
-            # Append / for directories or @ for symbolic links
-            if os.path.isdir(fullname):
+            # Append / for directories or @ for symbolic links.
+            # Use cached os.DirEntry methods to avoid a stat() per entry,
+            # which is costly on network filesystems such as NFS.
+            if entry.is_dir():
                 displayname = name + "/"
                 linkname = name + "/"
-            if os.path.islink(fullname):
+            if entry.is_symlink():
                 displayname = name + "@"
                 # Note: a link to a directory displays with @ and links with /
             r.append('<li><a href="%s">%s</a></li>'
diff --git a/Misc/NEWS.d/next/Library/2026-06-20-09-00-26.gh-issue-151788.Gr8IxK.rst b/Misc/NEWS.d/next/Library/2026-06-20-09-00-26.gh-issue-151788.Gr8IxK.rst
@@ -0,0 +1,4 @@
+Speed up :class:`http.server.SimpleHTTPRequestHandler` directory listings by
+using :func:`os.scandir` instead of :func:`os.listdir` plus an :func:`os.stat`
+call per entry. This is faster on all filesystems and especially on network
+filesystems such as NFS.
