diff -r d1e0931bc72e Lib/urllib.py
--- a/Lib/urllib.py	Fri Apr 30 15:47:34 2010 +0200
+++ b/Lib/urllib.py	Fri Apr 30 10:39:51 2010 -0400
@@ -27,6 +27,7 @@
 import os
 import time
 import sys
+import re
 from urlparse import urljoin as basejoin
 
 __all__ = ["urlopen", "URLopener", "FancyURLopener", "urlretrieve",
@@ -1184,6 +1185,15 @@
                '0123456789' '_.-')
 _safemaps = {}
 
+_faster_safe_test = always_safe + '/'
+_faster_safe = dict(zip(_faster_safe_test, _faster_safe_test))
+
+for c in [chr(i) for i in range(256)]:
+    if c not in _faster_safe:
+        _faster_safe[c] = '%%%02X' % ord(c)
+
+_must_quote = re.compile(r'[^%s]' % _faster_safe_test)
+
 def quote(s, safe = '/'):
     """quote('abc def') -> 'abc%20def'
 
@@ -1205,6 +1215,16 @@
     called on a path where the existing slash characters are used as
     reserved characters.
     """
+    # fastpath: empty (yes, Virginia, this acutally happens, a *lot*).
+    if not s:
+        return s
+    # fastpath: standard safechars, use regex to eliminate "clean" strings
+    # (again, this happens a *lot*).
+    if safe == '/':
+        if not _must_quote.search(s):
+            return s
+        return ''.join(map(_faster_safe.get, s))
+    # non-standard safechars 
     cachekey = (safe, always_safe)
     try:
         safe_map = _safemaps[cachekey]