Slightly faster utf8 function

diff --git a/tornado/escape.py b/tornado/escape.py
index ee4ffb68c01acdf7a3b8bccd257d339aa1a2ba46..42c5ad76408c1d2e6f0f0ce6d9f8c8c2bb9b8402 100644 (file)
--- a/tornado/escape.py
+++ b/tornado/escape.py
@@ -92,13 +92,12 @@ def url_unescape(value):
     return _unicode(urllib.unquote_plus(value))
 
 
+_UTF8_TYPES = (bytes, type(None))
 def utf8(value):
-    if value is None:
-        return None
-    if isinstance(value, unicode):
-        return value.encode("utf-8")
-    assert isinstance(value, bytes)
-    return value
+    if isinstance(value, _UTF8_TYPES):
+        return value
+    assert isinstance(value, unicode)
+    return value.encode("utf-8")
 
 
 # I originally used the regex from