diff -r 5fea362b92fc Lib/xml/etree/ElementTree.py
--- a/Lib/xml/etree/ElementTree.py	Wed Apr 25 19:45:11 2012 +0200
+++ b/Lib/xml/etree/ElementTree.py	Fri Apr 27 23:41:08 2012 +0300
@@ -100,6 +100,7 @@
 import sys
 import re
 import warnings
+import io
 
 class _SimpleElementPath:
     # emulate pre-1.2 find/findtext/findall behaviour
@@ -834,17 +835,24 @@
         else:
             encoding = encoding.lower()
         if hasattr(file_or_filename, "write"):
-            file = file_or_filename
+            if encoding != "unicode":
+                file = io.TextIOWrapper(file_or_filename, encoding=encoding,
+                                        errors="xmlcharrefreplace",
+                                        write_through=True)
+            else:
+                file = file_or_filename
+            close_file = False
         else:
             if encoding != "unicode":
-                file = open(file_or_filename, "wb")
+                file = open(file_or_filename, "w", encoding=encoding,
+                            errors="xmlcharrefreplace")
             else:
                 file = open(file_or_filename, "w")
+            close_file = True
         if encoding != "unicode":
             def write(text):
                 try:
-                    return file.write(text.encode(encoding,
-                                                  "xmlcharrefreplace"))
+                    return file.write(text)
                 except (TypeError, AttributeError):
                     _raise_serialization_error(text)
         else:
@@ -864,8 +872,10 @@
             qnames, namespaces = _namespaces(self._root, default_namespace)
             serialize = _serialize[method]
             serialize(write, self._root, qnames, namespaces)
-        if file_or_filename is not file:
+        if close_file:
             file.close()
+        elif file_or_filename is not file:
+            file.detach()
 
     def write_c14n(self, file):
         # lxml.etree compatibility.  use output method instead
@@ -1159,11 +1169,10 @@
 # @defreturn string
 
 def tostring(element, encoding=None, method=None):
-    class dummy:
-        pass
     data = []
-    file = dummy()
+    file = io.BufferedIOBase()
     file.write = data.append
+    file.writable = lambda: True
     ElementTree(element).write(file, encoding, method=method)
     if encoding in (str, "unicode"):
         return "".join(data)
@@ -1186,11 +1195,10 @@
 # @since 1.3
 
 def tostringlist(element, encoding=None, method=None):
-    class dummy:
-        pass
     data = []
-    file = dummy()
+    file = io.BufferedIOBase()
     file.write = data.append
+    file.writable = lambda: True
     ElementTree(element).write(file, encoding, method=method)
     # FIXME: merge small fragments into larger parts
     return data