diff -r e0f997a7aaa5 Lib/test/test_xml_etree.py
--- a/Lib/test/test_xml_etree.py	Sun May 20 18:34:11 2012 +0200
+++ b/Lib/test/test_xml_etree.py	Mon May 21 01:26:35 2012 +0300
@@ -923,6 +923,10 @@
     b'<tag>abc</tag>'
     >>> serialize(elem, encoding="iso-8859-1")
     b"<?xml version='1.0' encoding='iso-8859-1'?>\n<tag>abc</tag>"
+    >>> serialize(elem, encoding="utf-16").decode('utf-16')
+    "<?xml version='1.0' encoding='utf-16'?>\n<tag>abc</tag>"
+    >>> serialize(elem, encoding="utf-32").decode('utf-32')
+    "<?xml version='1.0' encoding='utf-32'?>\n<tag>abc</tag>"
 
     >>> elem.text = "<&\"\'>"
     >>> serialize(elem)
@@ -933,6 +937,10 @@
     b'<tag>&lt;&amp;"\'&gt;</tag>'
     >>> serialize(elem, encoding="iso-8859-1")
     b'<?xml version=\'1.0\' encoding=\'iso-8859-1\'?>\n<tag>&lt;&amp;"\'&gt;</tag>'
+    >>> serialize(elem, encoding="utf-16").decode('utf-16')
+    '<?xml version=\'1.0\' encoding=\'utf-16\'?>\n<tag>&lt;&amp;"\'&gt;</tag>'
+    >>> serialize(elem, encoding="utf-32").decode('utf-32')
+    '<?xml version=\'1.0\' encoding=\'utf-32\'?>\n<tag>&lt;&amp;"\'&gt;</tag>'
 
     >>> elem.attrib["key"] = "<&\"\'>"
     >>> elem.text = None
@@ -944,6 +952,10 @@
     b'<tag key="&lt;&amp;&quot;\'&gt;" />'
     >>> serialize(elem, encoding="iso-8859-1")
     b'<?xml version=\'1.0\' encoding=\'iso-8859-1\'?>\n<tag key="&lt;&amp;&quot;\'&gt;" />'
+    >>> serialize(elem, encoding="utf-16").decode('utf-16')
+    '<?xml version=\'1.0\' encoding=\'utf-16\'?>\n<tag key="&lt;&amp;&quot;\'&gt;" />'
+    >>> serialize(elem, encoding="utf-32").decode('utf-32')
+    '<?xml version=\'1.0\' encoding=\'utf-32\'?>\n<tag key="&lt;&amp;&quot;\'&gt;" />'
 
     >>> elem.text = '\xe5\xf6\xf6<>'
     >>> elem.attrib.clear()
@@ -955,6 +967,10 @@
     b'<tag>&#229;&#246;&#246;&lt;&gt;</tag>'
     >>> serialize(elem, encoding="iso-8859-1")
     b"<?xml version='1.0' encoding='iso-8859-1'?>\n<tag>\xe5\xf6\xf6&lt;&gt;</tag>"
+    >>> serialize(elem, encoding="utf-16").decode('utf-16')
+    "<?xml version='1.0' encoding='utf-16'?>\n<tag>åöö&lt;&gt;</tag>"
+    >>> serialize(elem, encoding="utf-32").decode('utf-32')
+    "<?xml version='1.0' encoding='utf-32'?>\n<tag>åöö&lt;&gt;</tag>"
 
     >>> elem.attrib["key"] = '\xe5\xf6\xf6<>'
     >>> elem.text = None
@@ -966,6 +982,10 @@
     b'<tag key="&#229;&#246;&#246;&lt;&gt;" />'
     >>> serialize(elem, encoding="iso-8859-1")
     b'<?xml version=\'1.0\' encoding=\'iso-8859-1\'?>\n<tag key="\xe5\xf6\xf6&lt;&gt;" />'
+    >>> serialize(elem, encoding="utf-16").decode('utf-16')
+    '<?xml version=\'1.0\' encoding=\'utf-16\'?>\n<tag key="åöö&lt;&gt;" />'
+    >>> serialize(elem, encoding="utf-32").decode('utf-32')
+    '<?xml version=\'1.0\' encoding=\'utf-32\'?>\n<tag key="åöö&lt;&gt;" />'
     """
 
 def methods():
@@ -2081,6 +2101,27 @@
         self.assertEqual(tree.getroot().tag, 'site')
 
 
+class UserIOTest(unittest.TestCase):
+    class dummy:
+        pass
+
+    def test_read_from_user_reader(self):
+        raw = io.BytesIO(b'''<?xml version="1.0"?><site></site>''')
+        reader = self.dummy()
+        reader.read = raw.read
+        tree = ET.ElementTree()
+        tree.parse(reader)
+        self.assertEqual(tree.getroot().tag, 'site')
+
+    def test_write_to_user_writer(self):
+        raw = io.BytesIO()
+        writer = self.dummy()
+        writer.write = raw.write
+        tree = ET.parse(io.BytesIO(b'''<site />'''))
+        tree.write(writer)
+        self.assertEqual(raw.getvalue(), b'''<site />''')
+
+
 class ParseErrorTest(unittest.TestCase):
     def test_subclass(self):
         self.assertIsInstance(ET.ParseError(), SyntaxError)
@@ -2155,6 +2196,7 @@
         ElementSlicingTest,
         BasicElementTest,
         StringIOTest,
+        UserIOTest,
         ParseErrorTest,
         ElementTreeTest,
         TreeBuilderTest]
diff -r e0f997a7aaa5 Lib/xml/etree/ElementTree.py
--- a/Lib/xml/etree/ElementTree.py	Sun May 20 18:34:11 2012 +0200
+++ b/Lib/xml/etree/ElementTree.py	Mon May 21 01:26:35 2012 +0300
@@ -100,6 +100,7 @@
 import sys
 import re
 import warnings
+import io
 
 class _SimpleElementPath:
     # emulate pre-1.2 find/findtext/findall behaviour
@@ -835,20 +836,29 @@
             encoding = encoding.lower()
         if hasattr(file_or_filename, "write"):
             file = file_or_filename
+            if encoding != "unicode":
+                if not isinstance(file, io.BufferedIOBase):
+                    file = io.BufferedIOBase()
+                    file.writable = lambda: True
+                    file.write = file_or_filename.write
+                    try:
+                        # Required to write BOM
+                        file.seekable = file_or_filename.seekable
+                        file.tell = file_or_filename.tell
+                    except AttributeError:
+                        pass
+                file = io.TextIOWrapper(file, encoding=encoding,
+                                        errors="xmlcharrefreplace",
+                                        newline="\n")
+            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")
-        if encoding != "unicode":
-            def write(text):
-                try:
-                    return file.write(text.encode(encoding,
-                                                  "xmlcharrefreplace"))
-                except (TypeError, AttributeError):
-                    _raise_serialization_error(text)
-        else:
-            write = file.write
+            close_file = True
+        write = file.write
         if method == "xml" and (xml_declaration or
                 (xml_declaration is None and
                  encoding not in ("utf-8", "us-ascii", "unicode"))):
@@ -864,8 +874,10 @@
             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
@@ -1159,10 +1171,9 @@
 # @defreturn string
 
 def tostring(element, encoding=None, method=None):
-    class dummy:
-        pass
     data = []
-    file = dummy()
+    file = io.BufferedIOBase()
+    file.writable = lambda: True
     file.write = data.append
     ElementTree(element).write(file, encoding, method=method)
     if encoding in (str, "unicode"):
@@ -1186,10 +1197,9 @@
 # @since 1.3
 
 def tostringlist(element, encoding=None, method=None):
-    class dummy:
-        pass
     data = []
-    file = dummy()
+    file = io.BufferedIOBase()
+    file.writable = lambda: True
     file.write = data.append
     ElementTree(element).write(file, encoding, method=method)
     # FIXME: merge small fragments into larger parts