diff -r 1704deb7e6d7 Lib/test/test_fileio.py
--- a/Lib/test/test_fileio.py	Sun Sep 16 00:13:10 2012 +0200
+++ b/Lib/test/test_fileio.py	Sat Sep 15 23:19:54 2012 -0300
@@ -10,6 +10,7 @@
 from functools import wraps
 
 from test.support import TESTFN, check_warnings, run_unittest, make_bad_fd
+from collections import UserList
 
 from _io import FileIO as _FileIO
 
@@ -68,6 +69,32 @@
         n = self.f.readinto(a)
         self.assertEqual(array('b', [1, 2]), a[:n])
 
+    def testWritelinesUserList(self):
+        # verify writeline with instance sequence
+        l = UserList([b'1', b'2'])
+        self.f.writelines(l)
+        self.f.close()
+        self.f = _FileIO(TESTFN, 'rb')
+        buf = self.f.read()
+        self.assertEqual(buf, b'12')
+
+    def testWritelinesIntegers(self):
+        # verify writelines with integers
+        self.assertRaises(TypeError, self.f.writelines, [1, 2, 3])
+
+    def testWritelinesIntegersUserList(self):
+        # verify writelines with integers in UserList
+        l = UserList([1,2,3])
+        self.assertRaises(TypeError, self.f.writelines, l)
+
+    def testWritelinesNonString(self):
+        # verify writelines with non-string object
+        class NonString:
+            pass
+
+        self.assertRaises(TypeError, self.f.writelines,
+                          [NonString(), NonString()])
+
     def test_none_args(self):
         self.f.write(b"hi\nbye\nabc")
         self.f.close()
diff -r 1704deb7e6d7 Lib/test/test_io.py
--- a/Lib/test/test_io.py	Sun Sep 16 00:13:10 2012 +0200
+++ b/Lib/test/test_io.py	Sat Sep 15 23:19:54 2012 -0300
@@ -32,7 +32,7 @@
 import unittest
 import warnings
 import weakref
-from collections import deque
+from collections import deque, UserList
 from itertools import cycle, count
 from test import support
 
@@ -407,6 +407,41 @@
         with self.open(support.TESTFN, "r") as f:
             self.assertRaises(TypeError, f.readline, 5.3)
 
+    def test_writelines(self):
+        with self.open(support.TESTFN, "wb", buffering=0) as f:
+            l = [b'a', b'b', b'c']
+            f.writelines(l)
+        with self.open(support.TESTFN, "rb") as f:
+            self.assertEqual(f.read(), b"abc")
+
+    def testWritelinesUserList(self):
+        # verify writelines with instance sequence
+        with self.open(support.TESTFN, "wb", buffering=0) as f:
+            l = UserList([b'1', b'2'])
+            f.writelines(l)
+        with self.open(support.TESTFN, "rb") as f:
+            self.assertEqual(f.read(), b"12")
+
+    def testWritelinesIntegers(self):
+        # verify writelines with integers
+        with self.open(support.TESTFN, "wb", buffering=0) as f:
+            self.assertRaises(TypeError, f.writelines, [1, 2, 3])
+
+    def testWritelinesIntegersUserList(self):
+        # verify writelines with integers in UserList
+        l = UserList([1,2,3])
+        with self.open(support.TESTFN, "wb", buffering=0) as f:
+            self.assertRaises(TypeError, f.writelines, l)
+
+    def testWritelinesNonString(self):
+        # verify writelines with non-string object
+        class NonString:
+            pass
+
+        with self.open(support.TESTFN, "wb", buffering=0) as f:
+            self.assertRaises(TypeError, f.writelines,
+                            [NonString(), NonString()])
+
     def test_raw_bytes_io(self):
         f = self.BytesIO()
         self.write_ops(f)
@@ -1193,6 +1228,46 @@
         bufio.flush()
         self.assertEqual(b"abc", writer._write_stack[0])
 
+    def testWritelines(self):
+        l = [b'a', b'b', b'c']
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        bufio.writelines(l)
+        bufio.flush()
+        self.assertEqual(b''.join(writer._write_stack), b'abc')
+
+    def testWritelinesUserList(self):
+        l = UserList([b'a', b'b', b'c'])
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        bufio.writelines(l)
+        bufio.flush()
+        self.assertEqual(b''.join(writer._write_stack), b'abc')
+
+    def testWritelinesIntegers(self):
+        # verify writelines with integers
+        l = [1, 2, 3]
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        self.assertRaises(TypeError, bufio.writelines, l)
+
+    def testWritelinesString(self):
+        # verify writelines with bytes
+        l = ['a', 'b', 'c']
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        self.assertRaises(TypeError, bufio.writelines, l)
+
+    def testWritelinesNonString(self):
+        # verify writelines with non-string object
+        class NonString:
+            pass
+
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        self.assertRaises(TypeError, bufio.writelines,
+                          [NonString(), NonString()])
+
     def test_destructor(self):
         writer = self.MockRawIO()
         bufio = self.tp(writer, 8)
@@ -1963,6 +2038,46 @@
         t.flush()
         self.assertEqual(b.getvalue(), b"abc?def\n")
 
+    def testWritelines(self):
+        lines = ['a', 'b', 'c']
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding='ascii')
+        t.writelines(lines)
+        t.flush()
+        self.assertEqual(b.getvalue(), b'abc')
+
+    def testWritelinesUserList(self):
+        lines = UserList(['a', 'b', 'c'])
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding='ascii')
+        t.writelines(lines)
+        t.flush()
+        self.assertEqual(b.getvalue(), b'abc')
+
+    def testWritelinesIntegers(self):
+        # verify writelines with integers
+        l = [1, 2, 3]
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding='ascii')
+        self.assertRaises(TypeError, t.writelines, l)
+
+    def testWritelinesBytes(self):
+        # verify writelines with bytes
+        l = [b'a', b'b', b'c']
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding='ascii')
+        self.assertRaises(TypeError, t.writelines, l)
+
+    def testWritelinesNonString(self):
+        # verify writelines with non-string object
+        class NonString:
+            pass
+
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding='ascii')
+        self.assertRaises(TypeError, t.writelines,
+                          [NonString(), NonString()])
+
     def test_newlines(self):
         input_lines = [ "unix\n", "windows\r\n", "os9\r", "last\n", "nonl" ]