diff --git a/Doc/tools/indfix.py b/Doc/tools/indfix.py
index 5bab0fb..23f9e17 100755
--- a/Doc/tools/indfix.py
+++ b/Doc/tools/indfix.py
@@ -19,7 +19,7 @@
 __version__ = '$Revision$'
 
 import re
-import StringIO
+import io
 import sys
 
 
@@ -50,7 +50,7 @@
         ifp = open(ifn)
     if ofn is None:
         ofn = ifn
-    ofp = StringIO.StringIO()
+    ofp = io.StringIO()
     entries = []
     match = breakable_re.match
     write = ofp.write
diff --git a/Doc/tools/sgmlconv/docfixer.py b/Doc/tools/sgmlconv/docfixer.py
index 9f93966..8459fa2 100755
--- a/Doc/tools/sgmlconv/docfixer.py
+++ b/Doc/tools/sgmlconv/docfixer.py
@@ -1055,8 +1055,8 @@
         ofp = sys.stdout
     elif len(sys.argv) == 3:
         ifp = open(sys.argv[1])
-        import StringIO
-        ofp = StringIO.StringIO()
+        import io
+        ofp = io.StringIO()
     else:
         usage()
         sys.exit(2)
diff --git a/Lib/StringIO.py b/Lib/StringIO.py
deleted file mode 100644
index 815bce6..0000000
--- a/Lib/StringIO.py
+++ /dev/null
@@ -1,324 +0,0 @@
-r"""File-like objects that read from or write to a string buffer.
-
-This implements (nearly) all stdio methods.
-
-f = StringIO()      # ready for writing
-f = StringIO(buf)   # ready for reading
-f.close()           # explicitly release resources held
-flag = f.isatty()   # always false
-pos = f.tell()      # get current position
-f.seek(pos)         # set current position
-f.seek(pos, mode)   # mode 0: absolute; 1: relative; 2: relative to EOF
-buf = f.read()      # read until EOF
-buf = f.read(n)     # read up to n bytes
-buf = f.readline()  # read until end of line ('\n') or EOF
-list = f.readlines()# list of f.readline() results until EOF
-f.truncate([size])  # truncate file at to at most size (default: current pos)
-f.write(buf)        # write at current position
-f.writelines(list)  # for line in list: f.write(line)
-f.getvalue()        # return whole file's contents as a string
-
-Notes:
-- Using a real file is often faster (but less convenient).
-- There's also a much faster implementation in C, called cStringIO, but
-  it's not subclassable.
-- fileno() is left unimplemented so that code which uses it triggers
-  an exception early.
-- Seeking far beyond EOF and then writing will insert real null
-  bytes that occupy space in the buffer.
-- There's a simple test set (see end of this file).
-"""
-try:
-    from errno import EINVAL
-except ImportError:
-    EINVAL = 22
-
-__all__ = ["StringIO"]
-
-def _complain_ifclosed(closed):
-    if closed:
-        raise ValueError, "I/O operation on closed file"
-
-class StringIO:
-    """class StringIO([buffer])
-
-    When a StringIO object is created, it can be initialized to an existing
-    string by passing the string to the constructor. If no string is given,
-    the StringIO will start empty.
-
-    The StringIO object can accept either Unicode or 8-bit strings, but
-    mixing the two may take some care. If both are used, 8-bit strings that
-    cannot be interpreted as 7-bit ASCII (that use the 8th bit) will cause
-    a UnicodeError to be raised when getvalue() is called.
-    """
-    def __init__(self, buf = ''):
-        # Force self.buf to be a string or unicode
-        if not isinstance(buf, basestring):
-            buf = str(buf)
-        self.buf = buf
-        self.len = len(buf)
-        self.buflist = []
-        self.pos = 0
-        self.closed = False
-
-    def __iter__(self):
-        return self
-
-    def __next__(self):
-        """A file object is its own iterator, for example iter(f) returns f
-        (unless f is closed). When a file is used as an iterator, typically
-        in a for loop (for example, for line in f: print line), the __next__()
-        method is called repeatedly. This method returns the next input line,
-        or raises StopIteration when EOF is hit.
-        """
-        _complain_ifclosed(self.closed)
-        r = self.readline()
-        if not r:
-            raise StopIteration
-        return r
-
-    def close(self):
-        """Free the memory buffer.
-        """
-        if not self.closed:
-            self.closed = True
-            del self.buf, self.pos
-
-    def isatty(self):
-        """Returns False because StringIO objects are not connected to a
-        tty-like device.
-        """
-        _complain_ifclosed(self.closed)
-        return False
-
-    def seek(self, pos, mode = 0):
-        """Set the file's current position.
-
-        The mode argument is optional and defaults to 0 (absolute file
-        positioning); other values are 1 (seek relative to the current
-        position) and 2 (seek relative to the file's end).
-
-        There is no return value.
-        """
-        _complain_ifclosed(self.closed)
-        if self.buflist:
-            self.buf += ''.join(self.buflist)
-            self.buflist = []
-        if mode == 1:
-            pos += self.pos
-        elif mode == 2:
-            pos += self.len
-        self.pos = max(0, pos)
-
-    def tell(self):
-        """Return the file's current position."""
-        _complain_ifclosed(self.closed)
-        return self.pos
-
-    def read(self, n=None):
-        """Read at most size bytes from the file
-        (less if the read hits EOF before obtaining size bytes).
-
-        If the size argument is negative or omitted, read all data until EOF
-        is reached. The bytes are returned as a string object. An empty
-        string is returned when EOF is encountered immediately.
-        """
-        _complain_ifclosed(self.closed)
-        if self.buflist:
-            self.buf += ''.join(self.buflist)
-            self.buflist = []
-        if n is None:
-            n = -1
-        if n < 0:
-            newpos = self.len
-        else:
-            newpos = min(self.pos+n, self.len)
-        r = self.buf[self.pos:newpos]
-        self.pos = newpos
-        return r
-
-    def readline(self, length=None):
-        r"""Read one entire line from the file.
-
-        A trailing newline character is kept in the string (but may be absent
-        when a file ends with an incomplete line). If the size argument is
-        present and non-negative, it is a maximum byte count (including the
-        trailing newline) and an incomplete line may be returned.
-
-        An empty string is returned only when EOF is encountered immediately.
-
-        Note: Unlike stdio's fgets(), the returned string contains null
-        characters ('\0') if they occurred in the input.
-        """
-        _complain_ifclosed(self.closed)
-        if self.buflist:
-            self.buf += ''.join(self.buflist)
-            self.buflist = []
-        i = self.buf.find('\n', self.pos)
-        if i < 0:
-            newpos = self.len
-        else:
-            newpos = i+1
-        if length is not None:
-            if self.pos + length < newpos:
-                newpos = self.pos + length
-        r = self.buf[self.pos:newpos]
-        self.pos = newpos
-        return r
-
-    def readlines(self, sizehint = 0):
-        """Read until EOF using readline() and return a list containing the
-        lines thus read.
-
-        If the optional sizehint argument is present, instead of reading up
-        to EOF, whole lines totalling approximately sizehint bytes (or more
-        to accommodate a final whole line).
-        """
-        total = 0
-        lines = []
-        line = self.readline()
-        while line:
-            lines.append(line)
-            total += len(line)
-            if 0 < sizehint <= total:
-                break
-            line = self.readline()
-        return lines
-
-    def truncate(self, size=None):
-        """Truncate the file's size.
-
-        If the optional size argument is present, the file is truncated to
-        (at most) that size. The size defaults to the current position.
-        The current file position is not changed unless the position
-        is beyond the new file size.
-
-        If the specified size exceeds the file's current size, the
-        file remains unchanged.
-        """
-        _complain_ifclosed(self.closed)
-        if size is None:
-            size = self.pos
-        elif size < 0:
-            raise IOError(EINVAL, "Negative size not allowed")
-        elif size < self.pos:
-            self.pos = size
-        self.buf = self.getvalue()[:size]
-        self.len = size
-
-    def write(self, s):
-        """Write a string to the file.
-
-        There is no return value.
-        """
-        _complain_ifclosed(self.closed)
-        if not s: return
-        # Force s to be a string or unicode
-        if not isinstance(s, basestring):
-            s = str(s)
-        spos = self.pos
-        slen = self.len
-        if spos == slen:
-            self.buflist.append(s)
-            self.len = self.pos = spos + len(s)
-            return
-        if spos > slen:
-            self.buflist.append('\0'*(spos - slen))
-            slen = spos
-        newpos = spos + len(s)
-        if spos < slen:
-            if self.buflist:
-                self.buf += ''.join(self.buflist)
-            self.buflist = [self.buf[:spos], s, self.buf[newpos:]]
-            self.buf = ''
-            if newpos > slen:
-                slen = newpos
-        else:
-            self.buflist.append(s)
-            slen = newpos
-        self.len = slen
-        self.pos = newpos
-
-    def writelines(self, iterable):
-        """Write a sequence of strings to the file. The sequence can be any
-        iterable object producing strings, typically a list of strings. There
-        is no return value.
-
-        (The name is intended to match readlines(); writelines() does not add
-        line separators.)
-        """
-        write = self.write
-        for line in iterable:
-            write(line)
-
-    def flush(self):
-        """Flush the internal buffer
-        """
-        _complain_ifclosed(self.closed)
-
-    def getvalue(self):
-        """
-        Retrieve the entire contents of the "file" at any time before
-        the StringIO object's close() method is called.
-
-        The StringIO object can accept either Unicode or 8-bit strings,
-        but mixing the two may take some care. If both are used, 8-bit
-        strings that cannot be interpreted as 7-bit ASCII (that use the
-        8th bit) will cause a UnicodeError to be raised when getvalue()
-        is called.
-        """
-        if self.buflist:
-            self.buf += ''.join(self.buflist)
-            self.buflist = []
-        return self.buf
-
-
-# A little test suite
-
-def test():
-    import sys
-    if sys.argv[1:]:
-        file = sys.argv[1]
-    else:
-        file = '/etc/passwd'
-    lines = open(file, 'r').readlines()
-    text = open(file, 'r').read()
-    f = StringIO()
-    for line in lines[:-2]:
-        f.write(line)
-    f.writelines(lines[-2:])
-    if f.getvalue() != text:
-        raise RuntimeError, 'write failed'
-    length = f.tell()
-    print('File length =', length)
-    f.seek(len(lines[0]))
-    f.write(lines[1])
-    f.seek(0)
-    print('First line =', repr(f.readline()))
-    print('Position =', f.tell())
-    line = f.readline()
-    print('Second line =', repr(line))
-    f.seek(-len(line), 1)
-    line2 = f.read(len(line))
-    if line != line2:
-        raise RuntimeError, 'bad result after seek back'
-    f.seek(len(line2), 1)
-    list = f.readlines()
-    line = list[-1]
-    f.seek(f.tell() - len(line))
-    line2 = f.read()
-    if line != line2:
-        raise RuntimeError, 'bad result after seek back from EOF'
-    print('Read', len(list), 'more lines')
-    print('File length =', f.tell())
-    if f.tell() != length:
-        raise RuntimeError, 'bad length'
-    f.truncate(length/2)
-    f.seek(0, 2)
-    print('Truncated length =', f.tell())
-    if f.tell() != length/2:
-        raise RuntimeError, 'truncate did not adjust length'
-    f.close()
-
-if __name__ == '__main__':
-    test()
diff --git a/Lib/bsddb/test/test_compare.py b/Lib/bsddb/test/test_compare.py
index b3eaf3a..522ff57 100644
--- a/Lib/bsddb/test/test_compare.py
+++ b/Lib/bsddb/test/test_compare.py
@@ -3,7 +3,7 @@
 """
 
 import sys, os, re
-from cStringIO import StringIO
+from io import StringIO
 
 from . import test_all
 
diff --git a/Lib/cookielib.py b/Lib/cookielib.py
index 313912e..3a716d2 100644
--- a/Lib/cookielib.py
+++ b/Lib/cookielib.py
@@ -58,7 +58,7 @@
     # catching input that's bad in unexpected ways.  Warn if any
     # exceptions are caught there.
     import warnings, traceback, StringIO
-    f = StringIO.StringIO()
+    f = io.StringIO()
     traceback.print_exc(None, f)
     msg = f.getvalue()
     warnings.warn("cookielib bug!\n%s" % msg, stacklevel=2)
diff --git a/Lib/ctypes/test/test_random_things.py b/Lib/ctypes/test/test_random_things.py
index 2f8e667..e803895 100644
--- a/Lib/ctypes/test/test_random_things.py
+++ b/Lib/ctypes/test/test_random_things.py
@@ -37,9 +37,9 @@
 
     def capture_stderr(self, func, *args, **kw):
         # helper - call function 'func', and return the captured stderr
-        import StringIO
+        import io
         old_stderr = sys.stderr
-        logger = sys.stderr = StringIO.StringIO()
+        logger = sys.stderr = io.StringIO()
         try:
             func(*args, **kw)
         finally:
diff --git a/Lib/distutils/command/register.py b/Lib/distutils/command/register.py
index 10a903e..91081dd 100644
--- a/Lib/distutils/command/register.py
+++ b/Lib/distutils/command/register.py
@@ -8,7 +8,7 @@
 __revision__ = "$Id$"
 
 import sys, os, urllib2, getpass, urlparse
-import StringIO, ConfigParser
+import io, ConfigParser
 
 from distutils.core import Command
 from distutils.errors import *
@@ -253,7 +253,7 @@
         boundary = '--------------GHSKFJDLGDS7543FJKLFHRE75642756743254'
         sep_boundary = '\n--' + boundary
         end_boundary = sep_boundary + '--'
-        body = StringIO.StringIO()
+        body = io.StringIO()
         for key, value in data.items():
             # handle multiple entries for the same name
             if type(value) not in (type([]), type( () )):
diff --git a/Lib/distutils/command/upload.py b/Lib/distutils/command/upload.py
index d1cf87a..1ca2fb9 100644
--- a/Lib/distutils/command/upload.py
+++ b/Lib/distutils/command/upload.py
@@ -14,7 +14,6 @@
 import httplib
 import base64
 import urlparse
-import cStringIO as StringIO
 
 class upload(Command):
 
@@ -135,7 +134,7 @@
         boundary = '--------------GHSKFJDLGDS7543FJKLFHRE75642756743254'
         sep_boundary = '\n--' + boundary
         end_boundary = sep_boundary + '--'
-        body = StringIO.StringIO()
+        body = io.StringIO()
         for key, value in data.items():
             # handle multiple entries for the same name
             if type(value) != type([]):
diff --git a/Lib/distutils/tests/test_build_py.py b/Lib/distutils/tests/test_build_py.py
index 54a4ed8..75b6624 100644
--- a/Lib/distutils/tests/test_build_py.py
+++ b/Lib/distutils/tests/test_build_py.py
@@ -2,7 +2,7 @@
 
 import os
 import sys
-import StringIO
+import io
 import unittest
 
 from distutils.command.build_py import build_py
@@ -69,7 +69,7 @@
         open(os.path.join(testdir, "testfile"), "w").close()
 
         os.chdir(sources)
-        sys.stdout = StringIO.StringIO()
+        sys.stdout = io.StringIO()
 
         try:
             dist = Distribution({"packages": ["pkg"],
diff --git a/Lib/distutils/tests/test_dist.py b/Lib/distutils/tests/test_dist.py
index 8d4b070..23506b5 100644
--- a/Lib/distutils/tests/test_dist.py
+++ b/Lib/distutils/tests/test_dist.py
@@ -4,7 +4,7 @@
 import distutils.dist
 import os
 import shutil
-import StringIO
+import io
 import sys
 import tempfile
 import unittest
@@ -177,7 +177,7 @@
                            "obsoletes": ["my.pkg (splat)"]})
 
     def format_metadata(self, dist):
-        sio = StringIO.StringIO()
+        sio = io.StringIO()
         dist.metadata.write_pkg_file(sio)
         return sio.getvalue()
 
diff --git a/Lib/doctest.py b/Lib/doctest.py
index bc30a1a..0f40818 100644
--- a/Lib/doctest.py
+++ b/Lib/doctest.py
@@ -98,7 +98,7 @@
 import sys, traceback, inspect, linecache, os, re
 import unittest, difflib, pdb, tempfile
 import warnings
-from StringIO import StringIO
+from io import StringIO
 
 # There are 4 basic classes:
 #  - Example: a <source, want> pair, plus an intra-docstring line number.
diff --git a/Lib/email/generator.py b/Lib/email/generator.py
index c480229..fb03c9f 100644
--- a/Lib/email/generator.py
+++ b/Lib/email/generator.py
@@ -12,7 +12,7 @@
 import random
 import warnings
 
-from cStringIO import StringIO
+from io import StringIO
 from email.header import Header
 
 UNDERSCORE = '_'
diff --git a/Lib/email/iterators.py b/Lib/email/iterators.py
index 155e19e..e4476e3 100644
--- a/Lib/email/iterators.py
+++ b/Lib/email/iterators.py
@@ -12,7 +12,7 @@
     ]
 
 import sys
-from cStringIO import StringIO
+from io import StringIO
 
 
 
diff --git a/Lib/email/message.py b/Lib/email/message.py
index 1767bfb..78e7d82 100644
--- a/Lib/email/message.py
+++ b/Lib/email/message.py
@@ -10,7 +10,7 @@
 import uu
 import binascii
 import warnings
-from cStringIO import StringIO
+from io import StringIO
 
 # Intrapackage imports
 import email.charset
diff --git a/Lib/email/mime/audio.py b/Lib/email/mime/audio.py
index c7290c4..f40bcbd 100644
--- a/Lib/email/mime/audio.py
+++ b/Lib/email/mime/audio.py
@@ -8,7 +8,7 @@
 
 import sndhdr
 
-from cStringIO import StringIO
+from io import StringIO
 from email import encoders
 from email.mime.nonmultipart import MIMENonMultipart
 
diff --git a/Lib/email/parser.py b/Lib/email/parser.py
index 2fcaf25..782b985 100644
--- a/Lib/email/parser.py
+++ b/Lib/email/parser.py
@@ -7,7 +7,7 @@
 __all__ = ['Parser', 'HeaderParser']
 
 import warnings
-from cStringIO import StringIO
+from io import StringIO
 
 from email.feedparser import FeedParser
 from email.message import Message
diff --git a/Lib/email/test/test_email.py b/Lib/email/test/test_email.py
index c7c61ef..5e8d652 100644
--- a/Lib/email/test/test_email.py
+++ b/Lib/email/test/test_email.py
@@ -9,7 +9,7 @@
 import difflib
 import unittest
 import warnings
-from cStringIO import StringIO
+from io import StringIO
 
 import email
 
diff --git a/Lib/email/test/test_email_renamed.py b/Lib/email/test/test_email_renamed.py
index 4688a1b..ea5b1a1 100644
--- a/Lib/email/test/test_email_renamed.py
+++ b/Lib/email/test/test_email_renamed.py
@@ -9,7 +9,7 @@
 import difflib
 import unittest
 import warnings
-from cStringIO import StringIO
+from io import StringIO
 
 import email
 
diff --git a/Lib/email/test/test_email_torture.py b/Lib/email/test/test_email_torture.py
index d708b74..67f106a 100644
--- a/Lib/email/test/test_email_torture.py
+++ b/Lib/email/test/test_email_torture.py
@@ -9,7 +9,7 @@
 import sys
 import os
 import unittest
-from cStringIO import StringIO
+from io import StringIO
 from types import ListType
 
 from email.test.test_email import TestEmailBase
diff --git a/Lib/email/utils.py b/Lib/email/utils.py
index de9fbf8..ce4b313 100644
--- a/Lib/email/utils.py
+++ b/Lib/email/utils.py
@@ -27,7 +27,7 @@
 import socket
 import urllib
 import warnings
-from cStringIO import StringIO
+from io import StringIO
 
 from email._parseaddr import quote
 from email._parseaddr import AddressList as _AddressList
diff --git a/Lib/io.py b/Lib/io.py
index 43695be..1ee465a 100644
--- a/Lib/io.py
+++ b/Lib/io.py
@@ -303,6 +303,8 @@
 
         Returns False if we don't know.
         """
+        if self.closed:
+            raise ValueError("isatty() on closed file")
         return False
 
     ### Readline[s] and writelines ###
@@ -1239,8 +1241,11 @@
                                        encoding=encoding,
                                        newline=newline)
         if initial_value:
+            if not isinstance(initial_value, basestring):
+                initial_value = str(initial_value)
             self.write(initial_value)
             self.seek(0)
 
     def getvalue(self):
+        self.flush()
         return self.buffer.getvalue().decode(self._encoding)
diff --git a/Lib/logging/__init__.py b/Lib/logging/__init__.py
index 2c1e706..229be69 100644
--- a/Lib/logging/__init__.py
+++ b/Lib/logging/__init__.py
@@ -26,7 +26,7 @@
 To use, simply 'import logging' and log away!
 """
 
-import sys, os, time, cStringIO, traceback
+import sys, os, time, io, traceback
 
 try:
     import codecs
@@ -396,7 +396,7 @@
         This default implementation just uses
         traceback.print_exception()
         """
-        sio = cStringIO.StringIO()
+        sio = io.StringIO()
         traceback.print_exception(ei[0], ei[1], ei[2], None, sio)
         s = sio.getvalue()
         sio.close()
diff --git a/Lib/mailbox.py b/Lib/mailbox.py
index 2a6b24c..79feae0 100755
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -19,7 +19,7 @@
 import email.message
 import email.generator
 import rfc822
-import StringIO
+import io
 try:
     if sys.platform == 'os2emx':
         # OS/2 EMX fcntl() not adequate
@@ -194,7 +194,7 @@
         # used in strings and by email.Message are translated here.
         """Dump message contents to target file."""
         if isinstance(message, email.message.Message):
-            buffer = StringIO.StringIO()
+            buffer = io.StringIO()
             gen = email.generator.Generator(buffer, mangle_from_, 0)
             gen.flatten(message)
             buffer.seek(0)
@@ -1141,13 +1141,13 @@
         start, stop = self._lookup(key)
         self._file.seek(start)
         self._file.readline()   # Skip '1,' line specifying labels.
-        original_headers = StringIO.StringIO()
+        original_headers = io.StringIO()
         while True:
             line = self._file.readline()
             if line == '*** EOOH ***' + os.linesep or not line:
                 break
             original_headers.write(line.replace(os.linesep, '\n'))
-        visible_headers = StringIO.StringIO()
+        visible_headers = io.StringIO()
         while True:
             line = self._file.readline()
             if line == os.linesep or not line:
@@ -1166,7 +1166,7 @@
         start, stop = self._lookup(key)
         self._file.seek(start)
         self._file.readline()   # Skip '1,' line specifying labels.
-        original_headers = StringIO.StringIO()
+        original_headers = io.StringIO()
         while True:
             line = self._file.readline()
             if line == '*** EOOH ***' + os.linesep or not line:
@@ -1182,7 +1182,7 @@
 
     def get_file(self, key):
         """Return a file-like representation or raise a KeyError."""
-        return StringIO.StringIO(self.get_string(key).replace('\n',
+        return io.StringIO(self.get_string(key).replace('\n',
                                                               os.linesep))
 
     def get_labels(self):
@@ -1259,7 +1259,7 @@
         else:
             self._file.write('1,,' + os.linesep)
         if isinstance(message, email.message.Message):
-            orig_buffer = StringIO.StringIO()
+            orig_buffer = io.StringIO()
             orig_generator = email.generator.Generator(orig_buffer, False, 0)
             orig_generator.flatten(message)
             orig_buffer.seek(0)
@@ -1270,7 +1270,7 @@
                     break
             self._file.write('*** EOOH ***' + os.linesep)
             if isinstance(message, BabylMessage):
-                vis_buffer = StringIO.StringIO()
+                vis_buffer = io.StringIO()
                 vis_generator = email.generator.Generator(vis_buffer, False, 0)
                 vis_generator.flatten(message.get_visible())
                 while True:
diff --git a/Lib/mimetools.py b/Lib/mimetools.py
index 8c1cc19..45d9d32 100644
--- a/Lib/mimetools.py
+++ b/Lib/mimetools.py
@@ -144,6 +144,7 @@
 
 
 # Subroutines for decoding some common content-transfer-types
+# Input and output must be files opened in binary mode
 
 def decode(input, output, encoding):
     """Decode common content-transfer-encodings (base64, quopri, uuencode)."""
@@ -157,7 +158,7 @@
         import uu
         return uu.decode(input, output)
     if encoding in ('7bit', '8bit'):
-        return output.write(input.read())
+        return output.write(input.read().decode("Latin-1"))
     if encoding in decodetab:
         pipethrough(input, decodetab[encoding], output)
     else:
diff --git a/Lib/optparse.py b/Lib/optparse.py
index e648a28..84a6abd 100644
--- a/Lib/optparse.py
+++ b/Lib/optparse.py
@@ -1621,13 +1621,6 @@
         result.append(self.format_epilog(formatter))
         return "".join(result)
 
-    # used by test suite
-    def _get_encoding(self, file):
-        encoding = getattr(file, "encoding", None)
-        if not encoding:
-            encoding = sys.getdefaultencoding()
-        return encoding
-
     def print_help(self, file=None):
         """print_help(file : file = stdout)
 
@@ -1636,8 +1629,7 @@
         """
         if file is None:
             file = sys.stdout
-        encoding = self._get_encoding(file)
-        file.write(self.format_help().encode(encoding, "replace"))
+        file.write(self.format_help())
 
 # class OptionParser
 
diff --git a/Lib/pickletools.py b/Lib/pickletools.py
index 8c324c7..f3e8fbc 100644
--- a/Lib/pickletools.py
+++ b/Lib/pickletools.py
@@ -1797,8 +1797,8 @@
     is None.
 
     If the pickle has a tell() method, pos was the value of pickle.tell()
-    before reading the current opcode.  If the pickle is a string object,
-    it's wrapped in a StringIO object, and the latter's tell() result is
+    before reading the current opcode.  If the pickle is a bytes object,
+    it's wrapped in a BytesIO object, and the latter's tell() result is
     used.  Else (the pickle doesn't have a tell(), and it's not obvious how
     to query its current position) pos is None.
     """
diff --git a/Lib/plat-mac/aepack.py b/Lib/plat-mac/aepack.py
index aa0f2cd..726a7de 100644
--- a/Lib/plat-mac/aepack.py
+++ b/Lib/plat-mac/aepack.py
@@ -17,7 +17,7 @@
 from Carbon.AppleEvents import *
 import MacOS
 import Carbon.File
-import StringIO
+import io
 import aetypes
 from aetypes import mkenum, ObjectSpecifier
 import os
diff --git a/Lib/plat-mac/gensuitemodule.py b/Lib/plat-mac/gensuitemodule.py
index 10a996f..b487f55 100644
--- a/Lib/plat-mac/gensuitemodule.py
+++ b/Lib/plat-mac/gensuitemodule.py
@@ -12,7 +12,7 @@
 import string
 import sys
 import types
-import StringIO
+import io
 import keyword
 import macresource
 import aetools
@@ -266,7 +266,7 @@
 
 def decode(data, verbose=None):
     """Decode a resource into a python data structure"""
-    f = StringIO.StringIO(data)
+    f = io.StringIO(data)
     aete = generic(getaete, f)
     aete = simplify(aete)
     processed = f.tell()
diff --git a/Lib/pprint.py b/Lib/pprint.py
index d7f9a28..6449868 100644
--- a/Lib/pprint.py
+++ b/Lib/pprint.py
@@ -36,7 +36,7 @@
 
 import sys as _sys
 
-from StringIO import StringIO as _StringIO
+from io import StringIO as _StringIO
 
 __all__ = ["pprint","pformat","isreadable","isrecursive","saferepr",
            "PrettyPrinter"]
diff --git a/Lib/pydoc.py b/Lib/pydoc.py
index f8fafa3..eea9853 100755
--- a/Lib/pydoc.py
+++ b/Lib/pydoc.py
@@ -1804,8 +1804,8 @@
         document = re.sub(addrpat, '', re.sub(divpat, '', file.read()))
         file.close()
 
-        import htmllib, formatter, StringIO
-        buffer = StringIO.StringIO()
+        import htmllib, formatter, io
+        buffer = io.StringIO()
         parser = htmllib.HTMLParser(
             formatter.AbstractFormatter(formatter.DumbWriter(buffer)))
         parser.start_table = parser.do_p
@@ -1816,7 +1816,7 @@
         buffer = replace(buffer.getvalue(), '\xa0', ' ', '\n', '\n  ')
         pager('  ' + buffer.strip() + '\n')
         if xrefs:
-            buffer = StringIO.StringIO()
+            buffer = io.StringIO()
             formatter.DumbWriter(buffer).send_flowing_data(
                 'Related help topics: ' + ', '.join(xrefs.split()) + '\n')
             self.output.write('\n%s\n' % buffer.getvalue())
@@ -1900,9 +1900,9 @@
             else:
                 loader = importer.find_module(modname)
                 if hasattr(loader,'get_source'):
-                    import StringIO
+                    import io
                     desc = source_synopsis(
-                        StringIO.StringIO(loader.get_source(modname))
+                        io.StringIO(loader.get_source(modname))
                     ) or ''
                     if hasattr(loader,'get_filename'):
                         path = loader.get_filename(modname)
diff --git a/Lib/test/pickletester.py b/Lib/test/pickletester.py
index 7bff76f..0ad1f48 100644
--- a/Lib/test/pickletester.py
+++ b/Lib/test/pickletester.py
@@ -406,7 +406,7 @@
     # is a mystery.  cPickle also suppresses PUT for objects with a refcount
     # of 1.
     def dont_test_disassembly(self):
-        from cStringIO import StringIO
+        from io import StringIO
         from pickletools import dis
 
         for proto, expected in (0, DATA0_DIS), (1, DATA1_DIS):
@@ -951,8 +951,8 @@
         self.assertEqual(self.module.HIGHEST_PROTOCOL, 2)
 
     def test_callapi(self):
-        from cStringIO import StringIO
-        f = StringIO()
+        from io import BytesIO
+        f = BytesIO()
         # With and without keyword arguments
         self.module.dump(123, f, -1)
         self.module.dump(123, file=f, protocol=-1)
diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 28b82ad..31e4eaf 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -125,7 +125,7 @@
 import random
 import warnings
 import re
-import StringIO
+import io
 import traceback
 
 # I see no other way to suppress these warnings;
@@ -537,7 +537,7 @@
     if verbose:
         cfp = None
     else:
-        cfp = StringIO.StringIO()  # XXX Should use io.StringIO()
+        cfp = io.StringIO()  # XXX Should use io.StringIO()
 
     try:
         save_stdout = sys.stdout
diff --git a/Lib/test/test_StringIO.py b/Lib/test/test_StringIO.py
index 2f4a221..4f3ce83 100644
--- a/Lib/test/test_StringIO.py
+++ b/Lib/test/test_StringIO.py
@@ -2,13 +2,13 @@
 
 import sys
 import unittest
-import StringIO
-import cStringIO
+import io
 from test import test_support
 
 
 class TestGenericStringIO:
-    # use a class variable MODULE to define which module is being tested
+    # use a class variable CLASS to define which class is being tested
+    CLASS = None
 
     # Line of data to test as string
     _line = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!'
@@ -20,7 +20,7 @@
     def setUp(self):
         self._line = self.constructor(self._line)
         self._lines = self.constructor((self._line + '\n') * 5)
-        self._fp = self.MODULE.StringIO(self._lines)
+        self._fp = self.CLASS(self._lines)
 
     def test_reads(self):
         eq = self.assertEqual
@@ -30,7 +30,7 @@
         eq(len(self._fp.readlines(60)), 2)
 
     def test_writes(self):
-        f = self.MODULE.StringIO()
+        f = self.CLASS()
         self.assertRaises(TypeError, f.seek)
         f.write(self._line[:6])
         f.seek(3)
@@ -39,7 +39,7 @@
         self.assertEqual(f.getvalue(), 'abcuvwxyz!')
 
     def test_writelines(self):
-        f = self.MODULE.StringIO()
+        f = self.CLASS()
         f.writelines([self._line[0], self._line[1], self._line[2]])
         f.seek(0)
         self.assertEqual(f.getvalue(), 'abc')
@@ -48,12 +48,12 @@
         def errorGen():
             yield 'a'
             raise KeyboardInterrupt()
-        f = self.MODULE.StringIO()
+        f = self.CLASS()
         self.assertRaises(KeyboardInterrupt, f.writelines, errorGen())
 
     def test_truncate(self):
         eq = self.assertEqual
-        f = self.MODULE.StringIO()
+        f = self.CLASS()
         f.write(self._lines)
         f.seek(10)
         f.truncate()
@@ -62,22 +62,22 @@
         eq(f.getvalue(), 'abcde')
         f.write('xyz')
         eq(f.getvalue(), 'abcdexyz')
-        self.assertRaises(IOError, f.truncate, -1)
+        self.assertRaises(ValueError, f.truncate, -1)
         f.close()
         self.assertRaises(ValueError, f.write, 'frobnitz')
 
     def test_closed_flag(self):
-        f = self.MODULE.StringIO()
+        f = self.CLASS()
         self.assertEqual(f.closed, False)
         f.close()
         self.assertEqual(f.closed, True)
-        f = self.MODULE.StringIO(self.constructor("abc"))
+        f = self.CLASS(self.constructor("abc"))
         self.assertEqual(f.closed, False)
         f.close()
         self.assertEqual(f.closed, True)
 
     def test_isatty(self):
-        f = self.MODULE.StringIO()
+        f = self.CLASS()
         self.assertRaises(TypeError, f.isatty, None)
         self.assertEqual(f.isatty(), False)
         f.close()
@@ -96,10 +96,10 @@
             i += 1
         eq(i, 5)
         self._fp.close()
-        self.assertRaises(ValueError, next, self._fp)
+        self.assertRaises(StopIteration, next, self._fp)
 
-class TestStringIO(TestGenericStringIO, unittest.TestCase):
-    MODULE = StringIO
+class TestioStringIO(TestGenericStringIO, unittest.TestCase):
+    CLASS = io.StringIO
 
     def test_unicode(self):
 
@@ -109,7 +109,7 @@
         # snippets to larger Unicode strings. This is tested by this
         # method. Note that cStringIO does not support this extension.
 
-        f = self.MODULE.StringIO()
+        f = self.CLASS()
         f.write(self._line[:6])
         f.seek(3)
         f.write(str(self._line[20:26]))
@@ -118,55 +118,10 @@
         self.assertEqual(s, str('abcuvwxyz!'))
         self.assertEqual(type(s), str)
 
-class TestcStringIO(TestGenericStringIO, unittest.TestCase):
-    MODULE = cStringIO
-    constructor = str8
-
-    def test_unicode(self):
-
-        if not test_support.have_unicode: return
-
-        # The cStringIO module converts Unicode strings to character
-        # strings when writing them to cStringIO objects.
-        # Check that this works.
-
-        f = self.MODULE.StringIO()
-        f.write(str(self._line[:5]))
-        s = f.getvalue()
-        self.assertEqual(s, 'abcde')
-        self.assertEqual(type(s), str8)
-
-        f = self.MODULE.StringIO(str(self._line[:5]))
-        s = f.getvalue()
-        self.assertEqual(s, 'abcde')
-        self.assertEqual(type(s), str8)
-
-        # XXX This no longer fails -- the default encoding is always UTF-8.
-        ##self.assertRaises(UnicodeDecodeError, self.MODULE.StringIO, '\xf4')
-
-class TestBufferStringIO(TestStringIO):
-
-    def constructor(self, s):
-        return buffer(str8(s))
-
-class TestBuffercStringIO(TestcStringIO):
-
-    def constructor(self, s):
-        return buffer(str8(s))
-
 
 def test_main():
-    classes = [
-        TestStringIO,
-        TestcStringIO,
-        ]
-    if not sys.platform.startswith('java'):
-        classes.extend([
-        TestBufferStringIO,
-        TestBuffercStringIO
-        ])
-    test_support.run_unittest(*classes)
+    test_support.run_unittest(TestioStringIO)
 
 
 if __name__ == '__main__':
-    unittest.main()
+    test_main()
diff --git a/Lib/test/test___all__.py b/Lib/test/test___all__.py
index 4cf2e25..99bc330 100644
--- a/Lib/test/test___all__.py
+++ b/Lib/test/test___all__.py
@@ -36,7 +36,6 @@
         self.check_all("Queue")
         self.check_all("SimpleHTTPServer")
         self.check_all("SocketServer")
-        self.check_all("StringIO")
         self.check_all("UserString")
         self.check_all("aifc")
         self.check_all("base64")
diff --git a/Lib/test/test_atexit.py b/Lib/test/test_atexit.py
index 142e543..76a5036 100644
--- a/Lib/test/test_atexit.py
+++ b/Lib/test/test_atexit.py
@@ -1,6 +1,6 @@
 import sys
 import unittest
-import StringIO
+import io
 import atexit
 from test import test_support
 
@@ -25,7 +25,7 @@
 
 class TestCase(unittest.TestCase):
     def setUp(self):
-        self.stream = StringIO.StringIO()
+        self.stream = io.StringIO()
         sys.stdout = sys.stderr = self.stream
         atexit._clear()
 
diff --git a/Lib/test/test_base64.py b/Lib/test/test_base64.py
index 2f592f1..6f88695 100644
--- a/Lib/test/test_base64.py
+++ b/Lib/test/test_base64.py
@@ -36,23 +36,23 @@
 
     def test_encode(self):
         eq = self.assertEqual
-        from cStringIO import StringIO
-        infp = StringIO('abcdefghijklmnopqrstuvwxyz'
-                        'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
-                        '0123456789!@#0^&*();:<>,. []{}')
-        outfp = StringIO()
+        from io import BytesIO
+        infp = BytesIO(b'abcdefghijklmnopqrstuvwxyz'
+                       b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+                       b'0123456789!@#0^&*();:<>,. []{}')
+        outfp = BytesIO()
         base64.encode(infp, outfp)
         eq(outfp.getvalue(),
-           'YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXpBQkNE'
-           'RUZHSElKS0xNTk9QUVJTVFVWV1hZWjAxMjM0\nNT'
-           'Y3ODkhQCMwXiYqKCk7Ojw+LC4gW117fQ==\n')
+           b'YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXpBQkNE'
+           b'RUZHSElKS0xNTk9QUVJTVFVWV1hZWjAxMjM0\nNT'
+           b'Y3ODkhQCMwXiYqKCk7Ojw+LC4gW117fQ==\n')
 
     def test_decode(self):
-        from cStringIO import StringIO
-        infp = StringIO('d3d3LnB5dGhvbi5vcmc=')
-        outfp = StringIO()
+        from io import BytesIO
+        infp = BytesIO(b'd3d3LnB5dGhvbi5vcmc=')
+        outfp = BytesIO()
         base64.decode(infp, outfp)
-        self.assertEqual(outfp.getvalue(), 'www.python.org')
+        self.assertEqual(outfp.getvalue(), b'www.python.org')
 
 
 
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 7e37c29..a4ae21a 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -5,7 +5,7 @@
                               run_with_locale
 from operator import neg
 
-import sys, warnings, cStringIO, random, UserDict
+import sys, warnings, random, UserDict, io
 warnings.filterwarnings("ignore", "hex../oct.. of negative int",
                         FutureWarning, __name__)
 warnings.filterwarnings("ignore", "integer argument expected",
@@ -1455,11 +1455,11 @@
             self.assertRaises(ValueError, input)
 
             sys.stdout = BitBucket()
-            sys.stdin = cStringIO.StringIO("NULL\0")
+            sys.stdin = io.StringIO("NULL\0")
             self.assertRaises(TypeError, input, 42, 42)
-            sys.stdin = cStringIO.StringIO("    'whitespace'")
+            sys.stdin = io.StringIO("    'whitespace'")
             self.assertEqual(input(), "    'whitespace'")
-            sys.stdin = cStringIO.StringIO()
+            sys.stdin = io.StringIO()
             self.assertRaises(EOFError, input)
 
             del sys.stdout
diff --git a/Lib/test/test_bz2.py b/Lib/test/test_bz2.py
index 06293f5..32c9cef 100644
--- a/Lib/test/test_bz2.py
+++ b/Lib/test/test_bz2.py
@@ -3,7 +3,7 @@
 from test.test_support import TESTFN
 
 import unittest
-from cStringIO import StringIO
+from io import BytesIO
 import os
 import subprocess
 import sys
@@ -98,7 +98,7 @@
         self.createTempFile()
         bz2f = BZ2File(self.filename)
         self.assertRaises(TypeError, bz2f.readline, None)
-        sio = StringIO(self.TEXT)
+        sio = BytesIO(self.TEXT)
         for line in sio.readlines():
             self.assertEqual(bz2f.readline(), line)
         bz2f.close()
@@ -108,7 +108,7 @@
         self.createTempFile()
         bz2f = BZ2File(self.filename)
         self.assertRaises(TypeError, bz2f.readlines, None)
-        sio = StringIO(self.TEXT)
+        sio = BytesIO(self.TEXT)
         self.assertEqual(bz2f.readlines(), sio.readlines())
         bz2f.close()
 
@@ -116,7 +116,7 @@
         # "Test iter(BZ2File)"
         self.createTempFile()
         bz2f = BZ2File(self.filename)
-        sio = StringIO(self.TEXT)
+        sio = BytesIO(self.TEXT)
         self.assertEqual(list(iter(bz2f)), sio.readlines())
         bz2f.close()
 
@@ -149,7 +149,7 @@
         # "Test BZ2File.writelines()"
         bz2f = BZ2File(self.filename, "w")
         self.assertRaises(TypeError, bz2f.writelines)
-        sio = StringIO(self.TEXT)
+        sio = BytesIO(self.TEXT)
         bz2f.writelines(sio.readlines())
         bz2f.close()
         # patch #1535500
diff --git a/Lib/test/test_cfgparser.py b/Lib/test/test_cfgparser.py
index 076de4a..8822735 100644
--- a/Lib/test/test_cfgparser.py
+++ b/Lib/test/test_cfgparser.py
@@ -1,5 +1,5 @@
 import ConfigParser
-import StringIO
+import io
 import unittest
 import UserDict
 
@@ -30,7 +30,7 @@
 
     def fromstring(self, string, defaults=None):
         cf = self.newconfig(defaults)
-        sio = StringIO.StringIO(string)
+        sio = io.StringIO(string)
         cf.readfp(sio)
         return cf
 
@@ -156,7 +156,7 @@
                          "No Section!\n")
 
     def parse_error(self, exc, src):
-        sio = StringIO.StringIO(src)
+        sio = io.StringIO(src)
         self.assertRaises(exc, self.cf.readfp, sio)
 
     def test_query_errors(self):
@@ -222,7 +222,7 @@
             "foo: another very\n"
             " long line"
             )
-        output = StringIO.StringIO()
+        output = io.StringIO()
         cf.write(output)
         self.assertEqual(
             output.getvalue(),
@@ -449,7 +449,7 @@
                         "o1=4\n"
                         "[a]\n"
                         "k=v\n")
-        output = StringIO.StringIO()
+        output = io.StringIO()
         self.cf.write(output)
         self.assertEquals(output.getvalue(),
                           "[a]\n"
diff --git a/Lib/test/test_cgi.py b/Lib/test/test_cgi.py
index 6d5bfd6..652b36e 100644
--- a/Lib/test/test_cgi.py
+++ b/Lib/test/test_cgi.py
@@ -4,7 +4,7 @@
 import sys
 import tempfile
 import unittest
-from StringIO import StringIO
+from io import StringIO
 
 class HackedSysModule:
     # The regression test will have real values in sys.argv, which
@@ -15,9 +15,9 @@
 cgi.sys = HackedSysModule()
 
 try:
-    from cStringIO import StringIO
+    from io import StringIO
 except ImportError:
-    from StringIO import StringIO
+    from io import StringIO
 
 class ComparableException:
     def __init__(self, err):
diff --git a/Lib/test/test_codeop.py b/Lib/test/test_codeop.py
index b3fd18a..edea601 100644
--- a/Lib/test/test_codeop.py
+++ b/Lib/test/test_codeop.py
@@ -6,10 +6,10 @@
 from test.test_support import run_unittest, is_jython
 
 from codeop import compile_command, PyCF_DONT_IMPLY_DEDENT
+import io
 
 if is_jython:
     import sys
-    import cStringIO
 
     def unify_callables(d):
         for n,v in d.items():
@@ -27,7 +27,7 @@
             if symbol == "single":
                 d,r = {},{}
                 saved_stdout = sys.stdout
-                sys.stdout = cStringIO.StringIO()
+                sys.stdout = io.StringIO()
                 try:
                     exec(code, d)
                     exec(compile(str,"<input>","single"), r)
diff --git a/Lib/test/test_cookielib.py b/Lib/test/test_cookielib.py
index d72a3a8..87f118d 100644
--- a/Lib/test/test_cookielib.py
+++ b/Lib/test/test_cookielib.py
@@ -153,8 +153,8 @@
             try:
                 result = split_header_words([arg])
             except:
-                import traceback, StringIO
-                f = StringIO.StringIO()
+                import traceback, io
+                f = io.StringIO()
                 traceback.print_exc(None, f)
                 result = "(error -- traceback follows)\n\n%s" % f.getvalue()
             self.assertEquals(result,  expect, """
@@ -204,8 +204,8 @@
         """
         headers: list of RFC822-style 'Key: value' strings
         """
-        import mimetools, StringIO
-        f = StringIO.StringIO("\n".join(headers))
+        import mimetools, io
+        f = io.StringIO("\n".join(headers))
         self._headers = mimetools.Message(f)
         self._url = url
     def info(self): return self._headers
diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index 6098285..21cc408 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -5,7 +5,7 @@
 import sys
 import os
 import unittest
-from StringIO import StringIO
+from io import StringIO
 from tempfile import TemporaryFile
 import csv
 import gc
diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index 63391af..d51a865 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -4,7 +4,7 @@
 from weakref import proxy
 import copy
 import pickle
-from cStringIO import StringIO
+from io import StringIO
 import random
 import os
 
diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index d98c607..c016681 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -1,7 +1,7 @@
 import unittest
 from test import test_support
 
-import sys, UserDict, cStringIO
+import sys, UserDict
 
 
 class DictTest(unittest.TestCase):
diff --git a/Lib/test/test_dis.py b/Lib/test/test_dis.py
index f1bd3e7..f135780 100644
--- a/Lib/test/test_dis.py
+++ b/Lib/test/test_dis.py
@@ -4,7 +4,7 @@
 import unittest
 import sys
 import dis
-import StringIO
+import io
 
 
 def _f(a):
@@ -103,7 +103,7 @@
 
 class DisTests(unittest.TestCase):
     def do_disassembly_test(self, func, expected):
-        s = StringIO.StringIO()
+        s = io.StringIO()
         save_stdout = sys.stdout
         sys.stdout = s
         dis.dis(func)
diff --git a/Lib/test/test_doctest.py b/Lib/test/test_doctest.py
index 5307395..dea03d3 100644
--- a/Lib/test/test_doctest.py
+++ b/Lib/test/test_doctest.py
@@ -2405,7 +2405,7 @@
     from test import test_doctest
     test_support.run_doctest(test_doctest, verbosity=True)
 
-import trace, sys, re, StringIO
+import trace, sys, re, io
 def test_coverage(coverdir):
     tracer = trace.Trace(ignoredirs=[sys.prefix, sys.exec_prefix,],
                          trace=0, count=1)
diff --git a/Lib/test/test_fileinput.py b/Lib/test/test_fileinput.py
index e0b5818..a9d2fa6 100644
--- a/Lib/test/test_fileinput.py
+++ b/Lib/test/test_fileinput.py
@@ -7,7 +7,7 @@
 from test.test_support import verbose, TESTFN, run_unittest
 from test.test_support import unlink as safe_unlink
 import sys, os, re
-from StringIO import StringIO
+from io import StringIO
 from fileinput import FileInput, hook_encoded
 
 # The fileinput module has 2 interfaces: the FileInput class which does
diff --git a/Lib/test/test_generators.py b/Lib/test/test_generators.py
index a1ab0f1..4710c8c 100644
--- a/Lib/test/test_generators.py
+++ b/Lib/test/test_generators.py
@@ -1685,8 +1685,8 @@
 
 Our ill-behaved code should be invoked during GC:
 
->>> import sys, StringIO
->>> old, sys.stderr = sys.stderr, StringIO.StringIO()
+>>> import sys, io
+>>> old, sys.stderr = sys.stderr, io.StringIO()
 >>> g = f()
 >>> next(g)
 >>> del g
@@ -1796,10 +1796,10 @@
 printing warnings and to doublecheck that we actually tested what we wanted
 to test.
 
->>> import sys, StringIO
+>>> import sys, io
 >>> old = sys.stderr
 >>> try:
-...     sys.stderr = StringIO.StringIO()
+...     sys.stderr = io.StringIO()
 ...     class Leaker:
 ...         def __del__(self):
 ...             raise RuntimeError
diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index 953acad..1073cdd 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -25,7 +25,7 @@
 """
 
 import select
-import os, sys, struct, pickle, cStringIO
+import os, sys, struct, pickle, io
 import socket, tempfile, threading, time
 import logging, logging.handlers, logging.config
 from test.test_support import run_with_locale
@@ -606,7 +606,7 @@
     #Configure the logger for logrecv so events do not propagate beyond it.
     #The sockLogger output is buffered in memory until the end of the test,
     #and printed at the end.
-    sockOut = cStringIO.StringIO()
+    sockOut = io.StringIO()
     sockLogger = logging.getLogger("logrecv")
     sockLogger.setLevel(logging.DEBUG)
     sockhdlr = logging.StreamHandler(sockOut)
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 4761aa7..59def94 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -7,7 +7,7 @@
 import email.message
 import rfc822
 import re
-import StringIO
+import io
 from test import test_support
 import unittest
 import mailbox
@@ -69,7 +69,7 @@
         self.assertEqual(len(self._box), 2)
         keys.append(self._box.add(email.message_from_string(_sample_message)))
         self.assertEqual(len(self._box), 3)
-        keys.append(self._box.add(StringIO.StringIO(_sample_message)))
+        keys.append(self._box.add(io.StringIO(_sample_message)))
         self.assertEqual(len(self._box), 4)
         keys.append(self._box.add(_sample_message))
         self.assertEqual(len(self._box), 5)
@@ -400,12 +400,12 @@
     def test_dump_message(self):
         # Write message representations to disk
         for input in (email.message_from_string(_sample_message),
-                      _sample_message, StringIO.StringIO(_sample_message)):
-            output = StringIO.StringIO()
+                      _sample_message, io.StringIO(_sample_message)):
+            output = io.StringIO()
             self._box._dump_message(input, output)
             self.assert_(output.getvalue() ==
                          _sample_message.replace('\n', os.linesep))
-        output = StringIO.StringIO()
+        output = io.StringIO()
         self.assertRaises(TypeError,
                           lambda: self._box._dump_message(None, output))
 
diff --git a/Lib/test/test_mhlib.py b/Lib/test/test_mhlib.py
index 1b1af6a..ad66ede 100644
--- a/Lib/test/test_mhlib.py
+++ b/Lib/test/test_mhlib.py
@@ -8,7 +8,8 @@
 
 import unittest
 from test.test_support import run_unittest, TESTFN, TestSkipped
-import os, StringIO
+import os
+import io
 import sys
 import mhlib
 
@@ -262,7 +263,7 @@
         f = mh.openfolder('dummy1')
         def create(n):
             msg = "From: foo\nSubject: %s\n\nDummy Message %s\n" % (n,n)
-            f.createmessage(n, StringIO.StringIO(msg))
+            f.createmessage(n, io.StringIO(msg))
 
         create(7)
         create(8)
diff --git a/Lib/test/test_mimetools.py b/Lib/test/test_mimetools.py
index ad24776..cf0e191 100644
--- a/Lib/test/test_mimetools.py
+++ b/Lib/test/test_mimetools.py
@@ -1,28 +1,54 @@
 import unittest
 from test import test_support
 
-import string, StringIO, mimetools
+import string, mimetools
+import io
 
-msgtext1 = mimetools.Message(StringIO.StringIO(
+msgtext1 = mimetools.Message(io.StringIO(
 """Content-Type: text/plain; charset=iso-8859-1; format=flowed
 Content-Transfer-Encoding: 8bit
 
 Foo!
 """))
 
+sample = bytes(string.ascii_letters + "=" + string.digits + "\n", "ASCII")
+
 class MimeToolsTest(unittest.TestCase):
 
-    def test_decodeencode(self):
-        start = string.ascii_letters + "=" + string.digits + "\n"
-        for enc in ['7bit','8bit','base64','quoted-printable',
-                    'uuencode', 'x-uuencode', 'uue', 'x-uue']:
-            i = StringIO.StringIO(start)
-            o = StringIO.StringIO()
-            mimetools.encode(i, o, enc)
-            i = StringIO.StringIO(o.getvalue())
-            o = StringIO.StringIO()
-            mimetools.decode(i, o, enc)
-            self.assertEqual(o.getvalue(), start)
+    def decode_encode_test(self, enc):
+        i = io.BytesIO(sample)
+        o = io.BytesIO()
+        mimetools.encode(i, o, enc)
+        i = io.BytesIO(o.getvalue())
+        o = io.BytesIO()
+        mimetools.decode(i, o, enc)
+        self.assertEqual(o.getvalue(), sample)
+
+    # Separate tests for better diagnostics
+
+    def test_7bit(self):
+        self.decode_encode_test('7bit')
+
+    def test_8bit(self):
+        self.decode_encode_test('8bit')
+
+    def test_base64(self):
+        self.decode_encode_test('base64')
+
+    def test_quoted_printable(self):
+        self.decode_encode_test('quoted-printable')
+
+    def test_uuencode(self):
+        self.decode_encode_test('uuencode')
+
+    def test_x_uuencode(self):
+        self.decode_encode_test('x-uuencode')
+
+    def test_uue(self):
+        self.decode_encode_test('uue')
+
+    def test_x_uue(self):
+        self.decode_encode_test('x-uue')
 
     def test_boundary(self):
         s = set([""])
@@ -32,7 +58,7 @@
             s.add(nb)
 
     def test_message(self):
-        msg = mimetools.Message(StringIO.StringIO(msgtext1))
+        msg = mimetools.Message(io.StringIO(msgtext1))
         self.assertEqual(msg.gettype(), "text/plain")
         self.assertEqual(msg.getmaintype(), "text")
         self.assertEqual(msg.getsubtype(), "plain")
diff --git a/Lib/test/test_mimetypes.py b/Lib/test/test_mimetypes.py
index 0190c2f..53de072 100644
--- a/Lib/test/test_mimetypes.py
+++ b/Lib/test/test_mimetypes.py
@@ -1,5 +1,5 @@
 import mimetypes
-import StringIO
+import io
 import unittest
 
 from test import test_support
@@ -30,7 +30,7 @@
 
     def test_file_parsing(self):
         eq = self.assertEqual
-        sio = StringIO.StringIO("x-application/x-unittest pyunit\n")
+        sio = io.StringIO("x-application/x-unittest pyunit\n")
         self.db.readfp(sio)
         eq(self.db.guess_type("foo.pyunit"),
            ("x-application/x-unittest", None))
diff --git a/Lib/test/test_minidom.py b/Lib/test/test_minidom.py
index cc637d0..fb3b098 100644
--- a/Lib/test/test_minidom.py
+++ b/Lib/test/test_minidom.py
@@ -4,7 +4,7 @@
 import sys
 import pickle
 import traceback
-from StringIO import StringIO
+from io import StringIO
 from test.test_support import verbose, run_unittest, TestSkipped
 import unittest
 
diff --git a/Lib/test/test_multifile.py b/Lib/test/test_multifile.py
index 437c394..b29137c 100644
--- a/Lib/test/test_multifile.py
+++ b/Lib/test/test_multifile.py
@@ -1,6 +1,6 @@
 import mimetools
 import multifile
-import cStringIO
+import io
 
 msg = """Mime-Version: 1.0
 Content-Type: multipart/mixed;
@@ -57,7 +57,7 @@
     global boundaries, linecount
     boundaries = 0
     linecount = 0
-    f = cStringIO.StringIO(msg)
+    f = io.StringIO(msg)
     getMIMEMsg(multifile.MultiFile(f))
     assert boundaries == 2
     assert linecount == 9
diff --git a/Lib/test/test_optparse.py b/Lib/test/test_optparse.py
index 2bae0a6..1cfdd50 100644
--- a/Lib/test/test_optparse.py
+++ b/Lib/test/test_optparse.py
@@ -14,7 +14,7 @@
 import copy
 import unittest
 
-from StringIO import StringIO
+from io import StringIO
 from pprint import pprint
 from test import test_support
 
@@ -157,12 +157,9 @@
                      expected_error=None):
         """Assert the parser prints the expected output on stdout."""
         save_stdout = sys.stdout
-        encoding = getattr(save_stdout, 'encoding', None)
         try:
             try:
                 sys.stdout = StringIO()
-                if encoding:
-                    sys.stdout.encoding = encoding
                 self.parser.parse_args(cmdline_args)
             finally:
                 output = sys.stdout.getvalue()
diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py
index 28ad055..faa5523 100644
--- a/Lib/test/test_peepholer.py
+++ b/Lib/test/test_peepholer.py
@@ -1,6 +1,6 @@
 import dis
 import sys
-from cStringIO import StringIO
+from io import StringIO
 import unittest
 
 def disassemble(func):
diff --git a/Lib/test/test_rfc822.py b/Lib/test/test_rfc822.py
index c355950..b563c9c 100644
--- a/Lib/test/test_rfc822.py
+++ b/Lib/test/test_rfc822.py
@@ -4,9 +4,9 @@
 from test import test_support
 
 try:
-    from cStringIO import StringIO
+    from io import StringIO
 except ImportError:
-    from StringIO import StringIO
+    from io import StringIO
 
 
 class MessageTestCase(unittest.TestCase):
diff --git a/Lib/test/test_robotparser.py b/Lib/test/test_robotparser.py
index 666d00a..e1e8055 100644
--- a/Lib/test/test_robotparser.py
+++ b/Lib/test/test_robotparser.py
@@ -1,4 +1,5 @@
-import unittest, StringIO, robotparser
+import unittest, robotparser
+import io
 from test import test_support
 
 class RobotTestCase(unittest.TestCase):
@@ -32,7 +33,7 @@
 def RobotTest(index, robots_txt, good_urls, bad_urls,
               agent="test_robotparser"):
 
-    lines = StringIO.StringIO(robots_txt).readlines()
+    lines = io.StringIO(robots_txt).readlines()
     parser = robotparser.RobotFileParser()
     parser.parse(lines)
     for url in good_urls:
diff --git a/Lib/test/test_sax.py b/Lib/test/test_sax.py
index 0d76cbb..e2639fa 100644
--- a/Lib/test/test_sax.py
+++ b/Lib/test/test_sax.py
@@ -12,7 +12,7 @@
                              XMLFilterBase
 from xml.sax.expatreader import create_parser
 from xml.sax.xmlreader import InputSource, AttributesImpl, AttributesNSImpl
-from cStringIO import StringIO
+from io import StringIO
 from test.test_support import findfile, run_unittest
 import unittest
 import os
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 7d7a09b..d9adf02 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -1,13 +1,13 @@
 # -*- coding: iso-8859-1 -*-
 import unittest, test.test_support
-import sys, cStringIO
+import sys, io
 
 class SysModuleTest(unittest.TestCase):
 
     def test_original_displayhook(self):
         import __builtin__
         savestdout = sys.stdout
-        out = cStringIO.StringIO()
+        out = io.StringIO()
         sys.stdout = out
 
         dh = sys.__displayhook__
@@ -46,7 +46,7 @@
 
     def test_original_excepthook(self):
         savestderr = sys.stderr
-        err = cStringIO.StringIO()
+        err = io.StringIO()
         sys.stderr = err
 
         eh = sys.__excepthook__
diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index ea32ef5..0585131 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -3,7 +3,7 @@
 import io
 import shutil
 import tempfile
-import StringIO
+import io
 from hashlib import md5
 import errno
 
@@ -897,15 +897,15 @@
         self._test()
 
     def test_empty_fileobj(self):
-        fobj = StringIO.StringIO()
+        fobj = io.BytesIO()
         self._add_testfile(fobj)
         fobj.seek(0)
         self._test(fileobj=fobj)
 
     def test_fileobj(self):
         self._create_testtar()
-        data = open(self.tarname).read()
-        fobj = StringIO.StringIO(data)
+        data = open(self.tarname, "rb").read()
+        fobj = io.BytesIO(data)
         self._add_testfile(fobj)
         fobj.seek(0)
         self._test(names=["foo", "bar"], fileobj=fobj)
diff --git a/Lib/test/test_threadedtempfile.py b/Lib/test/test_threadedtempfile.py
index 753f388..cde15b4 100644
--- a/Lib/test/test_threadedtempfile.py
+++ b/Lib/test/test_threadedtempfile.py
@@ -22,7 +22,7 @@
 
 from test.test_support import threading_setup, threading_cleanup, run_unittest
 import unittest
-import StringIO
+import io
 from traceback import print_exc
 
 startEvent = threading.Event()
@@ -32,7 +32,7 @@
     ok_count = 0
 
     def run(self):
-        self.errors = StringIO.StringIO()
+        self.errors = io.StringIO()
         startEvent.wait()
         for i in range(FILES_PER_THREAD):
             try:
diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
index e3e6de2..91d6ba7 100644
--- a/Lib/test/test_urllib2.py
+++ b/Lib/test/test_urllib2.py
@@ -2,7 +2,7 @@
 from test import test_support
 
 import os, socket
-import StringIO
+import io
 
 import urllib2
 from urllib2 import Request, OpenerDirector
@@ -236,9 +236,9 @@
     def getheaders(self, name):
         return list(self.values())
 
-class MockResponse(StringIO.StringIO):
+class MockResponse(io.StringIO):
     def __init__(self, code, msg, headers, data, url=None):
-        StringIO.StringIO.__init__(self, data)
+        io.StringIO.__init__(self, data)
         self.code, self.msg, self.headers, self.url = code, msg, headers, url
     def info(self):
         return self.headers
@@ -353,7 +353,7 @@
         self.requests = []
     def http_open(self, req):
         import mimetools, httplib, copy
-        from StringIO import StringIO
+        from io import StringIO
         self.requests.append(copy.deepcopy(req))
         if self._count == 0:
             self._count = self._count + 1
@@ -546,7 +546,7 @@
             def __init__(self, data): self.data = data
             def retrfile(self, filename, filetype):
                 self.filename, self.filetype = filename, filetype
-                return StringIO.StringIO(self.data), len(self.data)
+                return io.StringIO(self.data), len(self.data)
 
         class NullFTPHandler(urllib2.FTPHandler):
             def __init__(self, data): self.data = data
diff --git a/Lib/test/test_uu.py b/Lib/test/test_uu.py
index 181e361..4723174 100644
--- a/Lib/test/test_uu.py
+++ b/Lib/test/test_uu.py
@@ -6,47 +6,50 @@
 import unittest
 from test import test_support
 
-import sys, os, uu, cStringIO
+import sys, os
 import uu
-from StringIO import StringIO
+from io import BytesIO
+import io
 
-plaintext = "The smooth-scaled python crept over the sleeping dog\n"
+plaintext = b"The smooth-scaled python crept over the sleeping dog\n"
 
-encodedtext = """\
+encodedtext = b"""\
 M5&AE('-M;V]T:\"US8V%L960@<'ET:&]N(&-R97!T(&]V97(@=&AE('-L965P
 (:6YG(&1O9PH """
 
-encodedtextwrapped = "begin %03o %s\n" + encodedtext.replace("%", "%%") + "\n \nend\n"
+def encodedtextwrapped(mode, filename):
+    return (bytes("begin %03o %s\n" % (mode, filename), "ascii") +
+            encodedtext + b"\n \nend\n")
 
 class UUTest(unittest.TestCase):
 
     def test_encode(self):
-        inp = cStringIO.StringIO(plaintext)
-        out = cStringIO.StringIO()
+        inp = io.BytesIO(plaintext)
+        out = io.BytesIO()
         uu.encode(inp, out, "t1")
-        self.assertEqual(out.getvalue(), encodedtextwrapped % (0o666, "t1"))
-        inp = cStringIO.StringIO(plaintext)
-        out = cStringIO.StringIO()
+        self.assertEqual(out.getvalue(), encodedtextwrapped(0o666, "t1"))
+        inp = io.BytesIO(plaintext)
+        out = io.BytesIO()
         uu.encode(inp, out, "t1", 0o644)
-        self.assertEqual(out.getvalue(), encodedtextwrapped % (0o644, "t1"))
+        self.assertEqual(out.getvalue(), encodedtextwrapped(0o644, "t1"))
 
     def test_decode(self):
-        inp = cStringIO.StringIO(encodedtextwrapped % (0o666, "t1"))
-        out = cStringIO.StringIO()
+        inp = io.BytesIO(encodedtextwrapped(0o666, "t1"))
+        out = io.BytesIO()
         uu.decode(inp, out)
         self.assertEqual(out.getvalue(), plaintext)
-        inp = cStringIO.StringIO(
-            "UUencoded files may contain many lines,\n" +
-            "even some that have 'begin' in them.\n" +
-            encodedtextwrapped % (0o666, "t1")
+        inp = io.BytesIO(
+            b"UUencoded files may contain many lines,\n" +
+            b"even some that have 'begin' in them.\n" +
+            encodedtextwrapped(0o666, "t1")
         )
-        out = cStringIO.StringIO()
+        out = io.BytesIO()
         uu.decode(inp, out)
         self.assertEqual(out.getvalue(), plaintext)
 
     def test_truncatedinput(self):
-        inp = cStringIO.StringIO("begin 644 t1\n" + encodedtext)
-        out = cStringIO.StringIO()
+        inp = io.BytesIO(b"begin 644 t1\n" + encodedtext)
+        out = io.BytesIO()
         try:
             uu.decode(inp, out)
             self.fail("No exception thrown")
@@ -54,8 +57,8 @@
             self.assertEqual(str(e), "Truncated input file")
 
     def test_missingbegin(self):
-        inp = cStringIO.StringIO("")
-        out = cStringIO.StringIO()
+        inp = io.BytesIO(b"")
+        out = io.BytesIO()
         try:
             uu.decode(inp, out)
             self.fail("No exception thrown")
@@ -73,24 +76,27 @@
         sys.stdout = self.stdout
 
     def test_encode(self):
-        sys.stdin = cStringIO.StringIO(plaintext)
-        sys.stdout = cStringIO.StringIO()
+        sys.stdin = io.StringIO(plaintext.decode("ascii"))
+        sys.stdout = io.StringIO()
         uu.encode("-", "-", "t1", 0o666)
-        self.assertEqual(
-            sys.stdout.getvalue(),
-            encodedtextwrapped % (0o666, "t1")
-        )
+        self.assertEqual(sys.stdout.getvalue(),
+                         encodedtextwrapped(0o666, "t1").decode("ascii"))
 
     def test_decode(self):
-        sys.stdin = cStringIO.StringIO(encodedtextwrapped % (0o666, "t1"))
-        sys.stdout = cStringIO.StringIO()
+        sys.stdin = io.StringIO(encodedtextwrapped(0o666, "t1").decode("ascii"))
+        sys.stdout = io.StringIO()
         uu.decode("-", "-")
-        self.assertEqual(sys.stdout.getvalue(), plaintext)
+        stdout = sys.stdout
+        sys.stdout = self.stdout
+        sys.stdin = self.stdin
+        self.assertEqual(stdout.getvalue(), plaintext.decode("ascii"))
 
 class UUFileTest(unittest.TestCase):
 
     def _kill(self, f):
         # close and remove file
+        if f is None:
+            return
         try:
             f.close()
         except (SystemExit, KeyboardInterrupt):
@@ -113,44 +119,46 @@
         del self.tmpout
 
     def test_encode(self):
+        fin = fout = None
         try:
             fin = open(self.tmpin, 'wb')
             fin.write(plaintext)
             fin.close()
 
             fin = open(self.tmpin, 'rb')
-            fout = open(self.tmpout, 'w')
+            fout = open(self.tmpout, 'wb')
             uu.encode(fin, fout, self.tmpin, mode=0o644)
             fin.close()
             fout.close()
 
-            fout = open(self.tmpout, 'r')
+            fout = open(self.tmpout, 'rb')
             s = fout.read()
             fout.close()
-            self.assertEqual(s, encodedtextwrapped % (0o644, self.tmpin))
+            self.assertEqual(s, encodedtextwrapped(0o644, self.tmpin))
 
             # in_file and out_file as filenames
             uu.encode(self.tmpin, self.tmpout, self.tmpin, mode=0o644)
-            fout = open(self.tmpout, 'r')
+            fout = open(self.tmpout, 'rb')
             s = fout.read()
             fout.close()
-            self.assertEqual(s, encodedtextwrapped % (0o644, self.tmpin))
+            self.assertEqual(s, encodedtextwrapped(0o644, self.tmpin))
 
         finally:
             self._kill(fin)
             self._kill(fout)
 
     def test_decode(self):
+        f = None
         try:
-            f = open(self.tmpin, 'w')
-            f.write(encodedtextwrapped % (0o644, self.tmpout))
+            f = open(self.tmpin, 'wb')
+            f.write(encodedtextwrapped(0o644, self.tmpout))
             f.close()
 
-            f = open(self.tmpin, 'r')
+            f = open(self.tmpin, 'rb')
             uu.decode(f)
             f.close()
 
-            f = open(self.tmpout, 'r')
+            f = open(self.tmpout, 'rb')
             s = f.read()
             f.close()
             self.assertEqual(s, plaintext)
@@ -160,21 +168,25 @@
 
     def test_decodetwice(self):
         # Verify that decode() will refuse to overwrite an existing file
+        f = None
         try:
-            f = cStringIO.StringIO(encodedtextwrapped % (0o644, self.tmpout))
+            f = io.BytesIO(encodedtextwrapped(0o644, self.tmpout))
 
-            f = open(self.tmpin, 'r')
+            f = open(self.tmpin, 'rb')
             uu.decode(f)
             f.close()
 
-            f = open(self.tmpin, 'r')
+            f = open(self.tmpin, 'rb')
             self.assertRaises(uu.Error, uu.decode, f)
             f.close()
         finally:
             self._kill(f)
 
 def test_main():
-    test_support.run_unittest(UUTest, UUStdIOTest, UUFileTest)
+    test_support.run_unittest(UUTest,
+                              UUStdIOTest,
+                              UUFileTest,
+                              )
 
 if __name__=="__main__":
     test_main()
diff --git a/Lib/test/test_xml_etree.py b/Lib/test/test_xml_etree.py
index 1c5edd0..c8dd344 100644
--- a/Lib/test/test_xml_etree.py
+++ b/Lib/test/test_xml_etree.py
@@ -39,14 +39,11 @@
     if not hasattr(method, '__call__'):
         print(method, "not callable")
 
-def serialize(ET, elem, encoding=None):
-    import StringIO
-    file = StringIO.StringIO()
+def serialize(ET, elem):
+    import io
     tree = ET.ElementTree(elem)
-    if encoding:
-        tree.write(file, encoding)
-    else:
-        tree.write(file)
+    file = io.StringIO()
+    tree.write(file)
     return file.getvalue()
 
 def summarize(elem):
diff --git a/Lib/test/test_xml_etree_c.py b/Lib/test/test_xml_etree_c.py
index 49cdfde..22d2662 100644
--- a/Lib/test/test_xml_etree_c.py
+++ b/Lib/test/test_xml_etree_c.py
@@ -37,14 +37,11 @@
     if not hasattr(method, '__call__'):
         print(method, "not callable")
 
-def serialize(ET, elem, encoding=None):
-    import StringIO
-    file = StringIO.StringIO()
+def serialize(ET, elem):
+    import io
+    file = io.StringIO()
     tree = ET.ElementTree(elem)
-    if encoding:
-        tree.write(file, encoding)
-    else:
-        tree.write(file)
+    tree.write(file)
     return file.getvalue()
 
 def summarize(elem):
diff --git a/Lib/test/test_zipfile64.py b/Lib/test/test_zipfile64.py
index dedce4a..a008fd0 100644
--- a/Lib/test/test_zipfile64.py
+++ b/Lib/test/test_zipfile64.py
@@ -20,7 +20,7 @@
 import time
 import sys
 
-from StringIO import StringIO
+from io import StringIO
 from tempfile import TemporaryFile
 
 from test.test_support import TESTFN, run_unittest
diff --git a/Lib/test/test_zipimport.py b/Lib/test/test_zipimport.py
index bae2172..f36cbf4 100644
--- a/Lib/test/test_zipimport.py
+++ b/Lib/test/test_zipimport.py
@@ -15,7 +15,7 @@
 import linecache
 import doctest
 import inspect
-import StringIO
+import io
 from traceback import extract_tb, extract_stack, print_tb
 raise_src = 'def do_raise(): raise TypeError\n'
 
@@ -314,7 +314,7 @@
             f,lno,n,line = extract_stack(tb.tb_frame, 1)[0]
             self.assertEqual(line, raise_src.strip())
 
-            s = StringIO.StringIO()
+            s = io.StringIO()
             print_tb(tb, 1, s)
             self.failUnless(s.getvalue().endswith(raise_src))
         else:
diff --git a/Lib/uu.py b/Lib/uu.py
index 97ad9b6..084d9f3 100755
--- a/Lib/uu.py
+++ b/Lib/uu.py
@@ -45,7 +45,7 @@
     # If in_file is a pathname open it and change defaults
     #
     if in_file == '-':
-        in_file = sys.stdin
+        in_file = sys.stdin.buffer
     elif isinstance(in_file, basestring):
         if name is None:
             name = os.path.basename(in_file)
@@ -59,9 +59,9 @@
     # Open out_file if it is a pathname
     #
     if out_file == '-':
-        out_file = sys.stdout
+        out_file = sys.stdout.buffer
     elif isinstance(out_file, basestring):
-        out_file = open(out_file, 'w')
+        out_file = open(out_file, 'wb')
     #
     # Set defaults for name and mode
     #
@@ -86,9 +86,9 @@
     # Open the input file, if needed.
     #
     if in_file == '-':
-        in_file = sys.stdin
+        in_file = sys.stdin.buffer
     elif isinstance(in_file, basestring):
-        in_file = open(in_file)
+        in_file = open(in_file, 'rb')
     #
     # Read until a begin is encountered or we've exhausted the file
     #
@@ -96,17 +96,18 @@
         hdr = in_file.readline()
         if not hdr:
             raise Error('No valid begin line found in input file')
-        if not hdr.startswith('begin'):
+        if not hdr.startswith(b'begin'):
             continue
-        hdrfields = hdr.split(' ', 2)
-        if len(hdrfields) == 3 and hdrfields[0] == 'begin':
+        hdrfields = hdr.split(b' ', 2)
+        if len(hdrfields) == 3 and hdrfields[0] == b'begin':
             try:
                 int(hdrfields[1], 8)
                 break
             except ValueError:
                 pass
     if out_file is None:
-        out_file = hdrfields[2].rstrip()
+        # If the filename isn't ASCII, what's up with that?!?
+        out_file = hdrfields[2].rstrip(b' \t\r\n\f').decode("ascii")
         if os.path.exists(out_file):
             raise Error('Cannot overwrite existing file: %s' % out_file)
     if mode is None:
@@ -116,7 +117,7 @@
     #
     opened = False
     if out_file == '-':
-        out_file = sys.stdout
+        out_file = sys.stdout.buffer
     elif isinstance(out_file, basestring):
         fp = open(out_file, 'wb')
         try:
@@ -129,12 +130,12 @@
     # Main decoding loop
     #
     s = in_file.readline()
-    while s and s.strip() != 'end':
+    while s and s.strip(b' \t\r\n\f') != b'end':
         try:
             data = binascii.a2b_uu(s)
         except binascii.Error as v:
             # Workaround for broken uuencoders by /Fredrik Lundh
-            nbytes = (((ord(s[0])-32) & 63) * 4 + 5) // 3
+            nbytes = (((s[0]-32) & 63) * 4 + 5) // 3
             data = binascii.a2b_uu(s[:nbytes])
             if not quiet:
                 sys.stderr.write("Warning: %s\n" % v)
@@ -158,8 +159,9 @@
         parser.error('incorrect number of arguments')
         sys.exit(1)
 
-    input = sys.stdin
-    output = sys.stdout
+    # Use the binary streams underlying stdin/stdout
+    input = sys.stdin.buffer
+    output = sys.stdout.buffer
     if len(args) > 0:
         input = args[0]
     if len(args) > 1:
@@ -168,7 +170,7 @@
     if options.decode:
         if options.text:
             if isinstance(output, basestring):
-                output = open(output, 'w')
+                output = open(output, 'wb')
             else:
                 print(sys.argv[0], ': cannot do -t to stdout')
                 sys.exit(1)
@@ -176,7 +178,7 @@
     else:
         if options.text:
             if isinstance(input, basestring):
-                input = open(input, 'r')
+                input = open(input, 'rb')
             else:
                 print(sys.argv[0], ': cannot do -t from stdin')
                 sys.exit(1)
diff --git a/Lib/xml/dom/pulldom.py b/Lib/xml/dom/pulldom.py
index c1463c91..c15618f 100644
--- a/Lib/xml/dom/pulldom.py
+++ b/Lib/xml/dom/pulldom.py
@@ -335,9 +335,9 @@
 
 def parseString(string, parser=None):
     try:
-        from cStringIO import StringIO
+        from io import StringIO
     except ImportError:
-        from StringIO import StringIO
+        from io import StringIO
 
     bufsize = len(string)
     buf = StringIO(string)
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index 2fba177..782af81 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -625,15 +625,16 @@
     # Writes the element tree to a file, as XML.
     #
     # @param file A file name, or a file object opened for writing.
-    # @param encoding Optional output encoding (default is US-ASCII).
+    # @param encoding Optional output encoding (default is None)
 
-    def write(self, file, encoding="us-ascii"):
+    def write(self, file, encoding=None):
         assert self._root is not None
         if not hasattr(file, "write"):
-            file = open(file, "wb")
-        if not encoding:
-            encoding = "us-ascii"
-        elif encoding != "utf-8" and encoding != "us-ascii":
+            if encoding:
+                file = open(file, "wb")
+            else:
+                file = open(file, "w")
+        if encoding and encoding != "utf-8":
             file.write(_encode("<?xml version='1.0' encoding='%s'?>\n" % encoding, encoding))
         self._write(file, self._root, encoding, {})
 
@@ -720,10 +721,10 @@
         sys.stdout.write("\n")
 
 def _encode(s, encoding):
-    try:
+    if encoding:
         return s.encode(encoding)
-    except AttributeError:
-        return s # 1.5.2: assume the string uses the right encoding
+    else:
+        return s
 
 _escape = re.compile(r"[&<>\"\u0080-\uffff]+")
 
@@ -954,10 +955,11 @@
 
 ##
 # Generates a string representation of an XML element, including all
-# subelements.
+# subelements.  If encoding is None, the return type is a string;
+# otherwise it is a bytes array.
 #
 # @param element An Element instance.
-# @return An encoded string containing the XML data.
+# @return An (optionally) encoded string containing the XML data.
 # @defreturn string
 
 def tostring(element, encoding=None):
@@ -967,7 +969,10 @@
     file = dummy()
     file.write = data.append
     ElementTree(element).write(file, encoding)
-    return b"".join(data)
+    if encoding:
+        return b"".join(data)
+    else:
+        return "".join(data)
 
 ##
 # Generic element structure builder.  This builder converts a sequence
diff --git a/Lib/xml/sax/__init__.py b/Lib/xml/sax/__init__.py
index 242c689..b161b1f 100644
--- a/Lib/xml/sax/__init__.py
+++ b/Lib/xml/sax/__init__.py
@@ -33,10 +33,7 @@
     parser.parse(source)
 
 def parseString(string, handler, errorHandler=ErrorHandler()):
-    try:
-        from cStringIO import StringIO
-    except ImportError:
-        from StringIO import StringIO
+    from io import BytesIO
 
     if errorHandler is None:
         errorHandler = ErrorHandler()
@@ -45,7 +42,7 @@
     parser.setErrorHandler(errorHandler)
 
     inpsrc = InputSource()
-    inpsrc.setByteStream(StringIO(string))
+    inpsrc.setByteStream(BytesIO(string))
     parser.parse(inpsrc)
 
 # this is the parser list used by the make_parser function if no
diff --git a/Misc/BeOS-setup.py b/Misc/BeOS-setup.py
index aeb8ae7..0d53d02 100644
--- a/Misc/BeOS-setup.py
+++ b/Misc/BeOS-setup.py
@@ -230,10 +230,6 @@
         # Fred Drake's interface to the Python parser
         exts.append( Extension('parser', ['parsermodule.c']) )
 
-        # cStringIO and cPickle
-        exts.append( Extension('cStringIO', ['cStringIO.c']) )
-        exts.append( Extension('cPickle', ['cPickle.c']) )
-
         # Memory-mapped files (also works on Win32).
         exts.append( Extension('mmap', ['mmapmodule.c']) )
 
diff --git a/Tools/framer/example.py b/Tools/framer/example.py
index 96f6278..8a267e9 100644
--- a/Tools/framer/example.py
+++ b/Tools/framer/example.py
@@ -14,7 +14,7 @@
 
     Usage:
 
-    from cStringIO import StringIO
+    from io import StringIO
 
     an_output_stream = StringIO()
     an_output_stream.write(some_stuff)
diff --git a/Tools/webchecker/webchecker.py b/Tools/webchecker/webchecker.py
index a172fd9..5b97851 100755
--- a/Tools/webchecker/webchecker.py
+++ b/Tools/webchecker/webchecker.py
@@ -109,7 +109,7 @@
 import sys
 import os
 from types import *
-import StringIO
+import io
 import getopt
 import pickle
 
@@ -721,12 +721,12 @@
         return infos
 
 
-class MyStringIO(StringIO.StringIO):
+class MyStringIO(io.StringIO):
 
     def __init__(self, url, info):
         self.__url = url
         self.__info = info
-        StringIO.StringIO.__init__(self)
+        super(MyStringIO, self).__init__(self)
 
     def info(self):
         return self.__info
diff --git a/setup.py b/setup.py
index aa8ee4e..9c8bd4b 100644
--- a/setup.py
+++ b/setup.py
@@ -460,9 +460,6 @@
         # Fred Drake's interface to the Python parser
         exts.append( Extension('parser', ['parsermodule.c']) )
 
-        # cStringIO
-        exts.append( Extension('cStringIO', ['cStringIO.c']) )
-
         # Memory-mapped files (also works on Win32).
         if platform not in ['atheos', 'mac']:
             exts.append( Extension('mmap', ['mmapmodule.c']) )