diff --git a/recipes/bloomberg_columns.recipe b/recipes/bloomberg_columns.recipe
index f43848d89d..552e3278d0 100644
--- a/recipes/bloomberg_columns.recipe
+++ b/recipes/bloomberg_columns.recipe
@@ -7,7 +7,7 @@ chron.com
 '''
 from datetime import datetime, timedelta
 from lxml import html, etree
-from StringIO import StringIO
+import io
 from calibre.web.feeds.recipes import BasicNewsRecipe
 import urllib2
 from collections import OrderedDict
@@ -31,7 +31,7 @@ def get_article_parsed(this_url):
     page = urllib2.urlopen(req)
     content = page.read()
     parser = etree.HTMLParser()
-    parsed = html.parse(StringIO(content), parser)
+    parsed = html.parse(io.BytesIO(bytes(content)), parser)
     return parsed
 
 
diff --git a/recipes/houston_chronicle.recipe b/recipes/houston_chronicle.recipe
index 8079974c0e..2a2ea05dc9 100644
--- a/recipes/houston_chronicle.recipe
+++ b/recipes/houston_chronicle.recipe
@@ -9,7 +9,7 @@ chron.com
 import re
 import time
 import urllib2
-from StringIO import StringIO
+import io
 from datetime import datetime
 import traceback
 import sys
@@ -66,7 +66,7 @@ def get_article_parsed(this_url):
     page = urllib2.urlopen(this_url)
     content = page.read()
     parser = etree.HTMLParser()
-    parsed = html.parse(StringIO(content), parser)
+    parsed = html.parse(io.BytesIO(bytes(content)), parser)
     return parsed
 
 
diff --git a/recipes/zeitde_sub.recipe b/recipes/zeitde_sub.recipe
index c396335e49..03905cbbb3 100644
--- a/recipes/zeitde_sub.recipe
+++ b/recipes/zeitde_sub.recipe
@@ -13,7 +13,7 @@ Die Zeit EPUB
 import os
 import zipfile
 import re
-import cStringIO
+import io
 from calibre.web.feeds.news import BasicNewsRecipe
 from calibre.ptempfile import PersistentTemporaryFile
 from calibre import walk
@@ -272,7 +272,7 @@ class ZeitEPUBAbo(BasicNewsRecipe):
             with closing(browser.open(cover_url)) as r:
                 cdata = r.read()
             from calibre.ebooks.metadata.pdf import get_metadata
-            stream = cStringIO.StringIO(cdata)
+            stream = io.BytesIO(cdata)
             cdata = None
             mi = get_metadata(stream)
             if mi.cover_data and mi.cover_data[1]:
diff --git a/src/calibre/devices/android/driver.py b/src/calibre/devices/android/driver.py
index fac9b100e0..c9ddbb22ed 100644
--- a/src/calibre/devices/android/driver.py
+++ b/src/calibre/devices/android/driver.py
@@ -4,10 +4,9 @@ __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
+import io
 import os
 
-import cStringIO
-
 from calibre import fsync
 from calibre.devices.usbms.driver import USBMS
 from polyglot.builtins import string_or_bytes
@@ -391,12 +390,12 @@ class WEBOS(USBMS):
 
         coverdata = getattr(metadata, 'thumbnail', None)
         if coverdata and coverdata[2]:
-            cover = Image.open(cStringIO.StringIO(coverdata[2]))
+            cover = Image.open(io.BytesIO(coverdata[2]))
         else:
             coverdata = lopen(I('library.png'), 'rb').read()
 
             cover = Image.new('RGB', (120,160), 'black')
-            im = Image.open(cStringIO.StringIO(coverdata))
+            im = Image.open(io.BytesIO(coverdata))
             im.thumbnail((120, 160), Image.ANTIALIAS)
 
             x, y = im.size
@@ -406,7 +405,7 @@ class WEBOS(USBMS):
             draw.text((1, 10), metadata.get('title', _('Unknown')).encode('ascii', 'ignore'))
             draw.text((1, 140), metadata.get('authors', _('Unknown'))[0].encode('ascii', 'ignore'))
 
-        data = cStringIO.StringIO()
+        data = io.BytesIO()
         cover.save(data, 'JPEG')
         coverdata = data.getvalue()
 
@@ -416,12 +415,12 @@ class WEBOS(USBMS):
 
         coverdata = getattr(metadata, 'thumbnail', None)
         if coverdata and coverdata[2]:
-            cover = Image.open(cStringIO.StringIO(coverdata[2]))
+            cover = Image.open(io.BytesIO(coverdata[2]))
         else:
             coverdata = lopen(I('library.png'), 'rb').read()
 
             cover = Image.new('RGB', (52,69), 'black')
-            im = Image.open(cStringIO.StringIO(coverdata))
+            im = Image.open(io.BytesIO(coverdata))
             im.thumbnail((52, 69), Image.ANTIALIAS)
 
             x, y = im.size
@@ -429,7 +428,7 @@ class WEBOS(USBMS):
 
         cover2 = cover.resize((52, 69), Image.ANTIALIAS).convert('RGB')
 
-        data = cStringIO.StringIO()
+        data = io.BytesIO()
         cover2.save(data, 'JPEG')
         coverdata = data.getvalue()
 
diff --git a/src/calibre/devices/cybook/t2b.py b/src/calibre/devices/cybook/t2b.py
index be99ca657c..c435cd5240 100644
--- a/src/calibre/devices/cybook/t2b.py
+++ b/src/calibre/devices/cybook/t2b.py
@@ -4,7 +4,7 @@ __copyright__ = '2009, John Schember <john at nachtimwald.com>'
 Write a t2b file to disk.
 '''
 
-import StringIO
+import io
 
 DEFAULT_T2B_DATA = 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 # noqa
 
@@ -31,7 +31,7 @@ def write_t2b(t2bfile, coverdata=None):
     '''
     from PIL import Image
     if coverdata is not None:
-        coverdata = StringIO.StringIO(coverdata)
+        coverdata = io.BytesIO(coverdata)
         cover = Image.open(coverdata).convert("L")
         cover.thumbnail((96, 144), Image.ANTIALIAS)
         t2bcover = Image.new('L', (96, 144), 'white')
@@ -49,4 +49,3 @@ def write_t2b(t2bfile, coverdata=None):
                 px = []
     else:
         t2bfile.write(DEFAULT_T2B_DATA)
-
diff --git a/src/calibre/devices/kindle/bookmark.py b/src/calibre/devices/kindle/bookmark.py
index 169a10654a..3d08483d17 100644
--- a/src/calibre/devices/kindle/bookmark.py
+++ b/src/calibre/devices/kindle/bookmark.py
@@ -5,7 +5,7 @@ __license__   = 'GPL v3'
 __docformat__ = 'restructuredtext en'
 
 import os
-from cStringIO import StringIO
+import io
 from struct import unpack
 
 
@@ -51,7 +51,7 @@ class Bookmark():  # {{{
         if self.bookmark_extension == 'mbp':
             MAGIC_MOBI_CONSTANT = 150
             with lopen(self.path,'rb') as f:
-                stream = StringIO(f.read())
+                stream = io.BytesIO(f.read())
                 data = StreamSlicer(stream)
                 self.timestamp, = unpack('>I', data[0x24:0x28])
                 bpar_offset, = unpack('>I', data[0x4e:0x52])
@@ -148,7 +148,7 @@ class Bookmark():  # {{{
                 # This will find the first instance of a clipping only
                 book_fs = self.path.replace('.%s' % self.bookmark_extension,'.%s' % self.book_format)
                 with lopen(book_fs,'rb') as f2:
-                    stream = StringIO(f2.read())
+                    stream = io.BytesIO(f2.read())
                     mi = get_topaz_metadata(stream)
                 my_clippings = self.path
                 split = my_clippings.find('documents') + len('documents/')
@@ -179,7 +179,7 @@ class Bookmark():  # {{{
             MAGIC_TOPAZ_CONSTANT = 33.33
             self.timestamp = os.path.getmtime(self.path)
             with lopen(self.path,'rb') as f:
-                stream = StringIO(f.read())
+                stream = io.BytesIO(f.read())
                 data = StreamSlicer(stream)
                 self.last_read = int(unpack('>I', data[5:9])[0])
                 self.last_read_location = self.last_read/MAGIC_TOPAZ_CONSTANT + 1
@@ -220,7 +220,7 @@ class Bookmark():  # {{{
         elif self.bookmark_extension == 'pdr':
             self.timestamp = os.path.getmtime(self.path)
             with lopen(self.path,'rb') as f:
-                stream = StringIO(f.read())
+                stream = io.BytesIO(f.read())
                 data = StreamSlicer(stream)
                 self.last_read = int(unpack('>I', data[5:9])[0])
                 entries, = unpack('>I', data[9:13])
@@ -289,7 +289,7 @@ class Bookmark():  # {{{
             # Read the book len from the header
             try:
                 with lopen(book_fs,'rb') as f:
-                    self.stream = StringIO(f.read())
+                    self.stream = io.BytesIO(f.read())
                     self.data = StreamSlicer(self.stream)
                     self.nrecs, = unpack('>H', self.data[76:78])
                     record0 = self.record(0)
diff --git a/src/calibre/devices/nook/driver.py b/src/calibre/devices/nook/driver.py
index 7268f6439e..22f7e779f4 100644
--- a/src/calibre/devices/nook/driver.py
+++ b/src/calibre/devices/nook/driver.py
@@ -8,9 +8,7 @@ __docformat__ = 'restructuredtext en'
 Device driver for Barns and Nobel's Nook
 '''
 
-import os, errno
-
-import cStringIO
+import io, os, errno
 
 from calibre import fsync, prints
 from calibre.constants import DEBUG
@@ -57,12 +55,12 @@ class NOOK(USBMS):
 
         coverdata = getattr(metadata, 'thumbnail', None)
         if coverdata and coverdata[2]:
-            cover = Image.open(cStringIO.StringIO(coverdata[2]))
+            cover = Image.open(io.BytesIO(coverdata[2]))
         else:
             coverdata = lopen(I('library.png'), 'rb').read()
 
             cover = Image.new('RGB', (96, 144), 'black')
-            im = Image.open(cStringIO.StringIO(coverdata))
+            im = Image.open(io.BytesIO(coverdata))
             im.thumbnail((96, 144), Image.ANTIALIAS)
 
             x, y = im.size
@@ -72,7 +70,7 @@ class NOOK(USBMS):
             draw.text((1, 15), metadata.get('title', _('Unknown')).encode('ascii', 'ignore'))
             draw.text((1, 115), metadata.get('authors', _('Unknown')).encode('ascii', 'ignore'))
 
-        data = cStringIO.StringIO()
+        data = io.BytesIO()
         cover.save(data, 'JPEG')
         coverdata = data.getvalue()
 
diff --git a/src/calibre/ebooks/chm/metadata.py b/src/calibre/ebooks/chm/metadata.py
index b35da416f1..5169765cfe 100644
--- a/src/calibre/ebooks/chm/metadata.py
+++ b/src/calibre/ebooks/chm/metadata.py
@@ -126,10 +126,10 @@ def _get_cover(soup, rdr):
                 ans = None
         if ans is not None:
             from PIL import Image
-            from cStringIO import StringIO
-            buf = StringIO()
+            import io
+            buf = io.BytesIO()
             try:
-                Image.open(StringIO(ans)).convert('RGB').save(buf, 'JPEG')
+                Image.open(io.BytesIO(ans)).convert('RGB').save(buf, 'JPEG')
                 ans = buf.getvalue()
             except:
                 ans = None
diff --git a/src/calibre/ebooks/compression/palmdoc.py b/src/calibre/ebooks/compression/palmdoc.py
index 5a8272ef9e..1027303133 100644
--- a/src/calibre/ebooks/compression/palmdoc.py
+++ b/src/calibre/ebooks/compression/palmdoc.py
@@ -5,7 +5,7 @@ from __future__ import print_function
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
 
-from cStringIO import StringIO
+import io
 from struct import pack
 
 from calibre.constants import plugins
@@ -50,7 +50,7 @@ def test():
 
 
 def py_compress_doc(data):
-    out = StringIO()
+    out = io.BytesIO()
     i = 0
     ldata = len(data)
     while i < ldata:
diff --git a/src/calibre/ebooks/conversion/plugins/htmlz_output.py b/src/calibre/ebooks/conversion/plugins/htmlz_output.py
index cdb74077ae..484dffa09e 100644
--- a/src/calibre/ebooks/conversion/plugins/htmlz_output.py
+++ b/src/calibre/ebooks/conversion/plugins/htmlz_output.py
@@ -6,9 +6,8 @@ __license__ = 'GPL 3'
 __copyright__ = '2011, John Schember <john@nachtimwald.com>'
 __docformat__ = 'restructuredtext en'
 
+import io
 import os
-from cStringIO import StringIO
-
 
 from calibre.customize.conversion import OutputFormatPlugin, \
     OptionRecommendation
@@ -127,7 +126,7 @@ class HTMLZOutput(OutputFormatPlugin):
 
             # Metadata
             with open(os.path.join(tdir, u'metadata.opf'), 'wb') as mdataf:
-                opf = OPF(StringIO(etree.tostring(oeb_book.metadata.to_opf1())))
+                opf = OPF(io.BytesIO(etree.tostring(oeb_book.metadata.to_opf1())))
                 mi = opf.to_book_metadata()
                 if cover_path:
                     mi.cover = u'cover.jpg'
diff --git a/src/calibre/ebooks/conversion/plugins/pml_output.py b/src/calibre/ebooks/conversion/plugins/pml_output.py
index 20bf1dc18d..4f09bbbee1 100644
--- a/src/calibre/ebooks/conversion/plugins/pml_output.py
+++ b/src/calibre/ebooks/conversion/plugins/pml_output.py
@@ -4,7 +4,7 @@ __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
 __docformat__ = 'restructuredtext en'
 
-import os, cStringIO
+import os, io
 
 from calibre.customize.conversion import (OutputFormatPlugin,
         OptionRecommendation)
@@ -65,12 +65,12 @@ class PMLOutput(OutputFormatPlugin):
         for item in manifest:
             if item.media_type in OEB_RASTER_IMAGES and item.href in image_hrefs.keys():
                 if opts.full_image_depth:
-                    im = Image.open(cStringIO.StringIO(item.data))
+                    im = Image.open(io.BytesIO(item.data))
                 else:
-                    im = Image.open(cStringIO.StringIO(item.data)).convert('P')
+                    im = Image.open(io.BytesIO(item.data)).convert('P')
                     im.thumbnail((300,300), Image.ANTIALIAS)
 
-                data = cStringIO.StringIO()
+                data = io.BytesIO()
                 im.save(data, 'PNG')
                 data = data.getvalue()
 
diff --git a/src/calibre/ebooks/conversion/plumber.py b/src/calibre/ebooks/conversion/plumber.py
index 3bfe919ea7..25ad577c8b 100644
--- a/src/calibre/ebooks/conversion/plumber.py
+++ b/src/calibre/ebooks/conversion/plumber.py
@@ -923,12 +923,12 @@ OptionRecommendation(name='search_replace',
     def download_cover(self, url):
         from calibre import browser
         from PIL import Image
-        from cStringIO import StringIO
+        import io
         from calibre.ptempfile import PersistentTemporaryFile
         self.log('Downloading cover from %r'%url)
         br = browser()
         raw = br.open_novisit(url).read()
-        buf = StringIO(raw)
+        buf = io.BytesIO(raw)
         pt = PersistentTemporaryFile('.jpg')
         pt.close()
         img = Image.open(buf)
diff --git a/src/calibre/ebooks/lit/reader.py b/src/calibre/ebooks/lit/reader.py
index ab060b8757..b487c673a1 100644
--- a/src/calibre/ebooks/lit/reader.py
+++ b/src/calibre/ebooks/lit/reader.py
@@ -8,9 +8,8 @@ __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net> ' \
     'and Marshall T. Vandegrift <llasram@gmail.com>'
 
-import struct, os, functools, re
+import io, struct, os, functools, re
 from urlparse import urldefrag
-from cStringIO import StringIO
 from urllib import unquote as urlunquote
 
 from lxml import etree
@@ -143,7 +142,7 @@ class UnBinary(object):
         self.is_html = map is HTML_MAP
         self.tag_atoms, self.attr_atoms = atoms
         self.dir = os.path.dirname(path)
-        buf = StringIO()
+        buf = io.BytesIO()
         self.binary_to_text(bin, buf)
         self.raw = buf.getvalue().lstrip()
         self.escape_reserved()
diff --git a/src/calibre/ebooks/lit/writer.py b/src/calibre/ebooks/lit/writer.py
index 35fe053902..0cadb1ac99 100644
--- a/src/calibre/ebooks/lit/writer.py
+++ b/src/calibre/ebooks/lit/writer.py
@@ -7,9 +7,9 @@ from __future__ import print_function
 __license__   = 'GPL v3'
 __copyright__ = '2008, Marshall T. Vandegrift <llasram@gmail.com>'
 
-from cStringIO import StringIO
 from struct import pack
 from itertools import izip, count, chain
+import io
 import time
 import random
 import re
@@ -151,7 +151,7 @@ class ReBinary(object):
         self.logger = oeb.logger
         self.manifest = oeb.manifest
         self.tags, self.tattrs = map
-        self.buf = StringIO()
+        self.buf = io.BytesIO()
         self.anchors = []
         self.page_breaks = []
         self.is_html  = is_html = map is HTML_MAP
@@ -282,7 +282,7 @@ class ReBinary(object):
         if len(self.anchors) > 6:
             self.logger.warn("More than six anchors in file %r. "
                 "Some links may not work properly." % self.item.href)
-        data = StringIO()
+        data = io.BytesIO()
         data.write(codepoint_to_chr(len(self.anchors)).encode('utf-8'))
         for anchor, offset in self.anchors:
             data.write(codepoint_to_chr(len(anchor)).encode('utf-8'))
@@ -333,7 +333,7 @@ class LitWriter(object):
         self._oeb = oeb
         self._logger = oeb.logger
         self._stream = stream
-        self._sections = [StringIO() for i in range(4)]
+        self._sections = [io.BytesIO() for i in range(4)]
         self._directory = []
         self._meta = None
         self._litize_oeb()
@@ -403,7 +403,7 @@ class LitWriter(object):
         piece2_offset = self._tell()
         self._write('IFCM', pack('<IIIQQ',
             1, CCHUNK_SIZE, 0x20000, ULL_NEG1, 1))
-        cchunk = StringIO()
+        cchunk = io.BytesIO()
         last = 0
         for i, dcount in izip(count(), dcounts):
             cchunk.write(decint(last))
@@ -505,7 +505,7 @@ class LitWriter(object):
                 manifest['css'].append(item)
             elif item.media_type in LIT_IMAGES:
                 manifest['images'].append(item)
-        data = StringIO()
+        data = io.BytesIO()
         data.write(pack('<Bc', 1, '\\'))
         offset = 0
         for state in states:
@@ -533,9 +533,9 @@ class LitWriter(object):
         self._add_file('/manifest', data.getvalue())
 
     def _build_page_breaks(self):
-        pb1 = StringIO()
-        pb2 = StringIO()
-        pb3 = StringIO()
+        pb1 = io.BytesIO()
+        pb2 = io.BytesIO()
+        pb3 = io.BytesIO()
         pb3cur = 0
         bits = 0
         linear = []
@@ -591,7 +591,7 @@ class LitWriter(object):
         self._add_file('/Version', pack('<HH', 8, 1))
 
     def _build_namelist(self):
-        data = StringIO()
+        data = io.BytesIO()
         data.write(pack('<HH', 0x3c, len(self._sections)))
         names = ['Uncompressed', 'MSCompressed', 'EbEncryptDS',
                  'EbEncryptOnlyDS']
@@ -628,7 +628,7 @@ class LitWriter(object):
                     unlen = len(data)
                     lzx = Compressor(17)
                     data, rtable = lzx.compress(data, flush=True)
-                    rdata = StringIO()
+                    rdata = io.BytesIO()
                     rdata.write(pack('<IIIIQQQQ',
                         3, len(rtable), 8, 0x28, unlen, len(data), 0x8000, 0))
                     for uncomp, comp in rtable[:-1]:
@@ -673,7 +673,7 @@ class LitWriter(object):
         directory.sort(cmp=lambda x, y:
             cmp(x.name.lower(), y.name.lower()))
         qrn = 1 + (1 << 2)
-        dchunk = StringIO()
+        dchunk = io.BytesIO()
         dcount = 0
         quickref = []
         name = directory[0].name
@@ -685,7 +685,7 @@ class LitWriter(object):
             usedlen = dchunk.tell() + len(next) + (len(quickref) * 2) + 52
             if usedlen >= DCHUNK_SIZE:
                 ddata.append((dchunk.getvalue(), quickref, dcount, name))
-                dchunk = StringIO()
+                dchunk = io.BytesIO()
                 dcount = 0
                 quickref = []
                 name = en
@@ -700,9 +700,9 @@ class LitWriter(object):
         dcounts = []
         ichunk = None
         if len(ddata) > 1:
-            ichunk = StringIO()
+            ichunk = io.BytesIO()
         for cid, (content, quickref, dcount, name) in izip(count(), ddata):
-            dchunk = StringIO()
+            dchunk = io.BytesIO()
             prev = cid - 1 if cid > 0 else ULL_NEG1
             next = cid + 1 if cid < cidmax else ULL_NEG1
             rem = DCHUNK_SIZE - (len(content) + 50)
diff --git a/src/calibre/ebooks/lrf/meta.py b/src/calibre/ebooks/lrf/meta.py
index 882762a78c..6a60e4c63d 100644
--- a/src/calibre/ebooks/lrf/meta.py
+++ b/src/calibre/ebooks/lrf/meta.py
@@ -13,9 +13,8 @@ to get and set meta information. For example:
 >>> lrf.category = "History"
 """
 
-import struct, zlib, sys, os
+import io, struct, zlib, sys, os
 from shutil import copyfileobj
-from cStringIO import StringIO
 import xml.dom.minidom as dom
 from functools import wraps
 
@@ -238,7 +237,7 @@ def insert_into_file(fileobj, data, start, end):
     @param end:     The position in fileobj of data that must not be overwritten
     @return:        C{start + len(data) - end}
     """
-    buffer = StringIO()
+    buffer = io.BytesIO()
     fileobj.seek(end)
     copyfileobj(fileobj, buffer, -1)
     buffer.flush()
diff --git a/src/calibre/ebooks/lrf/objects.py b/src/calibre/ebooks/lrf/objects.py
index 883ea82ccd..a6bd2c2322 100644
--- a/src/calibre/ebooks/lrf/objects.py
+++ b/src/calibre/ebooks/lrf/objects.py
@@ -1,7 +1,7 @@
 from __future__ import print_function
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
-import struct, array, zlib, cStringIO, collections, re
+import struct, array, zlib, io, collections, re
 
 from calibre.ebooks.lrf import LRFParseError, PRS500_PROFILE
 from calibre.constants import ispy3
@@ -98,7 +98,7 @@ class LRFContentObject(LRFObject):
     tag_map = {}
 
     def __init__(self, bytes, objects):
-        self.stream = bytes if hasattr(bytes, 'read') else cStringIO.StringIO(bytes)
+        self.stream = bytes if hasattr(bytes, 'read') else io.BytesIO(bytes)
         length = self.stream_size()
         self.objects = objects
         self._contents = []
@@ -601,7 +601,7 @@ class Block(LRFStream, TextCSS):
 
     def initialize(self):
         self.attrs = {}
-        stream = cStringIO.StringIO(self.stream)
+        stream = io.BytesIO(self.stream)
         tag = Tag(stream)
         if tag.id != 0xF503:
             raise LRFParseError("Bad block content")
@@ -836,7 +836,7 @@ class Text(LRFStream):
 
     def initialize(self):
         self.content = collections.deque()
-        stream = cStringIO.StringIO(self.stream)
+        stream = io.BytesIO(self.stream)
         length = len(self.stream)
         style = self.style.as_dict()
         current_style = style.copy()
@@ -1017,7 +1017,7 @@ class Canvas(LRFStream):
             if hasattr(self, attr):
                 self.attrs[attr] = getattr(self, attr)
         self._contents = []
-        stream = cStringIO.StringIO(self.stream)
+        stream = io.BytesIO(self.stream)
         while stream.tell() < len(self.stream):
             tag = Tag(stream)
             try:
@@ -1266,7 +1266,7 @@ class TocLabel(object):
 class TOCObject(LRFStream):
 
     def initialize(self):
-        stream = cStringIO.StringIO(self.stream)
+        stream = io.BytesIO(self.stream)
         c = struct.unpack("<H", stream.read(2))[0]
         stream.seek(4*(c+1))
         self._contents = []
diff --git a/src/calibre/ebooks/lrf/pylrs/pylrf.py b/src/calibre/ebooks/lrf/pylrs/pylrf.py
index 767494fefd..d8f8c42ddf 100644
--- a/src/calibre/ebooks/lrf/pylrs/pylrf.py
+++ b/src/calibre/ebooks/lrf/pylrs/pylrf.py
@@ -5,7 +5,7 @@
 """
 import struct
 import zlib
-import StringIO
+import io
 import codecs
 import os
 
@@ -473,7 +473,7 @@ class LrfTagStream(LrfStreamBase):
 
     def getStreamTags(self, encoding,
             optimizeTags=False, optimizeCompression=False):
-        stream = StringIO.StringIO()
+        stream = io.BytesIO()
         if optimizeTags:
             tagListOptimizer(self.tags)
 
@@ -587,7 +587,7 @@ class LrfToc(LrfObject):
         self.tags.extend(stream.getStreamTags())
 
     def _makeTocStream(self, toc, se):
-        stream = StringIO.StringIO()
+        stream = io.BytesIO()
         nEntries = len(toc)
 
         writeDWord(stream, nEntries)
@@ -770,4 +770,3 @@ class LrfWriter(object):
     def writeObjectTable(self, lrf):
         for tableEntry in self.objectTable:
             tableEntry.write(lrf)
-
diff --git a/src/calibre/ebooks/metadata/epub.py b/src/calibre/ebooks/metadata/epub.py
index ae0f672f17..dfbf875dc5 100644
--- a/src/calibre/ebooks/metadata/epub.py
+++ b/src/calibre/ebooks/metadata/epub.py
@@ -6,8 +6,7 @@ __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
 
 '''Read meta information from epub files'''
 
-import os, re, posixpath
-from cStringIO import StringIO
+import io, os, re, posixpath
 from contextlib import closing
 
 from calibre.utils.zipfile import ZipFile, BadZipfile, safe_replace
@@ -151,7 +150,7 @@ class OCFZipReader(OCFReader):
     def open(self, name, mode='r'):
         if isinstance(self.archive, LocalZipFile):
             return self.archive.open(name)
-        return StringIO(self.archive.read(name))
+        return io.BytesIO(self.archive.read(name))
 
     def read_bytes(self, name):
         return self.archive.read(name)
@@ -324,5 +323,3 @@ def set_metadata(stream, mi, apply_null=False, update_timestamp=False, force_ide
             os.remove(replacements[cpath].name)
     except:
         pass
-
-
diff --git a/src/calibre/ebooks/metadata/extz.py b/src/calibre/ebooks/metadata/extz.py
index 1d34bb0ad8..14d6588ce7 100644
--- a/src/calibre/ebooks/metadata/extz.py
+++ b/src/calibre/ebooks/metadata/extz.py
@@ -7,10 +7,9 @@ __copyright__ = '2011, John Schember <john@nachtimwald.com>'
 Read meta information from extZ (TXTZ, HTMLZ...) files.
 '''
 
+import io
 import os
 
-from cStringIO import StringIO
-
 from calibre.ebooks.metadata import MetaInformation
 from calibre.ebooks.metadata.opf2 import OPF
 from calibre.ptempfile import PersistentTemporaryFile
@@ -26,7 +25,7 @@ def get_metadata(stream, extract_cover=True):
     try:
         with ZipFile(stream) as zf:
             opf_name = get_first_opf_name(zf)
-            opf_stream = StringIO(zf.read(opf_name))
+            opf_stream = io.BytesIO(zf.read(opf_name))
             opf = OPF(opf_stream)
             mi = opf.to_book_metadata()
             if extract_cover:
@@ -53,7 +52,7 @@ def set_metadata(stream, mi):
     # Get the OPF in the archive.
     with ZipFile(stream) as zf:
         opf_path = get_first_opf_name(zf)
-        opf_stream = StringIO(zf.read(opf_path))
+        opf_stream = io.BytesIO(zf.read(opf_path))
     opf = OPF(opf_stream)
 
     # Cover.
@@ -77,7 +76,7 @@ def set_metadata(stream, mi):
 
     # Update the metadata.
     opf.smart_update(mi, replace_metadata=True)
-    newopf = StringIO(opf.render())
+    newopf = io.BytesIO(opf.render())
     safe_replace(stream, opf_path, newopf, extra_replacements=replacements, add_missing=True)
 
     # Cleanup temporary files.
diff --git a/src/calibre/ebooks/metadata/lit.py b/src/calibre/ebooks/metadata/lit.py
index 9f39fe594f..330bf8cc86 100644
--- a/src/calibre/ebooks/metadata/lit.py
+++ b/src/calibre/ebooks/metadata/lit.py
@@ -4,7 +4,7 @@ __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
 Support for reading the metadata from a LIT file.
 '''
 
-import cStringIO, os
+import io, os
 
 from calibre.ebooks.metadata.opf2 import OPF
 
@@ -15,7 +15,7 @@ def get_metadata(stream):
     litfile = LitContainer(stream, Log())
     src = litfile.get_metadata().encode('utf-8')
     litfile = litfile._litfile
-    opf = OPF(cStringIO.StringIO(src), os.getcwdu())
+    opf = OPF(io.BytesIO(src), os.getcwdu())
     mi = opf.to_book_metadata()
     covers = []
     for item in opf.iterguide():
@@ -39,4 +39,3 @@ def get_metadata(stream):
             idx = 1
     mi.cover_data = ('jpg', covers[idx][0])
     return mi
-
diff --git a/src/calibre/ebooks/metadata/odt.py b/src/calibre/ebooks/metadata/odt.py
index 1e6aa1e7fc..a216494d23 100644
--- a/src/calibre/ebooks/metadata/odt.py
+++ b/src/calibre/ebooks/metadata/odt.py
@@ -21,9 +21,8 @@
 #
 from __future__ import division
 
-import zipfile, re
+import zipfile, re, io
 import xml.sax.saxutils
-from cStringIO import StringIO
 
 from odf.namespaces import OFFICENS, DCNS, METANS
 from odf.opendocument import load as odLoad
@@ -168,7 +167,7 @@ def get_metadata(stream, extract_cover=True):
     parser.setFeature(xml.sax.handler.feature_external_ges, False)
     parser.setContentHandler(odfs)
     content = zin.read('meta.xml')
-    parser.parse(StringIO(content))
+    parser.parse(io.BytesIO(content))
     data = odfs.seenfields
     mi = MetaInformation(None, [])
     if 'title' in data:
diff --git a/src/calibre/ebooks/metadata/opf2.py b/src/calibre/ebooks/metadata/opf2.py
index b1b6688819..afff15e421 100644
--- a/src/calibre/ebooks/metadata/opf2.py
+++ b/src/calibre/ebooks/metadata/opf2.py
@@ -8,7 +8,7 @@ __docformat__ = 'restructuredtext en'
 lxml based OPF parser.
 '''
 
-import re, sys, unittest, functools, os, uuid, glob, cStringIO, json, copy
+import re, sys, unittest, functools, os, uuid, glob, io, json, copy
 from urllib import unquote
 from urlparse import urlparse
 
@@ -1723,7 +1723,6 @@ def metadata_to_opf(mi, as_string=True, default_lang=None):
 
 def test_m2o():
     from calibre.utils.date import now as nowf
-    from cStringIO import StringIO
     mi = MetaInformation('test & title', ['a"1', "a'2"])
     mi.title_sort = 'a\'"b'
     mi.author_sort = 'author sort'
@@ -1742,7 +1741,7 @@ def test_m2o():
     mi.cover = os.path.abspath('asd.jpg')
     opf = metadata_to_opf(mi)
     print(opf)
-    newmi = MetaInformation(OPF(StringIO(opf)))
+    newmi = MetaInformation(OPF(io.BytesIO(opf)))
     for attr in ('author_sort', 'title_sort', 'comments',
                     'publisher', 'series', 'series_index', 'rating',
                     'isbn', 'tags', 'cover_data', 'application_id',
@@ -1760,7 +1759,7 @@ def test_m2o():
 class OPFTest(unittest.TestCase):
 
     def setUp(self):
-        self.stream = cStringIO.StringIO(
+        self.stream = io.BytesIO(
 '''\
 <?xml version="1.0"  encoding="UTF-8"?>
 <package version="2.0" xmlns="http://www.idpf.org/2007/opf" >
@@ -1814,10 +1813,10 @@ class OPFTest(unittest.TestCase):
 
     def testCreator(self):
         opf = OPFCreator(os.getcwdu(), self.opf)
-        buf = cStringIO.StringIO()
+        buf = io.BytesIO()
         opf.render(buf)
         raw = buf.getvalue()
-        self.testReading(opf=OPF(cStringIO.StringIO(raw), os.getcwdu()))
+        self.testReading(opf=OPF(io.BytesIO(raw), os.getcwdu()))
 
     def testSmartUpdate(self):
         self.opf.smart_update(MetaInformation(self.opf))
@@ -1833,7 +1832,6 @@ def test():
 
 
 def test_user_metadata():
-    from cStringIO import StringIO
     mi = Metadata('Test title', ['test author1', 'test author2'])
     um = {
         '#myseries': {'#value#': u'test series\xe4', 'datatype':'text',
@@ -1846,12 +1844,12 @@ def test_user_metadata():
     mi.set_all_user_metadata(um)
     raw = metadata_to_opf(mi)
     opfc = OPFCreator(os.getcwdu(), other=mi)
-    out = StringIO()
+    out = io.BytesIO()
     opfc.render(out)
     raw2 = out.getvalue()
-    f = StringIO(raw)
+    f = io.BytesIO(raw)
     opf = OPF(f)
-    f2 = StringIO(raw2)
+    f2 = io.BytesIO(raw2)
     opf2 = OPF(f2)
     assert um == opf._user_metadata_
     assert um == opf2._user_metadata_
diff --git a/src/calibre/ebooks/metadata/snb.py b/src/calibre/ebooks/metadata/snb.py
index f6fdb2e2ab..d488c0de0b 100755
--- a/src/calibre/ebooks/metadata/snb.py
+++ b/src/calibre/ebooks/metadata/snb.py
@@ -6,7 +6,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2010, Li Fanxi <lifanxi@freemindworld.com>'
 
 import os
-from StringIO import StringIO
+import io
 from calibre.ebooks.metadata import MetaInformation
 from calibre.ebooks.snb.snbfile import SNBFile
 from lxml import etree
@@ -19,7 +19,7 @@ def get_metadata(stream, extract_cover=True):
 
     try:
         if not hasattr(stream, 'write'):
-            snbFile.Parse(StringIO(stream), True)
+            snbFile.Parse(io.BytesIO(stream), True)
         else:
             stream.seek(0)
             snbFile.Parse(stream, True)
diff --git a/src/calibre/ebooks/metadata/topaz.py b/src/calibre/ebooks/metadata/topaz.py
index f2c39a3464..a51822270f 100644
--- a/src/calibre/ebooks/metadata/topaz.py
+++ b/src/calibre/ebooks/metadata/topaz.py
@@ -5,7 +5,7 @@ __copyright__ = '2010, Greg Riker <griker@hotmail.com>'
 __docformat__ = 'restructuredtext en'
 
 ''' Read/write metadata from Amazon's topaz format '''
-import StringIO, sys, numbers
+import io, sys, numbers
 from struct import pack
 
 from calibre.ebooks.metadata import MetaInformation
@@ -194,7 +194,7 @@ class MetadataUpdater(object):
                 else:
                     return None
         dkey = self.topaz_headers[x]
-        dks = StringIO.StringIO()
+        dks = io.StringIO()
         dks.write(self.encode_vwi(len(dkey['tag'])))
         offset += 1
         dks.write(dkey['tag'])
@@ -290,7 +290,7 @@ class MetadataUpdater(object):
         delta = updated_md_len - original_md_len
 
         # Copy the first 5 bytes of the file: sig + num_recs
-        ths = StringIO.StringIO()
+        ths = io.StringIO()
         ths.write(self.data[:5])
 
         # Rewrite the offsets for hdr_offsets > metadata offset
@@ -377,9 +377,8 @@ if __name__ == '__main__':
         print(get_metadata(open(sys.argv[1], 'rb')))
     else:
         # Test set_metadata()
-        import cStringIO
         data = open(sys.argv[1], 'rb')
-        stream = cStringIO.StringIO()
+        stream = io.BytesIO()
         stream.write(data.read())
         mi = MetaInformation(title="Updated Title", authors=['Author, Random'])
         set_metadata(stream, mi)
diff --git a/src/calibre/ebooks/mobi/writer2/indexer.py b/src/calibre/ebooks/mobi/writer2/indexer.py
index 0353cf61b0..edb9abbe19 100644
--- a/src/calibre/ebooks/mobi/writer2/indexer.py
+++ b/src/calibre/ebooks/mobi/writer2/indexer.py
@@ -10,7 +10,7 @@ __docformat__ = 'restructuredtext en'
 
 import numbers
 from struct import pack
-from cStringIO import StringIO
+import io
 from collections import OrderedDict, defaultdict
 
 from calibre.ebooks.mobi.utils import (encint, encode_number_as_hex,
@@ -166,7 +166,7 @@ class IndexEntry(object):
 
     @property
     def bytestring(self):
-        buf = StringIO()
+        buf = io.BytesIO()
         if isinstance(self.index, numbers.Integral):
             buf.write(encode_number_as_hex(self.index))
         else:
@@ -294,7 +294,7 @@ class TBS(object):  # {{{
                 self.book_tbs(data, first)
 
     def periodical_tbs(self, data, first, depth_map):
-        buf = StringIO()
+        buf = io.BytesIO()
 
         has_section_start = (depth_map[1] and
                 set(depth_map[1]).intersection(set(data['starts'])))
@@ -496,7 +496,7 @@ class Indexer(object):  # {{{
 
     def create_index_record(self, secondary=False):  # {{{
         header_length = 192
-        buf = StringIO()
+        buf = io.BytesIO()
         indices = list(SecondaryIndexEntry.entries()) if secondary else self.indices
 
         # Write index entries
@@ -539,7 +539,7 @@ class Indexer(object):  # {{{
     # }}}
 
     def create_header(self, secondary=False):  # {{{
-        buf = StringIO()
+        buf = io.BytesIO()
         if secondary:
             tagx_block = TAGX().secondary
         else:
diff --git a/src/calibre/ebooks/mobi/writer2/main.py b/src/calibre/ebooks/mobi/writer2/main.py
index 6fd8739a4c..6d61d8ff1e 100644
--- a/src/calibre/ebooks/mobi/writer2/main.py
+++ b/src/calibre/ebooks/mobi/writer2/main.py
@@ -7,8 +7,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2011, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
-import random, time
-from cStringIO import StringIO
+import io, random, time
 from struct import pack
 
 from calibre.ebooks import normalize
@@ -130,7 +129,7 @@ class MobiWriter(object):
             pbreak = 0
             running = offset
 
-            buf = StringIO()
+            buf = io.BytesIO()
 
             while breaks and (breaks[0] - offset) < RECORD_SIZE:
                 pbreak = (breaks.pop(0) - running) >> 3
@@ -163,7 +162,7 @@ class MobiWriter(object):
                 write_page_breaks_after_item=self.write_page_breaks_after_item)
         text = self.serializer()
         self.text_length = len(text)
-        text = StringIO(text)
+        text = io.BytesIO(text)
         nrecords = 0
         records_size = 0
 
@@ -228,7 +227,7 @@ class MobiWriter(object):
         # EOF record
         self.records.append(b'\xE9\x8E\x0D\x0A')
 
-        record0 = StringIO()
+        record0 = io.BytesIO()
         # The MOBI Header
         record0.write(pack(b'>HHIHHHH',
             self.compression,  # compression type # compression type
diff --git a/src/calibre/ebooks/oeb/reader.py b/src/calibre/ebooks/oeb/reader.py
index 1d0f0a444e..727e0199b4 100644
--- a/src/calibre/ebooks/oeb/reader.py
+++ b/src/calibre/ebooks/oeb/reader.py
@@ -7,7 +7,7 @@ from __future__ import print_function
 __license__   = 'GPL v3'
 __copyright__ = '2008, Marshall T. Vandegrift <llasram@gmail.com>'
 
-import sys, os, uuid, copy, re, cStringIO
+import sys, os, uuid, copy, re, io
 from itertools import izip
 from urlparse import urldefrag, urlparse
 from urllib import unquote as urlunquote
@@ -138,7 +138,7 @@ class OEBReader(object):
     def _metadata_from_opf(self, opf):
         from calibre.ebooks.metadata.opf2 import OPF
         from calibre.ebooks.oeb.transforms.metadata import meta_info_to_oeb_metadata
-        stream = cStringIO.StringIO(etree.tostring(opf, xml_declaration=True, encoding='utf-8'))
+        stream = io.BytesIO(etree.tostring(opf, xml_declaration=True, encoding='utf-8'))
         o = OPF(stream)
         pwm = o.primary_writing_mode
         if pwm:
diff --git a/src/calibre/ebooks/pdb/ereader/writer.py b/src/calibre/ebooks/pdb/ereader/writer.py
index 77c6a0c80a..e1f6006dfe 100644
--- a/src/calibre/ebooks/pdb/ereader/writer.py
+++ b/src/calibre/ebooks/pdb/ereader/writer.py
@@ -8,6 +8,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
 __docformat__ = 'restructuredtext en'
 
+import io
 import re
 import struct
 import zlib
@@ -18,8 +19,6 @@ try:
 except ImportError:
     import Image
 
-import cStringIO
-
 from calibre.ebooks.pdb.formatwriter import FormatWriter
 from calibre.ebooks.pdb.header import PdbHeaderBuilder
 from calibre.ebooks.pml.pmlml import PMLMLizer
@@ -141,10 +140,10 @@ class Writer(FormatWriter):
         for item in manifest:
             if item.media_type in OEB_RASTER_IMAGES and item.href in image_hrefs.keys():
                 try:
-                    im = Image.open(cStringIO.StringIO(item.data)).convert('P')
+                    im = Image.open(io.BytesIO(item.data)).convert('P')
                     im.thumbnail((300,300), Image.ANTIALIAS)
 
-                    data = cStringIO.StringIO()
+                    data = io.BytesIO()
                     im.save(data, 'PNG')
                     data = data.getvalue()
 
diff --git a/src/calibre/ebooks/rb/writer.py b/src/calibre/ebooks/rb/writer.py
index ab46ca45a0..dc83476b39 100644
--- a/src/calibre/ebooks/rb/writer.py
+++ b/src/calibre/ebooks/rb/writer.py
@@ -4,6 +4,7 @@ __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
 __docformat__ = 'restructuredtext en'
 
+import io
 import struct
 import zlib
 
@@ -13,8 +14,6 @@ try:
 except ImportError:
     import Image
 
-import cStringIO
-
 from calibre.ebooks.rb.rbml import RBMLizer
 from calibre.ebooks.rb import HEADER
 from calibre.ebooks.rb import unique_name
@@ -121,8 +120,8 @@ class RBWriter(object):
                 try:
                     data = ''
 
-                    im = Image.open(cStringIO.StringIO(item.data)).convert('L')
-                    data = cStringIO.StringIO()
+                    im = Image.open(io.BytesIO(item.data)).convert('L')
+                    data = io.BytesIO()
                     im.save(data, 'PNG')
                     data = data.getvalue()
 
@@ -152,4 +151,3 @@ class RBWriter(object):
         text += 'BODY=index.html\n'
 
         return text
-
diff --git a/src/calibre/ebooks/rtf/rtfml.py b/src/calibre/ebooks/rtf/rtfml.py
index 92de7f0c2e..2e84cfbafc 100644
--- a/src/calibre/ebooks/rtf/rtfml.py
+++ b/src/calibre/ebooks/rtf/rtfml.py
@@ -10,7 +10,7 @@ Transform OEB content into RTF markup
 
 import os
 import re
-import cStringIO
+import io
 
 from lxml import etree
 
@@ -79,15 +79,15 @@ def txt2rtf(text):
     if not isinstance(text, unicode_type):
         return text
 
-    buf = cStringIO.StringIO()
+    buf = io.StringIO()
     for x in text:
         val = ord(x)
         if val == 160:
-            buf.write('\\~')
+            buf.write(u'\\~')
         elif val <= 127:
-            buf.write(x)
+            buf.write(unicode_type(x))
         else:
-            c = r'\u{0:d}?'.format(val)
+            c = unicode_type(r'\u{0:d}?'.format(val))
             buf.write(c)
     return buf.getvalue()
 
diff --git a/src/calibre/gui2/__init__.py b/src/calibre/gui2/__init__.py
index a6ea48b34d..17112f9dc5 100644
--- a/src/calibre/gui2/__init__.py
+++ b/src/calibre/gui2/__init__.py
@@ -1261,7 +1261,7 @@ def form_to_compiled_form(form):
 
 
 def build_forms(srcdir, info=None, summary=False, check_for_migration=False):
-    import re, cStringIO
+    import re, io
     from PyQt5.uic import compileUi
     forms = find_forms(srcdir)
     if info is None:
@@ -1286,7 +1286,7 @@ def build_forms(srcdir, info=None, summary=False, check_for_migration=False):
         if force_compile or not os.path.exists(compiled_form) or os.stat(form).st_mtime > os.stat(compiled_form).st_mtime:
             if not summary:
                 info('\tCompiling form', form)
-            buf = cStringIO.StringIO()
+            buf = io.BytesIO()
             compileUi(form, buf)
             dat = buf.getvalue()
             dat = dat.replace('import images_rc', '')
diff --git a/src/calibre/gui2/device.py b/src/calibre/gui2/device.py
index 7d5beb3359..456a0dea3b 100644
--- a/src/calibre/gui2/device.py
+++ b/src/calibre/gui2/device.py
@@ -3,7 +3,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
 
 # Imports {{{
-import os, traceback, Queue, time, cStringIO, re, sys, weakref
+import os, traceback, Queue, time, io, re, sys, weakref
 from threading import Thread, Event
 
 from PyQt5.Qt import (
@@ -113,7 +113,7 @@ class DeviceJob(BaseJob):  # {{{
 
     @property
     def log_file(self):
-        return cStringIO.StringIO(self._details.encode('utf-8'))
+        return io.BytesIO(self._details.encode('utf-8'))
 
     # }}}
 
diff --git a/src/calibre/gui2/dialogs/catalog.py b/src/calibre/gui2/dialogs/catalog.py
index 0537b35473..1f32406b76 100644
--- a/src/calibre/gui2/dialogs/catalog.py
+++ b/src/calibre/gui2/dialogs/catalog.py
@@ -22,7 +22,7 @@ class Catalog(QDialog, Ui_Dialog):
     ''' Catalog Dialog builder'''
 
     def __init__(self, parent, dbspec, ids, db):
-        import re, cStringIO
+        import re, io
         from calibre import prints as info
         from PyQt5.uic import compileUi
 
@@ -68,7 +68,7 @@ class Catalog(QDialog, Ui_Dialog):
                     # Compile the .ui form provided in plugin.zip
                     if not os.path.exists(compiled_form):
                         # info('\tCompiling form', form)
-                        buf = cStringIO.StringIO()
+                        buf = io.BytesIO()
                         compileUi(form, buf)
                         dat = buf.getvalue()
                         dat = re.compile(r'QtGui.QApplication.translate\(.+?,\s+"(.+?)(?<!\\)",.+?\)',
diff --git a/src/calibre/translations/dynamic.py b/src/calibre/translations/dynamic.py
index ff50a6609b..2db1c52815 100644
--- a/src/calibre/translations/dynamic.py
+++ b/src/calibre/translations/dynamic.py
@@ -5,7 +5,7 @@ Dynamic language lookup of translations for user-visible strings.
 __license__   = 'GPL v3'
 __copyright__ = '2008, Marshall T. Vandegrift <llasram@gmail.com>'
 
-import cStringIO
+import io
 from gettext import GNUTranslations
 from calibre.utils.localization import get_lc_messages_path
 from zipfile import ZipFile
@@ -25,7 +25,7 @@ def translate(lang, text):
             with ZipFile(P('localization/locales.zip',
                 allow_user_override=False), 'r') as zf:
                 try:
-                    buf = cStringIO.StringIO(zf.read(mpath + '/messages.mo'))
+                    buf = io.BytesIO(zf.read(mpath + '/messages.mo'))
                 except:
                     pass
                 else:
diff --git a/src/calibre/utils/ipc/job.py b/src/calibre/utils/ipc/job.py
index 34a2a24d20..73829f83bb 100644
--- a/src/calibre/utils/ipc/job.py
+++ b/src/calibre/utils/ipc/job.py
@@ -8,7 +8,7 @@ __docformat__ = 'restructuredtext en'
 
 _count = 0
 
-import time, cStringIO
+import time, io
 from Queue import Queue, Empty
 
 from calibre import prints
@@ -146,7 +146,7 @@ class BaseJob(object):
     def log_file(self):
         if self.log_path:
             return open(self.log_path, 'rb')
-        return cStringIO.StringIO(_('No details available.').encode('utf-8',
+        return io.BytesIO(_('No details available.').encode('utf-8',
             'replace'))
 
     @property
@@ -159,6 +159,3 @@ class ParallelJob(BaseJob):
     def __init__(self, name, description, done, args=[], kwargs={}):
         self.name, self.args, self.kwargs = name, args, kwargs
         BaseJob.__init__(self, description, done)
-
-
-
diff --git a/src/calibre/utils/localization.py b/src/calibre/utils/localization.py
index 9da64132e0..7f42282a47 100644
--- a/src/calibre/utils/localization.py
+++ b/src/calibre/utils/localization.py
@@ -6,7 +6,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
-import os, locale, re, cStringIO
+import os, locale, re, io
 from gettext import GNUTranslations, NullTranslations
 
 from polyglot.builtins import unicode_type
@@ -129,14 +129,14 @@ def get_all_translators():
         for lang in available_translations():
             mpath = get_lc_messages_path(lang)
             if mpath is not None:
-                buf = cStringIO.StringIO(zf.read(mpath + '/messages.mo'))
+                buf = io.BytesIO(zf.read(mpath + '/messages.mo'))
                 yield lang, GNUTranslations(buf)
 
 
 def get_single_translator(mpath, which='messages'):
     from zipfile import ZipFile
     with ZipFile(P('localization/locales.zip', allow_user_override=False), 'r') as zf:
-        buf = cStringIO.StringIO(zf.read(mpath + '/%s.mo' % which))
+        buf = io.BytesIO(zf.read(mpath + '/%s.mo' % which))
         return GNUTranslations(buf)
 
 
@@ -185,14 +185,14 @@ lcdata = {
 
 def load_po(path):
     from calibre.translations.msgfmt import make
-    buf = cStringIO.StringIO()
+    buf = io.BytesIO()
     try:
         make(path, buf)
     except Exception:
         print (('Failed to compile translations file: %s, ignoring') % path)
         buf = None
     else:
-        buf = cStringIO.StringIO(buf.getvalue())
+        buf = io.BytesIO(buf.getvalue())
     return buf
 
 
@@ -216,12 +216,12 @@ def set_translators():
             with ZipFile(P('localization/locales.zip',
                 allow_user_override=False), 'r') as zf:
                 if buf is None:
-                    buf = cStringIO.StringIO(zf.read(mpath + '/messages.mo'))
+                    buf = io.BytesIO(zf.read(mpath + '/messages.mo'))
                 if mpath == 'nds':
                     mpath = 'de'
                 isof = mpath + '/iso639.mo'
                 try:
-                    iso639 = cStringIO.StringIO(zf.read(isof))
+                    iso639 = io.BytesIO(zf.read(isof))
                 except:
                     pass  # No iso639 translations for this lang
                 if buf is not None:
diff --git a/src/calibre/utils/zipfile.py b/src/calibre/utils/zipfile.py
index 9699543d9b..0ff4727de6 100644
--- a/src/calibre/utils/zipfile.py
+++ b/src/calibre/utils/zipfile.py
@@ -4,7 +4,7 @@ a zip archive, detecting filename encoding, updating zip files, etc.
 """
 from __future__ import print_function
 import struct, os, time, sys, shutil, stat, re, io
-import binascii, cStringIO
+import binascii
 from contextlib import closing
 from tempfile import SpooledTemporaryFile
 
@@ -835,7 +835,7 @@ class ZipFile:
         self.start_dir = offset_cd + concat
         fp.seek(self.start_dir, 0)
         data = fp.read(size_cd)
-        fp = cStringIO.StringIO(data)
+        fp = io.BytesIO(data)
         total = 0
         while total < size_cd:
             centdir = fp.read(sizeCentralDir)
diff --git a/src/calibre/web/feeds/news.py b/src/calibre/web/feeds/news.py
index 9a2e616867..9ca3aae8c7 100644
--- a/src/calibre/web/feeds/news.py
+++ b/src/calibre/web/feeds/news.py
@@ -7,7 +7,7 @@ Defines various abstract base classes that can be subclassed to create powerful
 __docformat__ = "restructuredtext en"
 
 
-import os, time, traceback, re, urlparse, sys, cStringIO
+import os, time, traceback, re, urlparse, sys, io
 from collections import defaultdict
 from functools import partial
 from contextlib import nested, closing
@@ -1305,7 +1305,7 @@ class BasicNewsRecipe(Recipe):
             ext = cu.split('/')[-1].rpartition('.')[-1].lower().strip()
             if ext == 'pdf':
                 from calibre.ebooks.metadata.pdf import get_metadata
-                stream = cStringIO.StringIO(cdata)
+                stream = io.BytesIO(cdata)
                 cdata = None
                 mi = get_metadata(stream)
                 if mi.cover_data and mi.cover_data[1]:
@@ -1807,7 +1807,7 @@ class CalibrePeriodical(BasicNewsRecipe):
                         ' Either your subscription has expired or you have'
                         ' exceeded the maximum allowed downloads for today.'))
             raise
-        f = cStringIO.StringIO(raw)
+        f = io.BytesIO(raw)
         from calibre.utils.zipfile import ZipFile
         zf = ZipFile(f)
         zf.extractall()