From c1fb63378ffcaeb083ebef830349070cbca683e3 Mon Sep 17 00:00:00 2001
From: Eli Schwartz <eschwartz@archlinux.org>
Date: Mon, 11 Mar 2019 14:37:02 -0400
Subject: [PATCH] python3: migrate lots of code to io.(Bytes|String)IO instead
 of c?StringIO

This is the only IO representation on python3, and it is backported to
python2 to aid in porting but requires determining whether to handle
bytes or unicode...  which is sort of the point of porting, so let's
handle this properly everywhere we can.
---
 recipes/bloomberg_columns.recipe              |  4 +--
 recipes/houston_chronicle.recipe              |  4 +--
 recipes/zeitde_sub.recipe                     |  4 +--
 src/calibre/devices/android/driver.py         | 15 +++++-----
 src/calibre/devices/cybook/t2b.py             |  5 ++--
 src/calibre/devices/kindle/bookmark.py        | 12 ++++----
 src/calibre/devices/nook/driver.py            | 10 +++----
 src/calibre/ebooks/chm/metadata.py            |  6 ++--
 src/calibre/ebooks/compression/palmdoc.py     |  4 +--
 .../ebooks/conversion/plugins/htmlz_output.py |  5 ++--
 .../ebooks/conversion/plugins/pml_output.py   |  8 ++---
 src/calibre/ebooks/conversion/plumber.py      |  4 +--
 src/calibre/ebooks/lit/reader.py              |  5 ++--
 src/calibre/ebooks/lit/writer.py              | 30 +++++++++----------
 src/calibre/ebooks/lrf/meta.py                |  5 ++--
 src/calibre/ebooks/lrf/objects.py             | 12 ++++----
 src/calibre/ebooks/lrf/pylrs/pylrf.py         |  7 ++---
 src/calibre/ebooks/metadata/epub.py           |  7 ++---
 src/calibre/ebooks/metadata/extz.py           |  9 +++---
 src/calibre/ebooks/metadata/lit.py            |  5 ++--
 src/calibre/ebooks/metadata/odt.py            |  5 ++--
 src/calibre/ebooks/metadata/opf2.py           | 18 +++++------
 src/calibre/ebooks/metadata/snb.py            |  4 +--
 src/calibre/ebooks/metadata/topaz.py          |  9 +++---
 src/calibre/ebooks/mobi/writer2/indexer.py    | 10 +++----
 src/calibre/ebooks/mobi/writer2/main.py       |  9 +++---
 src/calibre/ebooks/oeb/reader.py              |  4 +--
 src/calibre/ebooks/pdb/ereader/writer.py      |  7 ++---
 src/calibre/ebooks/rb/writer.py               |  8 ++---
 src/calibre/ebooks/rtf/rtfml.py               | 10 +++----
 src/calibre/gui2/__init__.py                  |  4 +--
 src/calibre/gui2/device.py                    |  4 +--
 src/calibre/gui2/dialogs/catalog.py           |  4 +--
 src/calibre/translations/dynamic.py           |  4 +--
 src/calibre/utils/ipc/job.py                  |  7 ++---
 src/calibre/utils/localization.py             | 14 ++++-----
 src/calibre/utils/zipfile.py                  |  4 +--
 src/calibre/web/feeds/news.py                 |  6 ++--
 38 files changed, 134 insertions(+), 158 deletions(-)

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()