diff --git a/src/calibre/ebooks/oeb/polish/cascade.py b/src/calibre/ebooks/oeb/polish/cascade.py
index 39797af130..ebc1a60bf4 100644
--- a/src/calibre/ebooks/oeb/polish/cascade.py
+++ b/src/calibre/ebooks/oeb/polish/cascade.py
@@ -165,7 +165,7 @@ def resolve_styles(container, name, select=None, sheet_callback=None):
     style_map = defaultdict(list)
     pseudo_style_map = defaultdict(list)
     rule_index_counter = count()
-    pseudo_pat = re.compile(u':{1,2}(%s)' % ('|'.join(INAPPROPRIATE_PSEUDO_CLASSES)), re.I)
+    pseudo_pat = re.compile(':{1,2}(%s)' % ('|'.join(INAPPROPRIATE_PSEUDO_CLASSES)), re.I)
 
     def process_sheet(sheet, sheet_name):
         if sheet_callback is not None:
diff --git a/src/calibre/ebooks/oeb/polish/container.py b/src/calibre/ebooks/oeb/polish/container.py
index 69beea9393..56a2bde352 100644
--- a/src/calibre/ebooks/oeb/polish/container.py
+++ b/src/calibre/ebooks/oeb/polish/container.py
@@ -1277,7 +1277,7 @@ class EpubContainer(Container):
                     break
         if raw_unique_identifier is not None:
             idpf_key = raw_unique_identifier
-            idpf_key = re.sub(u'[\u0020\u0009\u000d\u000a]', u'', idpf_key)
+            idpf_key = re.sub('[\u0020\u0009\u000d\u000a]', '', idpf_key)
             idpf_key = hashlib.sha1(idpf_key.encode('utf-8')).digest()
         key = None
         for item in self.opf_xpath('//*[local-name()="metadata"]/*'
diff --git a/src/calibre/gui2/library/models.py b/src/calibre/gui2/library/models.py
index 05f816f194..95240d4d11 100644
--- a/src/calibre/gui2/library/models.py
+++ b/src/calibre/gui2/library/models.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -37,7 +38,7 @@ Counts = namedtuple('Counts', 'library_total total current')
 
 def human_readable(size, precision=1):
     """ Convert a size in bytes into megabytes """
-    return ('%.'+str(precision)+'f') % ((size/(1024.*1024.)),)
+    return ('%.'+unicode_type(precision)+'f') % (size/(1024*1024))
 
 
 TIME_FMT = '%d %b %Y'
@@ -71,7 +72,7 @@ class ColumnColor(object):  # {{{
         self.formatter = formatter
 
     def __call__(self, id_, key, fmt, db, color_cache, template_cache):
-        key += str(hash(fmt))
+        key += unicode_type(hash(fmt))
         if id_ in color_cache and key in color_cache[id_]:
             self.mi = None
             color = color_cache[id_][key]
@@ -112,7 +113,7 @@ class ColumnIcon(object):  # {{{
             icons = []
             for dex, (kind, fmt) in enumerate(fmts):
                 rule_icons = self.formatter.safe_format(fmt, self.mi, '', self.mi,
-                                    column_name=cache_index+str(dex),
+                                    column_name=cache_index+unicode_type(dex),
                                     template_cache=template_cache)
                 if not rule_icons:
                     continue
@@ -774,14 +775,14 @@ class BooksModel(QAbstractTableModel):  # {{{
                         return None if bt else bn
                     return by if val else bn
             elif field == 'size':
-                sz_mult = 1.0/(1024**2)
+                sz_mult = 1/(1024**2)
 
                 def func(idx):
                     val = fffunc(field_obj, idfunc(idx), default_value=0) or 0
                     if val == 0:
                         return None
-                    ans = u'%.1f' % (val * sz_mult)
-                    return (u'<0.1' if ans == u'0.0' else ans)
+                    ans = '%.1f' % (val * sz_mult)
+                    return ('<0.1' if ans == '0.0' else ans)
             elif field == 'languages':
                 def func(idx):
                     return (', '.join(calibre_langcode_to_name(x) for x in fffunc(field_obj, idfunc(idx))))
@@ -874,7 +875,7 @@ class BooksModel(QAbstractTableModel):  # {{{
         def stars_tooltip(func, allow_half=True):
             def f(idx):
                 ans = val = int(func(idx))
-                ans = str(val // 2)
+                ans = unicode_type(val // 2)
                 if allow_half and val % 2:
                     ans += '.5'
                 return _('%s stars') % ans
@@ -1152,7 +1153,7 @@ class BooksModel(QAbstractTableModel):  # {{{
                 return False
             val = (int(value) if column == 'rating' else
                     value if column in ('timestamp', 'pubdate')
-                    else re.sub(u'\\s', u' ', unicode_type(value or '').strip()))
+                    else re.sub('\\s', ' ', unicode_type(value or '').strip()))
             id = self.db.id(row)
             books_to_refresh = {id}
             if column == 'rating':
diff --git a/src/calibre/gui2/library/views.py b/src/calibre/gui2/library/views.py
index 5eaa3975e7..3e9ed950c6 100644
--- a/src/calibre/gui2/library/views.py
+++ b/src/calibre/gui2/library/views.py
@@ -1,14 +1,13 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
-from __future__ import print_function
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
 import itertools, operator
 from functools import partial
-from polyglot.builtins import iteritems, map, unicode_type, range
 from collections import OrderedDict
 
 from PyQt5.Qt import (
@@ -31,6 +30,7 @@ from calibre.gui2.library import DEFAULT_SORT
 from calibre.constants import filesystem_encoding
 from calibre import force_unicode
 from calibre.utils.icu import primary_sort_key
+from polyglot.builtins import iteritems, map, range, unicode_type
 
 
 def restrict_column_width(self, col, old_size, new_size):
diff --git a/src/calibre/gui2/lrf_renderer/__init__.py b/src/calibre/gui2/lrf_renderer/__init__.py
index 7b0d098045..bffa3c0e04 100644
--- a/src/calibre/gui2/lrf_renderer/__init__.py
+++ b/src/calibre/gui2/lrf_renderer/__init__.py
@@ -1,4 +1,4 @@
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
-
-
diff --git a/src/calibre/gui2/lrf_renderer/bookview.py b/src/calibre/gui2/lrf_renderer/bookview.py
index c826004fef..9fdbbda97d 100644
--- a/src/calibre/gui2/lrf_renderer/bookview.py
+++ b/src/calibre/gui2/lrf_renderer/bookview.py
@@ -1,3 +1,5 @@
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
 
@@ -20,5 +22,3 @@ class BookView(QGraphicsView):
 
     def resize_for(self, width, height):
         self.preferred_size = QSize(width, height)
-
-
diff --git a/src/calibre/gui2/lrf_renderer/document.py b/src/calibre/gui2/lrf_renderer/document.py
index 644f4d9e17..4719d688de 100644
--- a/src/calibre/gui2/lrf_renderer/document.py
+++ b/src/calibre/gui2/lrf_renderer/document.py
@@ -1,6 +1,8 @@
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
+
 import collections, itertools, glob
 
 from PyQt5.Qt import (
@@ -8,10 +10,9 @@ from PyQt5.Qt import (
     QBrush, QColor, QFontDatabase, QGraphicsItem, QGraphicsLineItem)
 
 from calibre.gui2.lrf_renderer.text import TextBlock, FontLoader, COLOR, PixmapItem
-
-
 from calibre.ebooks.lrf.objects import RuledLine as _RuledLine
 from calibre.ebooks.lrf.objects import Canvas as __Canvas
+from polyglot.builtins import unicode_type
 
 
 class Color(QColor):
@@ -417,7 +418,7 @@ class Document(QGraphicsScene):
             fdata = QByteArray(lrf.font_map[font].data)
             id = QFontDatabase.addApplicationFontFromData(fdata)
             if id != -1:
-                font_map[font] = [str(i) for i in QFontDatabase.applicationFontFamilies(id)][0]
+                font_map[font] = [unicode_type(i) for i in QFontDatabase.applicationFontFamilies(id)][0]
 
         if load_substitutions:
             base = P('fonts/liberation/*.ttf')
diff --git a/src/calibre/gui2/lrf_renderer/main.py b/src/calibre/gui2/lrf_renderer/main.py
index 56d6287601..925fc08579 100644
--- a/src/calibre/gui2/lrf_renderer/main.py
+++ b/src/calibre/gui2/lrf_renderer/main.py
@@ -1,6 +1,8 @@
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
+
 import sys, logging, os, traceback, time
 
 from PyQt5.Qt import (
@@ -199,9 +201,9 @@ class Main(MainWindow, Ui_MainWindow):
             print('Error rendering document', file=sys.stderr)
             print(exception, file=sys.stderr)
             print(self.renderer.formatted_traceback, file=sys.stderr)
-            msg =  u'<p><b>%s</b>: '%(exception.__class__.__name__,) + as_unicode(exception) + u'</p>'
-            msg += u'<p>Failed to render document</p>'
-            msg += u'<p>Detailed <b>traceback</b>:<pre>'
+            msg =  '<p><b>%s</b>: '%(exception.__class__.__name__,) + as_unicode(exception) + '</p>'
+            msg += '<p>Failed to render document</p>'
+            msg += '<p>Detailed <b>traceback</b>:<pre>'
             msg += self.renderer.formatted_traceback + '</pre>'
             d = ConversionErrorDialog(self, 'Error while rendering file', msg)
             d.exec_()
diff --git a/src/calibre/gui2/lrf_renderer/text.py b/src/calibre/gui2/lrf_renderer/text.py
index 9231a17325..7014c1be1f 100644
--- a/src/calibre/gui2/lrf_renderer/text.py
+++ b/src/calibre/gui2/lrf_renderer/text.py
@@ -1,6 +1,8 @@
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
+
 import sys, collections, operator, copy, re, numbers
 
 from PyQt5.Qt import (
@@ -11,7 +13,7 @@ from calibre.ebooks.lrf.fonts import LIBERATION_FONT_MAP
 from calibre.ebooks.hyphenate import hyphenate_word
 from polyglot.builtins import unicode_type, string_or_bytes
 
-WEIGHT_MAP = lambda wt : int((wt/10.)-1)
+WEIGHT_MAP = lambda wt : int((wt/10)-1)
 NULL       = lambda a, b: a
 COLOR      = lambda a, b: QColor(*a)
 WEIGHT     = lambda a, b: WEIGHT_MAP(a)
@@ -41,7 +43,7 @@ class Plot(PixmapItem):
 
     def __init__(self, plot, dpi):
         img = plot.refobj
-        xsize, ysize = dpi*plot.attrs['xsize']/720., dpi*plot.attrs['ysize']/720.
+        xsize, ysize = dpi*plot.attrs['xsize']/720, dpi*plot.attrs['ysize']/720
         x0, y0, x1, y1 = img.x0, img.y0, img.x1, img.y1
         data, encoding = img.data, img.encoding
         PixmapItem.__init__(self, data, encoding, x0, y0, x1, y1, xsize, ysize)
@@ -95,7 +97,7 @@ class Style(object):
     map = collections.defaultdict(lambda : NULL)
 
     def __init__(self, style, dpi):
-        self.fdpi = dpi/720.
+        self.fdpi = dpi/720
         self.update(style.as_dict())
 
     def update(self, *args, **kwds):
@@ -154,7 +156,7 @@ class ParSkip(object):
         self.height = parskip
 
     def __str__(self):
-        return 'Parskip: '+str(self.height)
+        return 'Parskip: '+unicode_type(self.height)
 
 
 class TextBlock(object):
@@ -289,7 +291,7 @@ class TextBlock(object):
                                                       self.current_style.linespace,
                                                       self.opts.visual_debug)
             if self.height > self.max_y+10:
-                raise TextBlock.HeightExceeded(str(self.current_line))
+                raise TextBlock.HeightExceeded(unicode_type(self.current_line))
             self.lines.append(self.current_line)
             self.current_line = None
 
@@ -307,7 +309,7 @@ class TextBlock(object):
 
     def process_text(self, raw):
         for ent, rep in TextBlock.XML_ENTITIES.items():
-            raw = raw.replace(u'&%s;'%ent, rep)
+            raw = raw.replace('&%s;'%ent, rep)
         while len(raw) > 0:
             if self.current_line is None:
                 self.create_line()
@@ -325,7 +327,7 @@ class TextBlock(object):
     def __str__(self):
         s = ''
         for line in self:
-            s += str(line) + '\n'
+            s += unicode_type(line) + '\n'
         return s
 
 
@@ -563,7 +565,7 @@ class Line(QGraphicsItem):
             return (textwidth-self.width)/2.
 
     def __unicode__(self):
-        s = u''
+        s = ''
         for tok in self.tokens:
             if isinstance(tok, numbers.Number):
                 s += ' '
diff --git a/src/calibre/gui2/metadata/__init__.py b/src/calibre/gui2/metadata/__init__.py
index 31be9f7fc6..0f9dc4e7f8 100644
--- a/src/calibre/gui2/metadata/__init__.py
+++ b/src/calibre/gui2/metadata/__init__.py
@@ -1,9 +1,7 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2011, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
-
-
-
diff --git a/src/calibre/gui2/metadata/basic_widgets.py b/src/calibre/gui2/metadata/basic_widgets.py
index 3e8aa4526d..68a5ea928f 100644
--- a/src/calibre/gui2/metadata/basic_widgets.py
+++ b/src/calibre/gui2/metadata/basic_widgets.py
@@ -1175,7 +1175,7 @@ class Cover(ImageView):  # {{{
             except IOError as e:
                 d = error_dialog(
                         self, _('Error reading file'),
-                        _("<p>There was an error reading from file: <br /><b>") + _file + "</b></p><br />"+str(e))
+                        _("<p>There was an error reading from file: <br /><b>") + _file + "</b></p><br />"+unicode_type(e))
                 d.exec_()
             if cover:
                 orig = self.current_val
diff --git a/src/calibre/gui2/metadata/pdf_covers.py b/src/calibre/gui2/metadata/pdf_covers.py
index f2a660bdb2..370fa5a32c 100644
--- a/src/calibre/gui2/metadata/pdf_covers.py
+++ b/src/calibre/gui2/metadata/pdf_covers.py
@@ -99,7 +99,7 @@ class PDFCovers(QDialog):
             pass
 
     def render(self):
-        self.current_tdir = os.path.join(self.tdir, str(self.first))
+        self.current_tdir = os.path.join(self.tdir, unicode_type(self.first))
         self.error = None
         try:
             os.mkdir(self.current_tdir)
diff --git a/src/calibre/gui2/preferences/__init__.py b/src/calibre/gui2/preferences/__init__.py
index 304043d4ef..746e1d67eb 100644
--- a/src/calibre/gui2/preferences/__init__.py
+++ b/src/calibre/gui2/preferences/__init__.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -214,7 +215,7 @@ class CommaSeparatedList(Setting):
     def set_gui_val(self, val):
         x = ''
         if val:
-            x = u', '.join(val)
+            x = ', '.join(val)
         self.gui_obj.setText(x)
 
     def get_gui_val(self):
diff --git a/src/calibre/gui2/preferences/adding.py b/src/calibre/gui2/preferences/adding.py
index d2ae8f547f..90bb9a74c3 100644
--- a/src/calibre/gui2/preferences/adding.py
+++ b/src/calibre/gui2/preferences/adding.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/behavior.py b/src/calibre/gui2/preferences/behavior.py
index 8de1b43682..d390d7a216 100644
--- a/src/calibre/gui2/preferences/behavior.py
+++ b/src/calibre/gui2/preferences/behavior.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/columns.py b/src/calibre/gui2/preferences/columns.py
index 654c4bcdd4..7e551be339 100644
--- a/src/calibre/gui2/preferences/columns.py
+++ b/src/calibre/gui2/preferences/columns.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/conversion.py b/src/calibre/gui2/preferences/conversion.py
index 05ecf02b90..37ff5db7c4 100644
--- a/src/calibre/gui2/preferences/conversion.py
+++ b/src/calibre/gui2/preferences/conversion.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -22,6 +23,7 @@ from calibre.gui2.convert.structure_detection import StructureDetectionWidget
 from calibre.gui2.convert.toc import TOCWidget
 from calibre.customize.ui import input_format_plugins, output_format_plugins
 from calibre.gui2.convert import config_widget_for_input_plugin
+from polyglot.builtins import unicode_type
 
 
 class Model(QStringListModel):
@@ -91,7 +93,7 @@ class Base(ConfigWidgetBase):
                         if rec.option == name:
                             ans = getattr(rec, 'help', None)
                             if ans is not None:
-                                return ans.replace('%default', str(rec.recommended_value))
+                                return ans.replace('%default', unicode_type(rec.recommended_value))
             return cls(self, self.plumber.get_option_by_name, hfunc, None, None)
 
         self.load_conversion_widgets()
diff --git a/src/calibre/gui2/preferences/create_custom_column.py b/src/calibre/gui2/preferences/create_custom_column.py
index 38fd20a80c..5df4752910 100644
--- a/src/calibre/gui2/preferences/create_custom_column.py
+++ b/src/calibre/gui2/preferences/create_custom_column.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid at kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/device_debug.py b/src/calibre/gui2/preferences/device_debug.py
index 2f6ba04286..6ea542e6e5 100644
--- a/src/calibre/gui2/preferences/device_debug.py
+++ b/src/calibre/gui2/preferences/device_debug.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/device_user_defined.py b/src/calibre/gui2/preferences/device_user_defined.py
index 40413593d8..88e02bf404 100644
--- a/src/calibre/gui2/preferences/device_user_defined.py
+++ b/src/calibre/gui2/preferences/device_user_defined.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/history.py b/src/calibre/gui2/preferences/history.py
index dc1ab07f50..951d3344ad 100644
--- a/src/calibre/gui2/preferences/history.py
+++ b/src/calibre/gui2/preferences/history.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/look_feel.py b/src/calibre/gui2/preferences/look_feel.py
index c6d5abe7b9..39d6770d96 100644
--- a/src/calibre/gui2/preferences/look_feel.py
+++ b/src/calibre/gui2/preferences/look_feel.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/main.py b/src/calibre/gui2/preferences/main.py
index 43f4386d5b..9da2fb0e96 100644
--- a/src/calibre/gui2/preferences/main.py
+++ b/src/calibre/gui2/preferences/main.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/misc.py b/src/calibre/gui2/preferences/misc.py
index 617d6a64ff..668d79ac51 100644
--- a/src/calibre/gui2/preferences/misc.py
+++ b/src/calibre/gui2/preferences/misc.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/plugboard.py b/src/calibre/gui2/preferences/plugboard.py
index 65dea1c87d..aab1e79623 100644
--- a/src/calibre/gui2/preferences/plugboard.py
+++ b/src/calibre/gui2/preferences/plugboard.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -24,7 +24,7 @@ from calibre.library.save_to_disk import plugboard_any_format_value, \
 from calibre.srv.content import plugboard_content_server_value, plugboard_content_server_formats
 from calibre.gui2.email import plugboard_email_value, plugboard_email_formats
 from calibre.utils.formatter import validation_formatter
-from polyglot.builtins import unicode_type
+from polyglot.builtins import native_string_type, unicode_type
 
 
 class ConfigWidget(ConfigWidgetBase, Ui_Form):
@@ -99,10 +99,10 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
             self.dest_widgets.append(w)
             self.fields_layout.addWidget(w, 5+i, 1, 1, 1)
 
-        self.edit_device.currentIndexChanged[str].connect(self.edit_device_changed)
-        self.edit_format.currentIndexChanged[str].connect(self.edit_format_changed)
-        self.new_device.currentIndexChanged[str].connect(self.new_device_changed)
-        self.new_format.currentIndexChanged[str].connect(self.new_format_changed)
+        self.edit_device.currentIndexChanged[native_string_type].connect(self.edit_device_changed)
+        self.edit_format.currentIndexChanged[native_string_type].connect(self.edit_format_changed)
+        self.new_device.currentIndexChanged[native_string_type].connect(self.new_device_changed)
+        self.new_format.currentIndexChanged[native_string_type].connect(self.new_format_changed)
         self.existing_plugboards.itemClicked.connect(self.existing_pb_clicked)
         self.ok_button.clicked.connect(self.ok_clicked)
         self.del_button.clicked.connect(self.del_clicked)
@@ -300,7 +300,7 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
                     except Exception as err:
                         error_dialog(self, _('Invalid template'),
                                 '<p>'+_('The template %s is invalid:')%s +
-                                '<br>'+str(err), show=True)
+                                '<br>'+unicode_type(err), show=True)
                         return
                     pb.append((s, self.dest_fields[d]))
                     comments_in_dests = comments_in_dests or self.dest_fields[d] == 'comments'
diff --git a/src/calibre/gui2/preferences/plugins.py b/src/calibre/gui2/preferences/plugins.py
index 21c53f0e7e..9f445c8938 100644
--- a/src/calibre/gui2/preferences/plugins.py
+++ b/src/calibre/gui2/preferences/plugins.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -204,7 +205,7 @@ class PluginModel(QAbstractItemModel, AdaptSQP):  # {{{
             plugin = self.index_to_plugin(index)
             disabled = is_disabled(plugin)
             if role == Qt.DisplayRole:
-                ver = '.'.join(map(str, plugin.version))
+                ver = '.'.join(map(unicode_type, plugin.version))
                 desc = '\n'.join(textwrap.wrap(plugin.description, 100))
                 ans='%s (%s) %s %s\n%s'%(plugin.name, ver, _('by'), plugin.author, desc)
                 c = plugin_customization(plugin)
diff --git a/src/calibre/gui2/preferences/save_template.py b/src/calibre/gui2/preferences/save_template.py
index 374d089214..281b184d3f 100644
--- a/src/calibre/gui2/preferences/save_template.py
+++ b/src/calibre/gui2/preferences/save_template.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -34,12 +34,12 @@ class SaveTemplate(QWidget, Ui_Form):
                 ' by clicking the device icon and choosing "Configure this device".'))
         rows = []
         for var in variables:
-            rows.append(u'<tr><td>%s</td><td>&nbsp;</td><td>%s</td></tr>'%
+            rows.append('<tr><td>%s</td><td>&nbsp;</td><td>%s</td></tr>'%
                     (var, FORMAT_ARG_DESCS[var]))
-        rows.append(u'<tr><td>%s&nbsp;</td><td>&nbsp;</td><td>%s</td></tr>'%(
+        rows.append('<tr><td>%s&nbsp;</td><td>&nbsp;</td><td>%s</td></tr>'%(
             _('Any custom field'),
             _('The lookup name of any custom field (these names begin with "#").')))
-        table = u'<table>%s</table>'%(u'\n'.join(rows))
+        table = '<table>%s</table>'%('\n'.join(rows))
         self.template_variables.setText(table)
 
         self.field_metadata = field_metadata
@@ -75,7 +75,7 @@ class SaveTemplate(QWidget, Ui_Form):
         except Exception as err:
             error_dialog(self, _('Invalid template'),
                     '<p>'+_('The template %s is invalid:')%tmpl +
-                    '<br>'+str(err), show=True)
+                    '<br>'+unicode_type(err), show=True)
             return False
         return True
 
diff --git a/src/calibre/gui2/preferences/saving.py b/src/calibre/gui2/preferences/saving.py
index e44c3f5dd6..98093f1cbc 100644
--- a/src/calibre/gui2/preferences/saving.py
+++ b/src/calibre/gui2/preferences/saving.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/search.py b/src/calibre/gui2/preferences/search.py
index e919ece61a..2df93f9ce8 100644
--- a/src/calibre/gui2/preferences/search.py
+++ b/src/calibre/gui2/preferences/search.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/sending.py b/src/calibre/gui2/preferences/sending.py
index 1b3776a289..6019517487 100644
--- a/src/calibre/gui2/preferences/sending.py
+++ b/src/calibre/gui2/preferences/sending.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/preferences/template_functions.py b/src/calibre/gui2/preferences/template_functions.py
index b8e0d49441..d4693e3dc9 100644
--- a/src/calibre/gui2/preferences/template_functions.py
+++ b/src/calibre/gui2/preferences/template_functions.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -16,7 +17,7 @@ from calibre.gui2.widgets import PythonHighlighter
 from calibre.utils.formatter_functions import (formatter_functions,
                         compile_user_function, compile_user_template_functions,
                         load_user_template_functions)
-from polyglot.builtins import iteritems, unicode_type
+from polyglot.builtins import iteritems, native_string_type, unicode_type
 
 
 class ConfigWidget(ConfigWidgetBase, Ui_Form):
@@ -89,7 +90,7 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
         self.builtins = formatter_functions().get_builtins_and_aliases()
 
         self.build_function_names_box()
-        self.function_name.currentIndexChanged[str].connect(self.function_index_changed)
+        self.function_name.currentIndexChanged[native_string_type].connect(self.function_index_changed)
         self.function_name.editTextChanged.connect(self.function_name_edited)
         self.argument_count.valueChanged.connect(self.enable_replace_button)
         self.documentation.textChanged.connect(self.enable_replace_button)
diff --git a/src/calibre/gui2/preferences/toolbar.py b/src/calibre/gui2/preferences/toolbar.py
index eec30a2859..4104f3a506 100644
--- a/src/calibre/gui2/preferences/toolbar.py
+++ b/src/calibre/gui2/preferences/toolbar.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/tag_browser/view.py b/src/calibre/gui2/tag_browser/view.py
index 5b9e224ad5..e5b144ece2 100644
--- a/src/calibre/gui2/tag_browser/view.py
+++ b/src/calibre/gui2/tag_browser/view.py
@@ -188,7 +188,7 @@ class TagsView(QTreeView):  # {{{
                     border: 1px solid #bfcde4;
                     border-radius: 6px;
                 }
-        '''.replace('PAD', str(gprefs['tag_browser_item_padding'])) + (
+        '''.replace('PAD', unicode_type(gprefs['tag_browser_item_padding'])) + (
             '' if gprefs['tag_browser_old_look'] else stylish_tb))
         self.setAlternatingRowColors(gprefs['tag_browser_old_look'])
         self.itemDelegate().old_look = gprefs['tag_browser_old_look']
diff --git a/src/calibre/gui2/toc/location.py b/src/calibre/gui2/toc/location.py
index f803c1461a..a76faae5b2 100644
--- a/src/calibre/gui2/toc/location.py
+++ b/src/calibre/gui2/toc/location.py
@@ -17,7 +17,7 @@ from PyQt5.QtWebKit import QWebElement
 from calibre.ebooks.oeb.display.webview import load_html
 from calibre.gui2 import error_dialog, question_dialog, gprefs, secure_web_page
 from calibre.utils.logging import default_log
-from polyglot.builtins import unicode_type, range
+from polyglot.builtins import native_string_type, range, unicode_type
 from polyglot.binary import as_base64_unicode
 
 
@@ -36,7 +36,7 @@ class Page(QWebPage):  # {{{
         self.setLinkDelegationPolicy(self.DelegateAllLinks)
 
     def javaScriptConsoleMessage(self, msg, lineno, msgid):
-        self.log(u'JS:', unicode_type(msg))
+        self.log('JS:', unicode_type(msg))
 
     def javaScriptAlert(self, frame, msg):
         self.log(unicode_type(msg))
@@ -45,11 +45,11 @@ class Page(QWebPage):  # {{{
     def shouldInterruptJavaScript(self):
         return True
 
-    @pyqtSlot(QWebElement, str, str, float)
+    @pyqtSlot(QWebElement, native_string_type, native_string_type, float)
     def onclick(self, elem, loc, totals, frac):
         elem_id = unicode_type(elem.attribute('id')) or None
         tag = unicode_type(elem.tagName()).lower()
-        self.elem_clicked.emit(tag, frac, elem_id, json.loads(str(loc)), json.loads(str(totals)))
+        self.elem_clicked.emit(tag, frac, elem_id, json.loads(unicode_type(loc)), json.loads(unicode_type(totals)))
 
     def load_js(self):
         if self.js is None:
diff --git a/src/calibre/gui2/toc/main.py b/src/calibre/gui2/toc/main.py
index 727bd7b678..f5a00b01ae 100644
--- a/src/calibre/gui2/toc/main.py
+++ b/src/calibre/gui2/toc/main.py
@@ -9,7 +9,6 @@ __docformat__ = 'restructuredtext en'
 import sys, os, textwrap
 from threading import Thread
 from functools import partial
-from polyglot.builtins import map, unicode_type, range
 
 from PyQt5.Qt import (QPushButton, QFrame, QMenu, QInputDialog, QCheckBox,
     QDialog, QVBoxLayout, QDialogButtonBox, QSize, QStackedWidget, QWidget,
@@ -24,6 +23,7 @@ from calibre.gui2.progress_indicator import ProgressIndicator
 from calibre.gui2.toc.location import ItemEdit
 from calibre.gui2.convert.xpath_wizard import XPathEdit
 from calibre.utils.logging import GUILog
+from polyglot.builtins import map, unicode_type, range
 
 ICON_SIZE = 24
 
@@ -80,7 +80,7 @@ class XPathDialog(QDialog):  # {{{
             if name:
                 saved = self.prefs.get('xpath_toc_settings', {})
                 # in JSON all keys have to be strings
-                saved[name] = {str(i):x for i, x in enumerate(xpaths)}
+                saved[name] = {unicode_type(i):x for i, x in enumerate(xpaths)}
                 self.prefs.set('xpath_toc_settings', saved)
                 self.setup_load_button()
 
@@ -103,7 +103,7 @@ class XPathDialog(QDialog):  # {{{
     def load_settings(self, name):
         saved = self.prefs.get('xpath_toc_settings', {}).get(name, {})
         for i, w in enumerate(self.widgets):
-            txt = saved.get(str(i), '')
+            txt = saved.get(unicode_type(i), '')
             w.edit.setText(txt)
 
     def check(self):
diff --git a/src/calibre/gui2/tweak_book/char_select.py b/src/calibre/gui2/tweak_book/char_select.py
index 541163d5ac..61c619f822 100644
--- a/src/calibre/gui2/tweak_book/char_select.py
+++ b/src/calibre/gui2/tweak_book/char_select.py
@@ -520,7 +520,7 @@ class CharModel(QAbstractListModel):
         return ['application/calibre_charcode_indices']
 
     def mimeData(self, indexes):
-        data = ','.join(str(i.row()) for i in indexes)
+        data = ','.join(unicode_type(i.row()) for i in indexes)
         md = QMimeData()
         md.setData('application/calibre_charcode_indices', data.encode('utf-8'))
         return md
diff --git a/src/calibre/gui2/tweak_book/file_list.py b/src/calibre/gui2/tweak_book/file_list.py
index 1762386469..d13e63cb16 100644
--- a/src/calibre/gui2/tweak_book/file_list.py
+++ b/src/calibre/gui2/tweak_book/file_list.py
@@ -118,7 +118,7 @@ def get_bulk_rename_settings(parent, number, msg=None, sanitize=sanitize_file_na
         fmt = '%d'
         if leading_zeros:
             largest = num + number - 1
-            fmt = '%0{0}d'.format(len(str(largest)))
+            fmt = '%0{0}d'.format(len(unicode_type(largest)))
         ans['prefix'] = prefix + fmt
         ans['start'] = num
         if allow_spine_order:
diff --git a/src/calibre/gui2/tweak_book/preview.py b/src/calibre/gui2/tweak_book/preview.py
index f86a8fa6bd..ed4320eb22 100644
--- a/src/calibre/gui2/tweak_book/preview.py
+++ b/src/calibre/gui2/tweak_book/preview.py
@@ -7,7 +7,6 @@ __copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 
 import time, textwrap, json
 from bisect import bisect_right
-from polyglot.builtins import map, unicode_type, filter
 from threading import Thread
 from functools import partial
 
@@ -27,6 +26,7 @@ from calibre.gui2.viewer.documentview import apply_settings
 from calibre.gui2.viewer.config import config
 from calibre.gui2.widgets2 import HistoryLineEdit2
 from calibre.utils.ipc.simple_worker import offload_worker
+from polyglot.builtins import filter, map, native_string_type, unicode_type
 from polyglot.urllib import urlparse
 from polyglot.queue import Queue, Empty
 from polyglot.binary import as_base64_unicode
@@ -295,7 +295,7 @@ class WebPage(QWebPage):
         mf.addToJavaScriptWindowObject("py_bridge", self)
         mf.evaluateJavaScript(self.js)
 
-    @pyqtSlot(str, str, str)
+    @pyqtSlot(native_string_type, native_string_type, native_string_type)
     def request_sync(self, tag_name, href, sourceline_address):
         try:
             self.sync_requested.emit(unicode_type(tag_name), unicode_type(href), json.loads(unicode_type(sourceline_address)))
@@ -304,9 +304,9 @@ class WebPage(QWebPage):
 
     def go_to_anchor(self, anchor, lnum):
         self.mainFrame().evaluateJavaScript('window.calibre_preview_integration.go_to_anchor(%s, %s)' % (
-            json.dumps(anchor), json.dumps(str(lnum))))
+            json.dumps(anchor), json.dumps(unicode_type(lnum))))
 
-    @pyqtSlot(str, str)
+    @pyqtSlot(native_string_type, native_string_type)
     def request_split(self, loc, totals):
         actions['split-in-preview'].setChecked(False)
         loc, totals = json.loads(unicode_type(loc)), json.loads(unicode_type(totals))
diff --git a/src/calibre/gui2/tweak_book/reports.py b/src/calibre/gui2/tweak_book/reports.py
index df729f5844..81a19e0853 100644
--- a/src/calibre/gui2/tweak_book/reports.py
+++ b/src/calibre/gui2/tweak_book/reports.py
@@ -7,7 +7,6 @@ __copyright__ = '2015, Kovid Goyal <kovid at kovidgoyal.net>'
 
 import time, textwrap, os
 from threading import Thread
-from polyglot.builtins import iteritems, map, range, filter
 from operator import itemgetter
 from functools import partial
 from collections import defaultdict
@@ -35,6 +34,7 @@ from calibre.gui2.progress_indicator import ProgressIndicator
 from calibre.utils.icu import primary_contains, numeric_sort_key
 from calibre.utils.unicode_names import character_name_from_code
 from calibre.utils.localization import calibre_langcode_to_name, canonicalize_lang
+from polyglot.builtins import filter, iteritems, map, range, unicode_type
 
 # Utils {{{
 
@@ -980,7 +980,7 @@ class CSSRulesModel(QAbstractItemModel):
         self.rules = data['css']
         self.num_unused = sum(1 for r in self.rules if r.count == 0)
         try:
-            self.num_size = len(str(max(r.count for r in self.rules)))
+            self.num_size = len(unicode_type(max(r.count for r in self.rules)))
         except ValueError:
             self.num_size = 1
         self.build_maps()
@@ -1204,7 +1204,7 @@ class ClassesModel(CSSRulesModel):
         self.rules = self.classes = tuple(data['classes'])
         self.num_unused = sum(1 for ce in self.classes if ce.num_of_matches == 0)
         try:
-            self.num_size = len(str(max(r.num_of_matches for r in self.classes)))
+            self.num_size = len(unicode_type(max(r.num_of_matches for r in self.classes)))
         except ValueError:
             self.num_size = 1
         self.build_maps()
diff --git a/src/calibre/gui2/viewer/documentview.py b/src/calibre/gui2/viewer/documentview.py
index 7632e62548..d055186000 100644
--- a/src/calibre/gui2/viewer/documentview.py
+++ b/src/calibre/gui2/viewer/documentview.py
@@ -1,4 +1,6 @@
 #!/usr/bin/env  python2
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal kovid@kovidgoyal.net'
 __docformat__ = 'restructuredtext en'
@@ -6,7 +8,6 @@ __docformat__ = 'restructuredtext en'
 # Imports {{{
 import math, json
 from functools import partial
-from polyglot.builtins import iteritems, map, unicode_type, string_or_bytes
 
 from PyQt5.Qt import (
     QSize, QSizePolicy, QUrl, Qt, QPainter, QPalette, QBrush,
@@ -32,6 +33,7 @@ from calibre.gui2.viewer.footnote import Footnotes
 from calibre.gui2.viewer.fake_net import NetworkAccessManager
 from calibre.ebooks.oeb.display.webview import load_html
 from calibre.constants import isxp, iswindows, DEBUG, __version__
+from polyglot.builtins import iteritems, map, unicode_type, string_or_bytes
 from polyglot.binary import as_base64_unicode
 # }}}
 
@@ -205,7 +207,7 @@ class Document(QWebPage):  # {{{
         evaljs('window.calibre_utils.setup_epub_reading_system(%s, %s, %s, %s)' % tuple(map(json.dumps, (
             'calibre-desktop', __version__, 'paginated' if self.in_paged_mode else 'scrolling',
             'dom-manipulation layout-changes mouse-events keyboard-events'.split()))))
-        self.javascript(u'window.mathjax.base = %s'%(json.dumps(self.nam.mathjax_base, ensure_ascii=False)))
+        self.javascript('window.mathjax.base = %s'%(json.dumps(self.nam.mathjax_base, ensure_ascii=False)))
         for pl in self.all_viewer_plugins:
             pl.load_javascript(evaljs)
         evaljs('py_bridge.mark_element.connect(window.calibre_extract.mark)')
@@ -299,7 +301,7 @@ class Document(QWebPage):  # {{{
     def column_boundaries(self):
         if not self.loaded_javascript:
             return (0, 1)
-        ans = self.javascript(u'JSON.stringify(paged_display.column_boundaries())')
+        ans = self.javascript('JSON.stringify(paged_display.column_boundaries())')
         return tuple(int(x) for x in json.loads(ans))
 
     def after_resize(self):
@@ -359,7 +361,7 @@ class Document(QWebPage):  # {{{
             except (TypeError, ValueError):
                 return 0.0
         if typ == 'string':
-            return ans or u''
+            return ans or ''
         if typ in {bool, 'bool'}:
             return bool(ans)
         return ans
@@ -656,11 +658,11 @@ class DocumentView(QWebView):  # {{{
 
     @property
     def selected_text(self):
-        return self.document.selectedText().replace(u'\u00ad', u'').strip()
+        return self.document.selectedText().replace('\u00ad', '').strip()
 
     @property
     def selected_html(self):
-        return self.document.selectedHtml().replace(u'\u00ad', u'').strip()
+        return self.document.selectedHtml().replace('\u00ad', '').strip()
 
     def selection_changed(self):
         if self.manager is not None:
@@ -669,10 +671,10 @@ class DocumentView(QWebView):  # {{{
     def _selectedText(self):
         t = unicode_type(self.selectedText()).strip()
         if not t:
-            return u''
+            return ''
         if len(t) > 40:
-            t = t[:40] + u'...'
-        t = t.replace(u'&', u'&&')
+            t = t[:40] + '...'
+        t = t.replace('&', '&&')
         return _("S&earch online for '%s'")%t
 
     def popup_table(self):
@@ -696,7 +698,7 @@ class DocumentView(QWebView):  # {{{
         table = None
         parent = elem
         while not parent.isNull():
-            if (unicode_type(parent.tagName()) == u'table' or unicode_type(parent.localName()) == u'table'):
+            if (unicode_type(parent.tagName()) == 'table' or unicode_type(parent.localName()) == 'table'):
                 table = parent
                 break
             parent = parent.parent()
@@ -937,7 +939,7 @@ class DocumentView(QWebView):  # {{{
                 self.scrollbar.setRange(0, delta)
                 self.scrollbar.setValue(0)
                 self.scrollbar.setSingleStep(1)
-                self.scrollbar.setPageStep(int(delta/10.))
+                self.scrollbar.setPageStep(int(delta//10))
             self.scrollbar.setVisible(delta > 0)
             self.scrollbar.blockSignals(False)
             self._ignore_scrollbar_signals = False
@@ -1294,7 +1296,7 @@ class DocumentView(QWebView):  # {{{
         amt =  dim * scroll_amount
         mult = -1 if amt < 0 else 1
         if self.document.wheel_scroll_fraction != 100:
-            amt = mult * max(1, abs(int(amt * self.document.wheel_scroll_fraction / 100.)))
+            amt = mult * max(1, abs(int(amt * self.document.wheel_scroll_fraction / 100)))
         self.scroll_by(0, amt) if vertical else self.scroll_by(amt, 0)
 
         if self.manager is not None:
@@ -1334,7 +1336,7 @@ class DocumentView(QWebView):  # {{{
                 if (not self.document.line_scrolling_stops_on_pagebreaks and self.document.at_bottom):
                     self.manager.next_document()
                 else:
-                    amt = int((self.document.line_scroll_fraction / 100.) * 15)
+                    amt = int((self.document.line_scroll_fraction / 100) * 15)
                     self.scroll_by(y=amt)
         elif key == 'Up':
             if self.document.in_paged_mode:
@@ -1344,19 +1346,19 @@ class DocumentView(QWebView):  # {{{
                 if (not self.document.line_scrolling_stops_on_pagebreaks and self.document.at_top):
                     self.manager.previous_document()
                 else:
-                    amt = int((self.document.line_scroll_fraction / 100.) * 15)
+                    amt = int((self.document.line_scroll_fraction / 100) * 15)
                     self.scroll_by(y=-amt)
         elif key == 'Left':
             if self.document.in_paged_mode:
                 self.paged_col_scroll(forward=False)
             else:
-                amt = int((self.document.line_scroll_fraction / 100.) * 15)
+                amt = int((self.document.line_scroll_fraction / 100) * 15)
                 self.scroll_by(x=-amt)
         elif key == 'Right':
             if self.document.in_paged_mode:
                 self.paged_col_scroll()
             else:
-                amt = int((self.document.line_scroll_fraction / 100.) * 15)
+                amt = int((self.document.line_scroll_fraction / 100) * 15)
                 self.scroll_by(x=amt)
         elif key == 'Back':
             if self.manager is not None:
diff --git a/src/calibre/gui2/viewer/fake_net.py b/src/calibre/gui2/viewer/fake_net.py
index 84fd930a46..03de232888 100644
--- a/src/calibre/gui2/viewer/fake_net.py
+++ b/src/calibre/gui2/viewer/fake_net.py
@@ -1,8 +1,8 @@
 #!/usr/bin/env python2
 # vim:fileencoding=utf-8
 # License: GPLv3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
-
 from __future__ import absolute_import, division, print_function, unicode_literals
+
 import os
 
 from PyQt5.Qt import QNetworkReply, QNetworkAccessManager, QUrl, QNetworkRequest, QTimer, pyqtSignal, QByteArray
@@ -12,6 +12,7 @@ from calibre.constants import FAKE_HOST, FAKE_PROTOCOL, DEBUG
 from calibre.ebooks.oeb.base import OEB_DOCS
 from calibre.ebooks.oeb.display.webview import cleanup_html, load_as_html
 from calibre.utils.short_uuid import uuid4
+from polyglot.builtins import unicode_type
 
 
 def guess_type(x):
@@ -101,7 +102,7 @@ class NetworkAccessManager(QNetworkAccessManager):
 
     def __init__(self, parent=None):
         QNetworkAccessManager.__init__(self, parent)
-        self.mathjax_prefix = str(uuid4())
+        self.mathjax_prefix = unicode_type(uuid4())
         self.mathjax_base = '%s://%s/%s/' % (FAKE_PROTOCOL, FAKE_HOST, self.mathjax_prefix)
         self.root = self.orig_root = os.path.dirname(P('viewer/blank.html', allow_user_override=False))
         self.mime_map, self.single_pages, self.codec_map = {}, set(), {}
diff --git a/src/calibre/gui2/viewer/flip.py b/src/calibre/gui2/viewer/flip.py
index 185c4d6d4a..72103e0847 100644
--- a/src/calibre/gui2/viewer/flip.py
+++ b/src/calibre/gui2/viewer/flip.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -113,5 +114,3 @@ class SlideFlip(QWidget):
             fget=lambda self: self._current_width,
             fset=set_current_width
             )
-
-
diff --git a/src/calibre/gui2/viewer/keys.py b/src/calibre/gui2/viewer/keys.py
index 178aee985a..8e09eb8336 100644
--- a/src/calibre/gui2/viewer/keys.py
+++ b/src/calibre/gui2/viewer/keys.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/gui2/viewer/main.py b/src/calibre/gui2/viewer/main.py
index 1867ba807e..ecb666c044 100644
--- a/src/calibre/gui2/viewer/main.py
+++ b/src/calibre/gui2/viewer/main.py
@@ -1,8 +1,8 @@
 #!/usr/bin/env python2
 # vim:fileencoding=utf-8
 # License: GPLv3 Copyright: 2015, Kovid Goyal <kovid at kovidgoyal.net>
+from __future__ import absolute_import, division, print_function, unicode_literals
 
-from __future__ import print_function
 import functools
 import os
 import sys
@@ -421,7 +421,7 @@ class EbookViewer(MainWindow):
 
     def lookup(self, word):
         from polyglot.urllib import quote
-        word = word.replace(u'\u00ad', '')
+        word = word.replace('\u00ad', '')
         word = quote(word.encode('utf-8'))
         lang = canonicalize_lang(self.view.current_language) or get_lang() or 'en'
         try:
diff --git a/src/calibre/gui2/wizard/__init__.py b/src/calibre/gui2/wizard/__init__.py
index abb00ecece..dc36271108 100644
--- a/src/calibre/gui2/wizard/__init__.py
+++ b/src/calibre/gui2/wizard/__init__.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -9,7 +9,6 @@ __docformat__ = 'restructuredtext en'
 import os, traceback, re
 from contextlib import closing
 
-
 from PyQt5.Qt import (QWizard, QWizardPage, QIcon, Qt, QAbstractListModel,
     QItemSelectionModel, pyqtSignal, QItemSelection, QDir)
 from calibre import __appname__
@@ -573,7 +572,7 @@ class StanzaPage(QWizardPage, StanzaUI):
                 try:
                     s.bind(('0.0.0.0', p))
                     t = unicode_type(self.instructions.text())
-                    t = re.sub(r':\d+', ':'+str(p), t)
+                    t = re.sub(r':\d+', ':'+unicode_type(p), t)
                     self.instructions.setText(t)
                     return p
                 except:
@@ -686,10 +685,10 @@ class LibraryPage(QWizardPage, LibraryUI):
         for item in items:
             self.language.addItem(item[1], (item[0]))
         self.language.blockSignals(False)
-        prefs['language'] = str(self.language.itemData(self.language.currentIndex()) or '')
+        prefs['language'] = unicode_type(self.language.itemData(self.language.currentIndex()) or '')
 
     def change_language(self, idx):
-        prefs['language'] = str(self.language.itemData(self.language.currentIndex()) or '')
+        prefs['language'] = unicode_type(self.language.itemData(self.language.currentIndex()) or '')
         from polyglot.builtins import builtins
         builtins.__dict__['_'] = lambda x: x
         from calibre.utils.localization import set_translators
@@ -766,7 +765,7 @@ class LibraryPage(QWizardPage, LibraryUI):
         if not lp:
             fname = _('Calibre Library')
             try:
-                base = os.path.expanduser(u'~')
+                base = os.path.expanduser('~')
             except ValueError:
                 base = QDir.homePath().replace('/', os.sep)
 
@@ -778,7 +777,7 @@ class LibraryPage(QWizardPage, LibraryUI):
                 except:
                     traceback.print_exc()
                     try:
-                        lp = os.path.expanduser(u'~')
+                        lp = os.path.expanduser('~')
                     except ValueError:
                         lp = QDir.homePath().replace('/', os.sep)
         self.location.setText(lp)
diff --git a/src/calibre/gui2/wizard/send_email.py b/src/calibre/gui2/wizard/send_email.py
index 4df152d0d9..f2ca746e87 100644
--- a/src/calibre/gui2/wizard/send_email.py
+++ b/src/calibre/gui2/wizard/send_email.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/library/check_library.py b/src/calibre/library/check_library.py
index 944f4af160..6990ad5dea 100644
--- a/src/calibre/library/check_library.py
+++ b/src/calibre/library/check_library.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/library/custom_columns.py b/src/calibre/library/custom_columns.py
index 1d73744a06..843341447d 100644
--- a/src/calibre/library/custom_columns.py
+++ b/src/calibre/library/custom_columns.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -136,7 +136,7 @@ class CustomColumns(object):
                 x = [y.strip() for y in x if y.strip()]
                 x = [y.decode(preferred_encoding, 'replace') if not isinstance(y,
                     unicode_type) else y for y in x]
-                return [u' '.join(y.split()) for y in x]
+                return [' '.join(y.split()) for y in x]
             else:
                 return x if x is None or isinstance(x, unicode_type) else \
                         x.decode(preferred_encoding, 'replace')
diff --git a/src/calibre/library/field_metadata.py b/src/calibre/library/field_metadata.py
index 27a6d29d6f..5e385b9a9f 100644
--- a/src/calibre/library/field_metadata.py
+++ b/src/calibre/library/field_metadata.py
@@ -1,8 +1,11 @@
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 '''
 Created on 25 May 2010
 
 @author: charles
 '''
+
 import traceback
 from collections import OrderedDict
 
diff --git a/src/calibre/library/prefs.py b/src/calibre/library/prefs.py
index 9ef2214da8..87cbaef947 100644
--- a/src/calibre/library/prefs.py
+++ b/src/calibre/library/prefs.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
@@ -63,19 +64,19 @@ class DBPrefs(dict):
         self.__setitem__(key, val)
 
     def get_namespaced(self, namespace, key, default=None):
-        key = u'namespaced:%s:%s'%(namespace, key)
+        key = 'namespaced:%s:%s'%(namespace, key)
         try:
             return dict.__getitem__(self, key)
         except KeyError:
             return default
 
     def set_namespaced(self, namespace, key, val):
-        if u':' in key:
+        if ':' in key:
             raise KeyError('Colons are not allowed in keys')
-        if u':' in namespace:
+        if ':' in namespace:
             raise KeyError('Colons are not allowed in'
                 ' the namespace')
-        key = u'namespaced:%s:%s'%(namespace, key)
+        key = 'namespaced:%s:%s'%(namespace, key)
         self[key] = val
 
     def write_serialized(self, library_path):
diff --git a/src/duktape/__init__.py b/src/duktape/__init__.py
index eef389a0c3..f68317cbe1 100644
--- a/src/duktape/__init__.py
+++ b/src/duktape/__init__.py
@@ -12,11 +12,10 @@ import errno, os, sys, numbers, hashlib, json
 from functools import partial
 
 import dukpy
-from polyglot.builtins import reraise
 
 from calibre.constants import iswindows
 from calibre.utils.filenames import atomic_rename
-from polyglot.builtins import error_message, getcwd
+from polyglot.builtins import error_message, getcwd, reraise, unicode_type
 
 Context_, undefined = dukpy.Context, dukpy.undefined
 
@@ -112,7 +111,7 @@ def load_file(base_dirs, builtin_modules, name):
                     raise
         raise EnvironmentError('No module named: %s found in the base directories: %s' % (name, os.pathsep.join(base_dirs)))
     except Exception as e:
-        return [False, str(e)]
+        return [False, unicode_type(e)]
 
 
 def readfile(path, enc='utf-8'):
@@ -156,7 +155,7 @@ class Function(object):
     def __repr__(self):
         # For some reason x._Formals is undefined in duktape
         x = self.func
-        return str('[Function: %s(...) from file: %s]' % (x.name, x.fileName))
+        return unicode_type('[Function: %s(...) from file: %s]' % (x.name, x.fileName))
 
     def __call__(self, *args, **kwargs):
         try: