diff --git a/src/calibre/ebooks/conversion/plugins/azw4_input.py b/src/calibre/ebooks/conversion/plugins/azw4_input.py
index 7bceded58f..d3a7e6a5f9 100644
--- a/src/calibre/ebooks/conversion/plugins/azw4_input.py
+++ b/src/calibre/ebooks/conversion/plugins/azw4_input.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2011, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/chm_input.py b/src/calibre/ebooks/conversion/plugins/chm_input.py
index 01b81bbbec..b87c347ca0 100644
--- a/src/calibre/ebooks/conversion/plugins/chm_input.py
+++ b/src/calibre/ebooks/conversion/plugins/chm_input.py
@@ -1,3 +1,5 @@
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 ''' CHM File decoding support '''
 __license__ = 'GPL v3'
 __copyright__  = '2008, Kovid Goyal <kovid at kovidgoyal.net>,' \
@@ -64,7 +66,7 @@ class CHMInput(InputFormatPlugin):
                 metadata = Metadata(os.path.basename(chm_name))
             encoding = self._chm_reader.get_encoding() or options.input_encoding or 'cp1252'
             self._chm_reader.CloseCHM()
-            # print tdir, mainpath
+            # print((tdir, mainpath))
             # from calibre import ipython
             # ipython()
 
@@ -117,10 +119,10 @@ class CHMInput(InputFormatPlugin):
                             strip_encoding_pats=True, resolve_entities=True)[0]
         hhcroot = html.fromstring(hhcdata)
         toc = self._process_nodes(hhcroot)
-        # print "============================="
-        # print "Printing hhcroot"
-        # print etree.tostring(hhcroot, pretty_print=True)
-        # print "============================="
+        # print("=============================")
+        # print("Printing hhcroot")
+        # print(etree.tostring(hhcroot, pretty_print=True))
+        # print("=============================")
         log.debug('Found %d section nodes' % toc.count())
         htmlpath = os.path.splitext(hhcpath)[0] + ".html"
         base = os.path.dirname(os.path.abspath(htmlpath))
@@ -183,7 +185,7 @@ class CHMInput(InputFormatPlugin):
             p = node.xpath('ancestor::ul[1]/ancestor::li[1]/object[1]')
             parent = p[0] if p else None
             toc = ancestor_map.get(parent, toc)
-            title = href = u''
+            title = href = ''
             for param in node.xpath('./param'):
                 if match_string(param.attrib['name'], 'name'):
                     title = param.attrib['value']
diff --git a/src/calibre/ebooks/conversion/plugins/epub_input.py b/src/calibre/ebooks/conversion/plugins/epub_input.py
index 1df6813eb3..983d7b0d10 100644
--- a/src/calibre/ebooks/conversion/plugins/epub_input.py
+++ b/src/calibre/ebooks/conversion/plugins/epub_input.py
@@ -1,4 +1,5 @@
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__ = 'GPL 3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
@@ -44,7 +45,7 @@ class EPUBInput(InputFormatPlugin):
         import uuid, hashlib
         idpf_key = opf.raw_unique_identifier
         if idpf_key:
-            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 opf.identifier_iter():
@@ -269,7 +270,7 @@ class EPUBInput(InputFormatPlugin):
         encfile = os.path.abspath(os.path.join('META-INF', 'encryption.xml'))
         opf = self.find_opf()
         if opf is None:
-            for f in walk(u'.'):
+            for f in walk('.'):
                 if f.lower().endswith('.opf') and '__MACOSX' not in f and \
                         not os.path.basename(f).startswith('.'):
                     opf = os.path.abspath(f)
diff --git a/src/calibre/ebooks/conversion/plugins/fb2_output.py b/src/calibre/ebooks/conversion/plugins/fb2_output.py
index f86e6b39da..0313086bb4 100644
--- a/src/calibre/ebooks/conversion/plugins/fb2_output.py
+++ b/src/calibre/ebooks/conversion/plugins/fb2_output.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/lit_input.py b/src/calibre/ebooks/conversion/plugins/lit_input.py
index 78d858e49c..aa8f0c2925 100644
--- a/src/calibre/ebooks/conversion/plugins/lit_input.py
+++ b/src/calibre/ebooks/conversion/plugins/lit_input.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/ebooks/conversion/plugins/lit_output.py b/src/calibre/ebooks/conversion/plugins/lit_output.py
index f6f7a8cba3..a0d9a7f1a9 100644
--- a/src/calibre/ebooks/conversion/plugins/lit_output.py
+++ b/src/calibre/ebooks/conversion/plugins/lit_output.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/ebooks/conversion/plugins/lrf_input.py b/src/calibre/ebooks/conversion/plugins/lrf_input.py
index 926b6a2c29..e69654540d 100644
--- a/src/calibre/ebooks/conversion/plugins/lrf_input.py
+++ b/src/calibre/ebooks/conversion/plugins/lrf_input.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>'
@@ -85,4 +85,4 @@ class LRFInput(InputFormatPlugin):
         with open('content.opf', 'wb') as f:
             f.write(result)
         styles.write()
-        return os.path.abspath(u'content.opf')
+        return os.path.abspath('content.opf')
diff --git a/src/calibre/ebooks/conversion/plugins/lrf_output.py b/src/calibre/ebooks/conversion/plugins/lrf_output.py
index edae1f5688..88b6a6885d 100644
--- a/src/calibre/ebooks/conversion/plugins/lrf_output.py
+++ b/src/calibre/ebooks/conversion/plugins/lrf_output.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>'
@@ -188,7 +188,7 @@ class LRFOutput(OutputFormatPlugin):
         self.flatten_toc()
 
         from calibre.ptempfile import TemporaryDirectory
-        with TemporaryDirectory(u'_lrf_output') as tdir:
+        with TemporaryDirectory('_lrf_output') as tdir:
             from calibre.customize.ui import plugin_for_output_format
             oeb_output = plugin_for_output_format('oeb')
             oeb_output.convert(oeb, tdir, input_plugin, opts, log)
diff --git a/src/calibre/ebooks/conversion/plugins/mobi_input.py b/src/calibre/ebooks/conversion/plugins/mobi_input.py
index e9a89b5860..90a2dedd89 100644
--- a/src/calibre/ebooks/conversion/plugins/mobi_input.py
+++ b/src/calibre/ebooks/conversion/plugins/mobi_input.py
@@ -1,4 +1,5 @@
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__ = 'GPL 3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
@@ -29,13 +30,13 @@ class MOBIInput(InputFormatPlugin):
             mr = MobiReader(stream, log, options.input_encoding,
                         options.debug_pipeline)
             if mr.kf8_type is None:
-                mr.extract_content(u'.', parse_cache)
+                mr.extract_content('.', parse_cache)
 
         except:
             mr = MobiReader(stream, log, options.input_encoding,
                         options.debug_pipeline, try_extra_data_fix=True)
             if mr.kf8_type is None:
-                mr.extract_content(u'.', parse_cache)
+                mr.extract_content('.', parse_cache)
 
         if mr.kf8_type is not None:
             log('Found KF8 MOBI of type %r'%mr.kf8_type)
@@ -52,7 +53,7 @@ class MOBIInput(InputFormatPlugin):
         if raw:
             if isinstance(raw, unicode_type):
                 raw = raw.encode('utf-8')
-            with open(u'debug-raw.html', 'wb') as f:
+            with open('debug-raw.html', 'wb') as f:
                 f.write(raw)
         from calibre.ebooks.oeb.base import close_self_closing_tags
         for f, root in parse_cache.items():
diff --git a/src/calibre/ebooks/conversion/plugins/mobi_output.py b/src/calibre/ebooks/conversion/plugins/mobi_output.py
index ee939f26be..28cff521bc 100644
--- a/src/calibre/ebooks/conversion/plugins/mobi_output.py
+++ b/src/calibre/ebooks/conversion/plugins/mobi_output.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/ebooks/conversion/plugins/odt_input.py b/src/calibre/ebooks/conversion/plugins/odt_input.py
index fa71161213..f2f045b977 100644
--- a/src/calibre/ebooks/conversion/plugins/odt_input.py
+++ b/src/calibre/ebooks/conversion/plugins/odt_input.py
@@ -1,4 +1,5 @@
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal kovid@kovidgoyal.net'
 __docformat__ = 'restructuredtext en'
diff --git a/src/calibre/ebooks/conversion/plugins/oeb_output.py b/src/calibre/ebooks/conversion/plugins/oeb_output.py
index c5146e0001..417701433d 100644
--- a/src/calibre/ebooks/conversion/plugins/oeb_output.py
+++ b/src/calibre/ebooks/conversion/plugins/oeb_output.py
@@ -1,4 +1,5 @@
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__ = 'GPL 3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
diff --git a/src/calibre/ebooks/conversion/plugins/pdb_input.py b/src/calibre/ebooks/conversion/plugins/pdb_input.py
index 970b605a14..a55a4ffec3 100644
--- a/src/calibre/ebooks/conversion/plugins/pdb_input.py
+++ b/src/calibre/ebooks/conversion/plugins/pdb_input.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/pdb_output.py b/src/calibre/ebooks/conversion/plugins/pdb_output.py
index 0fc5662ccd..de450c175d 100644
--- a/src/calibre/ebooks/conversion/plugins/pdb_output.py
+++ b/src/calibre/ebooks/conversion/plugins/pdb_output.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/pdf_input.py b/src/calibre/ebooks/conversion/plugins/pdf_input.py
index 4bbebb01bf..242d64b980 100644
--- a/src/calibre/ebooks/conversion/plugins/pdf_input.py
+++ b/src/calibre/ebooks/conversion/plugins/pdf_input.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
@@ -38,7 +39,7 @@ class PDFInput(InputFormatPlugin):
         with open(u'index.xml', 'rb') as f:
             xml = clean_ascii_chars(f.read())
         PDFDocument(xml, self.opts, self.log)
-        return os.path.join(getcwd(), u'metadata.opf')
+        return os.path.join(getcwd(), 'metadata.opf')
 
     def convert(self, stream, options, file_ext, log,
                 accelerators):
@@ -57,7 +58,7 @@ class PDFInput(InputFormatPlugin):
         mi = get_metadata(stream, 'pdf')
         opf = OPFCreator(getcwd(), mi)
 
-        manifest = [(u'index.html', None)]
+        manifest = [('index.html', None)]
 
         images = os.listdir(getcwd())
         images.remove('index.html')
@@ -66,16 +67,16 @@ class PDFInput(InputFormatPlugin):
         log.debug('Generating manifest...')
         opf.create_manifest(manifest)
 
-        opf.create_spine([u'index.html'])
+        opf.create_spine(['index.html'])
         log.debug('Rendering manifest...')
-        with open(u'metadata.opf', 'wb') as opffile:
+        with open('metadata.opf', 'wb') as opffile:
             opf.render(opffile)
-        if os.path.exists(u'toc.ncx'):
+        if os.path.exists('toc.ncx'):
             ncxid = opf.manifest.id_for_path('toc.ncx')
             if ncxid:
-                with open(u'metadata.opf', 'r+b') as f:
+                with open('metadata.opf', 'r+b') as f:
                     raw = f.read().replace(b'<spine', b'<spine toc="%s"' % as_bytes(ncxid))
                     f.seek(0)
                     f.write(raw)
 
-        return os.path.join(getcwd(), u'metadata.opf')
+        return os.path.join(getcwd(), 'metadata.opf')
diff --git a/src/calibre/ebooks/conversion/plugins/pdf_output.py b/src/calibre/ebooks/conversion/plugins/pdf_output.py
index ae6c375ad7..99b20e1826 100644
--- a/src/calibre/ebooks/conversion/plugins/pdf_output.py
+++ b/src/calibre/ebooks/conversion/plugins/pdf_output.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2012, Kovid Goyal <kovid at kovidgoyal.net>'
@@ -30,7 +31,7 @@ class PDFMetadata(object):  # {{{
         from calibre.ebooks.metadata import authors_to_string
         self.title = _(u'Unknown')
         self.author = _(u'Unknown')
-        self.tags = u''
+        self.tags = ''
         self.mi = mi
 
         if mi is not None:
@@ -39,7 +40,7 @@ class PDFMetadata(object):  # {{{
             if mi.authors:
                 self.author = authors_to_string(mi.authors)
             if mi.tags:
-                self.tags = u', '.join(mi.tags)
+                self.tags = ', '.join(mi.tags)
 
         self.title = force_unicode(self.title)
         self.author = force_unicode(self.author)
@@ -242,16 +243,16 @@ class PDFOutput(OutputFormatPlugin):
                 elif iswindows and rule.type == rule.STYLE_RULE:
                     from tinycss.fonts3 import parse_font_family, serialize_font_family
                     s = rule.style
-                    f = s.getProperty(u'font-family')
+                    f = s.getProperty('font-family')
                     if f is not None:
                         font_families = parse_font_family(css_text(f.propertyValue))
-                        ff = [x for x in font_families if x.lower() != u'courier']
+                        ff = [x for x in font_families if x.lower() != 'courier']
                         if len(ff) != len(font_families):
                             if 'courier' not in self.filtered_font_warnings:
                                 # See https://bugs.launchpad.net/bugs/1665835
-                                self.filtered_font_warnings.add(u'courier')
-                                self.log.warn(u'Removing courier font family as it does not render on windows')
-                            f.propertyValue.cssText = serialize_font_family(ff or [u'monospace'])
+                                self.filtered_font_warnings.add('courier')
+                                self.log.warn('Removing courier font family as it does not render on windows')
+                            f.propertyValue.cssText = serialize_font_family(ff or ['monospace'])
 
     def convert_text(self, oeb_book):
         from calibre.ebooks.metadata.opf2 import OPF
diff --git a/src/calibre/ebooks/conversion/plugins/pml_input.py b/src/calibre/ebooks/conversion/plugins/pml_input.py
index 8bdb773358..d3db41f4f1 100644
--- a/src/calibre/ebooks/conversion/plugins/pml_input.py
+++ b/src/calibre/ebooks/conversion/plugins/pml_input.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
@@ -73,9 +74,9 @@ class PMLInput(InputFormatPlugin):
                 imgs = glob.glob(os.path.join(tdir, os.path.splitext(os.path.basename(stream.name))[0] + '_img', '*.png'))
         # No images in Dropbook location try generic images directory
         if not imgs:
-            imgs = glob.glob(os.path.join(os.path.join(tdir, u'images'), u'*.png'))
+            imgs = glob.glob(os.path.join(os.path.join(tdir, 'images'), '*.png'))
         if imgs:
-            os.makedirs(os.path.join(getcwd(), u'images'))
+            os.makedirs(os.path.join(getcwd(), 'images'))
         for img in imgs:
             pimg_name = os.path.basename(img)
             pimg_path = os.path.join(getcwd(), 'images', pimg_name)
@@ -99,11 +100,11 @@ class PMLInput(InputFormatPlugin):
 
         if file_ext == 'pmlz':
             log.debug('De-compressing content to temporary directory...')
-            with TemporaryDirectory(u'_unpmlz') as tdir:
+            with TemporaryDirectory('_unpmlz') as tdir:
                 zf = ZipFile(stream)
                 zf.extractall(tdir)
 
-                pmls = glob.glob(os.path.join(tdir, u'*.pml'))
+                pmls = glob.glob(os.path.join(tdir, '*.pml'))
                 for pml in pmls:
                     html_name = os.path.splitext(os.path.basename(pml))[0]+'.html'
                     html_path = os.path.join(getcwd(), html_name)
@@ -114,8 +115,8 @@ class PMLInput(InputFormatPlugin):
                     toc += ttoc
                 images = self.get_images(stream, tdir, True)
         else:
-            toc = self.process_pml(stream, u'index.html')
-            pages.append(u'index.html')
+            toc = self.process_pml(stream, 'index.html')
+            pages.append('index.html')
 
             if hasattr(stream, 'name'):
                 images = self.get_images(stream, os.path.abspath(os.path.dirname(stream.name)))
@@ -131,14 +132,14 @@ class PMLInput(InputFormatPlugin):
         log.debug('Reading metadata from input file...')
         mi = get_metadata(stream, 'pml')
         if 'images/cover.png' in images:
-            mi.cover = u'images/cover.png'
+            mi.cover = 'images/cover.png'
         opf = OPFCreator(getcwd(), mi)
         log.debug('Generating manifest...')
         opf.create_manifest(manifest_items)
         opf.create_spine(pages)
         opf.set_toc(toc)
-        with open(u'metadata.opf', 'wb') as opffile:
-            with open(u'toc.ncx', 'wb') as tocfile:
-                opf.render(opffile, tocfile, u'toc.ncx')
+        with open('metadata.opf', 'wb') as opffile:
+            with open('toc.ncx', 'wb') as tocfile:
+                opf.render(opffile, tocfile, 'toc.ncx')
 
-        return os.path.join(getcwd(), u'metadata.opf')
+        return os.path.join(getcwd(), 'metadata.opf')
diff --git a/src/calibre/ebooks/conversion/plugins/pml_output.py b/src/calibre/ebooks/conversion/plugins/pml_output.py
index 4f09bbbee1..0a42b074d2 100644
--- a/src/calibre/ebooks/conversion/plugins/pml_output.py
+++ b/src/calibre/ebooks/conversion/plugins/pml_output.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/rb_input.py b/src/calibre/ebooks/conversion/plugins/rb_input.py
index 3d7f93c192..f8a0377df5 100644
--- a/src/calibre/ebooks/conversion/plugins/rb_input.py
+++ b/src/calibre/ebooks/conversion/plugins/rb_input.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/rb_output.py b/src/calibre/ebooks/conversion/plugins/rb_output.py
index 01b1a4ef6d..7584609441 100644
--- a/src/calibre/ebooks/conversion/plugins/rb_output.py
+++ b/src/calibre/ebooks/conversion/plugins/rb_output.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/recipe_input.py b/src/calibre/ebooks/conversion/plugins/recipe_input.py
index 2670859e21..a3c2c8ce93 100644
--- a/src/calibre/ebooks/conversion/plugins/recipe_input.py
+++ b/src/calibre/ebooks/conversion/plugins/recipe_input.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>'
@@ -142,11 +142,11 @@ class RecipeInput(InputFormatPlugin):
         for key, val in self.recipe_object.conversion_options.items():
             setattr(opts, key, val)
 
-        for f in os.listdir(u'.'):
+        for f in os.listdir('.'):
             if f.endswith('.opf'):
                 return os.path.abspath(f)
 
-        for f in walk(u'.'):
+        for f in walk('.'):
             if f.endswith('.opf'):
                 return os.path.abspath(f)
 
diff --git a/src/calibre/ebooks/conversion/plugins/rtf_output.py b/src/calibre/ebooks/conversion/plugins/rtf_output.py
index 0e897ffd33..d74e567953 100644
--- a/src/calibre/ebooks/conversion/plugins/rtf_output.py
+++ b/src/calibre/ebooks/conversion/plugins/rtf_output.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/tcr_input.py b/src/calibre/ebooks/conversion/plugins/tcr_input.py
index 0578eb3aac..e996715f91 100644
--- a/src/calibre/ebooks/conversion/plugins/tcr_input.py
+++ b/src/calibre/ebooks/conversion/plugins/tcr_input.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/tcr_output.py b/src/calibre/ebooks/conversion/plugins/tcr_output.py
index 60672a65e0..9eb708672e 100644
--- a/src/calibre/ebooks/conversion/plugins/tcr_output.py
+++ b/src/calibre/ebooks/conversion/plugins/tcr_output.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plugins/txt_output.py b/src/calibre/ebooks/conversion/plugins/txt_output.py
index 0aced3cbf0..2dd9627bd6 100644
--- a/src/calibre/ebooks/conversion/plugins/txt_output.py
+++ b/src/calibre/ebooks/conversion/plugins/txt_output.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
 __copyright__ = '2009, John Schember <john@nachtimwald.com>'
diff --git a/src/calibre/ebooks/conversion/plumber.py b/src/calibre/ebooks/conversion/plumber.py
index a37a143750..a1da4ab2c2 100644
--- a/src/calibre/ebooks/conversion/plumber.py
+++ b/src/calibre/ebooks/conversion/plumber.py
@@ -1,4 +1,6 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__ = 'GPL 3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
@@ -848,7 +850,7 @@ OptionRecommendation(name='search_replace',
         rec = self.get_option_by_name(name)
         help = getattr(rec, 'help', None)
         if help is not None:
-            return help.replace('%default', str(rec.recommended_value))
+            return help.replace('%default', unicode_type(rec.recommended_value))
 
     def get_all_help(self):
         ans = {}
diff --git a/src/calibre/ebooks/conversion/preprocess.py b/src/calibre/ebooks/conversion/preprocess.py
index 11f3e1025e..c3ed86ce79 100644
--- a/src/calibre/ebooks/conversion/preprocess.py
+++ b/src/calibre/ebooks/conversion/preprocess.py
@@ -164,7 +164,7 @@ class DocAnalysis(object):
         for line in self.lines:
             l = len(line)
             if l > minLineLength and l < maxLineLength:
-                l = int(l/100)
+                l = int(l // 100)
                 # print("adding "+unicode_type(l))
                 hRaw[l]+=1