diff --git a/src/calibre/db/backend.py b/src/calibre/db/backend.py
index 27d0c09d52..8800b47885 100644
--- a/src/calibre/db/backend.py
+++ b/src/calibre/db/backend.py
@@ -152,8 +152,11 @@ class DBPrefs(dict):  # {{{
     def write_serialized(self, library_path):
         try:
             to_filename = os.path.join(library_path, 'metadata_db_prefs_backup.json')
+            data = json.dumps(self, indent=2, default=to_json)
+            if not isinstance(data, bytes):
+                data = data.encode('utf-8')
             with open(to_filename, "wb") as f:
-                f.write(json.dumps(self, indent=2, default=to_json))
+                f.write(data)
         except:
             import traceback
             traceback.print_exc()
diff --git a/src/calibre/db/categories.py b/src/calibre/db/categories.py
index cc6ea00dd8..d073a2d5f1 100644
--- a/src/calibre/db/categories.py
+++ b/src/calibre/db/categories.py
@@ -75,7 +75,7 @@ class Tag(object):
 
 
 def find_categories(field_metadata):
-    for category, cat in iteritems(field_metadata):
+    for category, cat in field_metadata.iter_items():
         if (cat['is_category'] and cat['kind'] not in {'user', 'search'}):
             yield (category, cat['is_multiple'].get('cache_to_list', None), False)
         elif (cat['datatype'] == 'composite' and
diff --git a/src/calibre/db/search.py b/src/calibre/db/search.py
index 594ffde15c..7463a11ef9 100644
--- a/src/calibre/db/search.py
+++ b/src/calibre/db/search.py
@@ -632,7 +632,7 @@ class Parser(SearchQueryParser):  # {{{
         text_fields = set()
         field_metadata = {}
 
-        for x, fm in iteritems(self.field_metadata):
+        for x, fm in self.field_metadata.iter_items():
             if x.startswith('@'):
                 continue
             if fm['search_terms'] and x not in {'series_sort', 'id'}:
diff --git a/src/calibre/devices/usbms/driver.py b/src/calibre/devices/usbms/driver.py
index c475800ab3..22aa18a6b5 100644
--- a/src/calibre/devices/usbms/driver.py
+++ b/src/calibre/devices/usbms/driver.py
@@ -128,13 +128,19 @@ class USBMS(CLI, Device):
                     driveinfo = None
                 driveinfo = self._update_driveinfo_record(driveinfo, prefix,
                                                           location_code, name)
+            data = json.dumps(driveinfo, default=to_json)
+            if not isinstance(data, bytes):
+                data = data.encode('utf-8')
             with lopen(os.path.join(prefix, self.DRIVEINFO), 'wb') as f:
-                f.write(json.dumps(driveinfo, default=to_json))
+                f.write(data)
                 fsync(f)
         else:
             driveinfo = self._update_driveinfo_record({}, prefix, location_code, name)
+            data = json.dumps(driveinfo, default=to_json)
+            if not isinstance(data, bytes):
+                data = data.encode('utf-8')
             with lopen(os.path.join(prefix, self.DRIVEINFO), 'wb') as f:
-                f.write(json.dumps(driveinfo, default=to_json))
+                f.write(data)
                 fsync(f)
         return driveinfo
 
diff --git a/src/calibre/ebooks/metadata/book/json_codec.py b/src/calibre/ebooks/metadata/book/json_codec.py
index 46027c03c0..8bef9a9e25 100644
--- a/src/calibre/ebooks/metadata/book/json_codec.py
+++ b/src/calibre/ebooks/metadata/book/json_codec.py
@@ -132,8 +132,10 @@ class JsonCodec(object):
         self.field_metadata = field_metadata or FieldMetadata()
 
     def encode_to_file(self, file_, booklist):
-        file_.write(json.dumps(self.encode_booklist_metadata(booklist),
-                              indent=2, encoding='utf-8'))
+        data = json.dumps(self.encode_booklist_metadata(booklist), indent=2, encoding='utf-8')
+        if not isinstance(data, bytes):
+            data = data.encode('utf-8')
+        file_.write(data)
 
     def encode_booklist_metadata(self, booklist):
         result = []
diff --git a/src/calibre/gui2/dialogs/plugin_updater.py b/src/calibre/gui2/dialogs/plugin_updater.py
index cfcddde0e1..b3a09de848 100644
--- a/src/calibre/gui2/dialogs/plugin_updater.py
+++ b/src/calibre/gui2/dialogs/plugin_updater.py
@@ -45,7 +45,7 @@ def get_plugin_updates_available(raise_error=False):
         return None
     display_plugins = read_available_plugins(raise_error=raise_error)
     if display_plugins:
-        update_plugins = filter(filter_upgradeable_plugins, display_plugins)
+        update_plugins = list(filter(filter_upgradeable_plugins, display_plugins))
         if len(update_plugins) > 0:
             return update_plugins
     return None
@@ -589,7 +589,7 @@ class PluginUpdaterDialog(SizePersistedDialog):
 
     def _finished(self, *args):
         if self.model:
-            update_plugins = filter(filter_upgradeable_plugins, self.model.display_plugins)
+            update_plugins = list(filter(filter_upgradeable_plugins, self.model.display_plugins))
             self.gui.recalc_update_label(len(update_plugins))
 
     def _plugin_current_changed(self, current, previous):
diff --git a/src/calibre/gui2/dialogs/search.py b/src/calibre/gui2/dialogs/search.py
index 0a3ebd278a..b764b09ad3 100644
--- a/src/calibre/gui2/dialogs/search.py
+++ b/src/calibre/gui2/dialogs/search.py
@@ -19,7 +19,7 @@ from calibre.utils.icu import sort_key
 from calibre.utils.config import tweaks
 from calibre.utils.date import now
 from calibre.utils.localization import localize_user_manual_link
-from polyglot.builtins import iteritems, unicode_type, range
+from polyglot.builtins import unicode_type, range
 
 box_values = {}
 last_matchkind = CONTAINS_MATCH
@@ -174,7 +174,7 @@ def create_date_tab(self, db):
     w.h1 = h = QHBoxLayout()
     l.addLayout(h)
     self.date_field = df = add(_("&Search the"), QComboBox(w))
-    vals = [((v['search_terms'] or [k])[0], v['name'] or k) for k, v in iteritems(db.field_metadata) if v.get('datatype', None) == 'datetime']
+    vals = [((v['search_terms'] or [k])[0], v['name'] or k) for k, v in db.field_metadata.iter_items() if v.get('datatype', None) == 'datetime']
     for k, v in sorted(vals, key=lambda k_v: sort_key(k_v[1])):
         df.addItem(v, k)
     h.addWidget(df)
diff --git a/src/calibre/gui2/library/delegates.py b/src/calibre/gui2/library/delegates.py
index 7c91eaec3b..b5192b280f 100644
--- a/src/calibre/gui2/library/delegates.py
+++ b/src/calibre/gui2/library/delegates.py
@@ -202,7 +202,7 @@ def get_val_for_textlike_columns(index_):
 class RatingDelegate(QStyledItemDelegate, UpdateEditorGeometry):  # {{{
 
     def __init__(self, *args, **kwargs):
-        QStyledItemDelegate.__init__(self, *args, **kwargs)
+        QStyledItemDelegate.__init__(self, *args)
         self.is_half_star = kwargs.get('is_half_star', False)
         self.table_widget = args[0]
         self.rf = QFont(rating_font())
diff --git a/src/calibre/gui2/preferences/coloring.py b/src/calibre/gui2/preferences/coloring.py
index 43aa34edd1..96216b7bf7 100644
--- a/src/calibre/gui2/preferences/coloring.py
+++ b/src/calibre/gui2/preferences/coloring.py
@@ -1090,8 +1090,11 @@ class EditRules(QWidget):  # {{{
                 'type': self.model.pref_name,
                 'rules': self.model.rules_as_list(for_export=True)
             }
+            data = json.dumps(rules, indent=2)
+            if not isinstance(data, bytes):
+                data = data.encode('utf-8')
             with lopen(path, 'wb') as f:
-                f.write(json.dumps(rules, indent=2))
+                f.write(data)
 
     def import_rules(self):
         files = choose_files(self, 'import-coloring-rules', _('Choose file to import from'),
diff --git a/src/calibre/gui2/threaded_jobs.py b/src/calibre/gui2/threaded_jobs.py
index aef553133d..e58808993d 100644
--- a/src/calibre/gui2/threaded_jobs.py
+++ b/src/calibre/gui2/threaded_jobs.py
@@ -129,9 +129,11 @@ class ThreadedJob(BaseJob):
         if not os.path.exists(log_dir):
             os.makedirs(log_dir)
         fd, path = tempfile.mkstemp(suffix='.json', prefix='log-', dir=log_dir)
+        data = json.dumps(logs, ensure_ascii=False, indent=2)
+        if not isinstance(data, bytes):
+            data = data.encode('utf-8')
         with os.fdopen(fd, 'wb') as f:
-            f.write(json.dumps(logs, ensure_ascii=False,
-                indent=2).encode('utf-8'))
+            f.write(data)
         self.consolidated_log = path
         self.log = None
 
diff --git a/src/calibre/gui2/viewer/bookmarkmanager.py b/src/calibre/gui2/viewer/bookmarkmanager.py
index 3b81f80eaf..2452c9e678 100644
--- a/src/calibre/gui2/viewer/bookmarkmanager.py
+++ b/src/calibre/gui2/viewer/bookmarkmanager.py
@@ -200,8 +200,11 @@ class BookmarkManager(QWidget):
             self, 'export-viewer-bookmarks', _('Export bookmarks'),
             filters=[(_('Saved bookmarks'), ['calibre-bookmarks'])], all_files=False, initial_filename='bookmarks.calibre-bookmarks')
         if filename:
+            data = json.dumps(self.get_bookmarks(), indent=True)
+            if not isinstance(data, bytes):
+                data = data.encode('utf-8')
             with lopen(filename, 'wb') as fileobj:
-                fileobj.write(json.dumps(self.get_bookmarks(), indent=True))
+                fileobj.write(data)
 
     def import_bookmarks(self):
         files = choose_files(self, 'export-viewer-bookmarks', _('Import bookmarks'),
diff --git a/src/calibre/library/field_metadata.py b/src/calibre/library/field_metadata.py
index 523f322521..27a6d29d6f 100644
--- a/src/calibre/library/field_metadata.py
+++ b/src/calibre/library/field_metadata.py
@@ -493,13 +493,14 @@ class FieldMetadata(object):
     def iteritems(self):
         for key in self._tb_cats:
             yield (key, self._tb_cats[key])
+    iter_items = iteritems
 
     def custom_iteritems(self):
         for key, meta in iteritems(self._tb_custom_fields):
             yield (key, meta)
 
     def items(self):
-        return list(iteritems(self))
+        return list(self.iter_items())
 
     def is_custom_field(self, key):
         return key.startswith(self.custom_field_prefix)
diff --git a/src/calibre/library/prefs.py b/src/calibre/library/prefs.py
index 3c41a4d78f..9ef2214da8 100644
--- a/src/calibre/library/prefs.py
+++ b/src/calibre/library/prefs.py
@@ -81,8 +81,11 @@ class DBPrefs(dict):
     def write_serialized(self, library_path):
         try:
             to_filename = os.path.join(library_path, 'metadata_db_prefs_backup.json')
+            data = json.dumps(self, indent=2, default=to_json)
+            if not isinstance(data, bytes):
+                data = data.encode('utf-8')
             with open(to_filename, "wb") as f:
-                f.write(json.dumps(self, indent=2, default=to_json))
+                f.write(data)
         except:
             import traceback
             traceback.print_exc()
diff --git a/src/calibre/srv/render_book.py b/src/calibre/srv/render_book.py
index 1bac7c4082..407c457889 100644
--- a/src/calibre/srv/render_book.py
+++ b/src/calibre/srv/render_book.py
@@ -230,8 +230,11 @@ class Container(ContainerBase):
         self.commit()
         for name in excluded_names:
             os.remove(self.name_path_map[name])
+        data = json.dumps(self.book_render_data, ensure_ascii=False)
+        if not isinstance(data, bytes):
+            data = data.encode('utf-8')
         with lopen(os.path.join(self.root, 'calibre-book-manifest.json'), 'wb') as f:
-            f.write(json.dumps(self.book_render_data, ensure_ascii=False).encode('utf-8'))
+            f.write(data)
 
     def create_cover_page(self, input_fmt):
         templ = '''