diff --git a/src/calibre/gui2/convert/bulk.py b/src/calibre/gui2/convert/bulk.py
index f825d4bd73..fd922604f8 100644
--- a/src/calibre/gui2/convert/bulk.py
+++ b/src/calibre/gui2/convert/bulk.py
@@ -21,7 +21,7 @@ from calibre.ebooks.conversion.plumber import Plumber
 from calibre.ebooks.conversion.config import sort_formats_by_preference, get_output_formats
 from calibre.utils.config import prefs
 from calibre.utils.logging import Log
-from polyglot.builtins import unicode_type
+from polyglot.builtins import unicode_type, native_string_type
 
 
 class BulkConfig(Config):
@@ -45,7 +45,7 @@ class BulkConfig(Config):
             'values saved in a previous conversion (if they exist) instead '
             'of using the defaults specified in the Preferences'))
 
-        self.output_formats.currentIndexChanged[str].connect(self.setup_pipeline)
+        self.output_formats.currentIndexChanged[native_string_type].connect(self.setup_pipeline)
         self.groups.setSpacing(5)
         self.groups.activated[(QModelIndex)].connect(self.show_pane)
         self.groups.clicked[(QModelIndex)].connect(self.show_pane)
diff --git a/src/calibre/gui2/convert/regex_builder.py b/src/calibre/gui2/convert/regex_builder.py
index 6a02384aa6..7e5874e358 100644
--- a/src/calibre/gui2/convert/regex_builder.py
+++ b/src/calibre/gui2/convert/regex_builder.py
@@ -18,7 +18,7 @@ from calibre.constants import iswindows
 from calibre.utils.ipc.simple_worker import fork_job, WorkerError
 from calibre.ebooks.conversion.search_replace import compile_regular_expression
 from calibre.ptempfile import TemporaryFile
-from polyglot.builtins import unicode_type, range
+from polyglot.builtins import unicode_type, range, native_string_type
 
 
 class RegexBuilder(QDialog, Ui_RegexBuilder):
@@ -42,7 +42,7 @@ class RegexBuilder(QDialog, Ui_RegexBuilder):
 
         self.cancelled = False
         self.button_box.accepted.connect(self.accept)
-        self.regex.textChanged[str].connect(self.regex_valid)
+        self.regex.textChanged[native_string_type].connect(self.regex_valid)
         for src, slot in (('test', 'do'), ('previous', 'goto'), ('next',
             'goto')):
             getattr(self, src).clicked.connect(getattr(self, '%s_%s'%(slot,
diff --git a/src/calibre/gui2/cover_flow.py b/src/calibre/gui2/cover_flow.py
index ec708602e2..a482b3e3a3 100644
--- a/src/calibre/gui2/cover_flow.py
+++ b/src/calibre/gui2/cover_flow.py
@@ -12,7 +12,7 @@ Module to implement the Cover Flow feature
 import sys, os, time
 
 from PyQt5.Qt import (QImage, QSizePolicy, QTimer, QDialog, Qt, QSize, QAction,
-        QStackedLayout, QLabel, QByteArray, pyqtSignal, QKeySequence, QFont)
+        QStackedLayout, QLabel, pyqtSignal, QKeySequence, QFont)
 
 from calibre import plugins
 from calibre.ebooks.metadata import rating_to_stars
@@ -242,9 +242,8 @@ class CBDialog(QDialog):
         self.setWindowTitle(_('Browse by covers'))
         self.layout().addWidget(cover_flow)
 
-        geom = gprefs.get('cover_browser_dialog_geometry', bytearray(''))
-        geom = QByteArray(geom)
-        if not self.restoreGeometry(geom):
+        geom = gprefs.get('cover_browser_dialog_geometry', None)
+        if not geom or not self.restoreGeometry(geom):
             h, w = available_height()-60, int(available_width()/1.5)
             self.resize(w, h)
         self.action_fs_toggle = a = QAction(self)
diff --git a/src/calibre/gui2/dialogs/catalog.py b/src/calibre/gui2/dialogs/catalog.py
index 25a3d2a3ac..6230b0b4c8 100644
--- a/src/calibre/gui2/dialogs/catalog.py
+++ b/src/calibre/gui2/dialogs/catalog.py
@@ -22,7 +22,7 @@ class Catalog(QDialog, Ui_Dialog):
     ''' Catalog Dialog builder'''
 
     def __init__(self, parent, dbspec, ids, db):
-        import re, io
+        import re
         from calibre import prints as info
         from PyQt5.uic import compileUi
 
@@ -67,13 +67,14 @@ class Catalog(QDialog, Ui_Dialog):
 
                     # Compile the .ui form provided in plugin.zip
                     if not os.path.exists(compiled_form):
+                        from polyglot.io import PolyglotStringIO
                         # info('\tCompiling form', form)
-                        buf = io.BytesIO()
+                        buf = PolyglotStringIO()
                         compileUi(form, buf)
                         dat = buf.getvalue()
                         dat = re.compile(r'QtGui.QApplication.translate\(.+?,\s+"(.+?)(?<!\\)",.+?\)',
                                          re.DOTALL).sub(r'_("\1")', dat)
-                        open(compiled_form, 'wb').write(dat)
+                        open(compiled_form, 'wb').write(dat.encode('utf-8'))
 
                     # Import the dynamic PluginWidget() from .py file provided in plugin.zip
                     try:
@@ -181,7 +182,7 @@ class Catalog(QDialog, Ui_Dialog):
         When title/format change, invalidate Preset in E-book options tab
         '''
         cf = unicode_type(self.format.currentText()).lower()
-        if cf in ['azw3', 'epub', 'mobi'] and hasattr(self.options_widget, 'settings_changed'):
+        if cf in ('azw3', 'epub', 'mobi') and hasattr(self.options_widget, 'settings_changed'):
             self.options_widget.settings_changed("title/format")
 
     @property
diff --git a/src/calibre/gui2/dialogs/edit_authors_dialog.py b/src/calibre/gui2/dialogs/edit_authors_dialog.py
index 5517e8ca00..b520bef2cb 100644
--- a/src/calibre/gui2/dialogs/edit_authors_dialog.py
+++ b/src/calibre/gui2/dialogs/edit_authors_dialog.py
@@ -39,9 +39,10 @@ class EditAuthorsDialog(QDialog, Ui_EditAuthorsDialog):
         try:
             self.table_column_widths = \
                         gprefs.get('manage_authors_table_widths', None)
-            geom = gprefs.get('manage_authors_dialog_geometry', bytearray(''))
-            self.restoreGeometry(QByteArray(geom))
-        except:
+            geom = gprefs.get('manage_authors_dialog_geometry', None)
+            if geom:
+                self.restoreGeometry(QByteArray(geom))
+        except Exception:
             pass
 
         self.buttonBox.button(QDialogButtonBox.Ok).setText(_('&OK'))
@@ -159,7 +160,7 @@ class EditAuthorsDialog(QDialog, Ui_EditAuthorsDialog):
             # have a width. Assume 25. Not a problem because user-changed column
             # widths will be remembered
             w = self.table.width() - 25 - self.table.verticalHeader().width()
-            w /= self.table.columnCount()
+            w //= self.table.columnCount()
             for c in range(0, self.table.columnCount()):
                 self.table.setColumnWidth(c, w)
         self.save_state()
diff --git a/src/calibre/gui2/dialogs/match_books.py b/src/calibre/gui2/dialogs/match_books.py
index b97d8fcddb..d1148c0f0b 100644
--- a/src/calibre/gui2/dialogs/match_books.py
+++ b/src/calibre/gui2/dialogs/match_books.py
@@ -58,8 +58,9 @@ class MatchBooks(QDialog, Ui_MatchBooks):
         try:
             self.books_table_column_widths = \
                         gprefs.get('match_books_dialog_books_table_widths', None)
-            geom = gprefs.get('match_books_dialog_geometry', bytearray(''))
-            self.restoreGeometry(QByteArray(geom))
+            geom = gprefs.get('match_books_dialog_geometry', None)
+            if geom:
+                self.restoreGeometry(QByteArray(geom))
         except:
             pass
 
diff --git a/src/calibre/gui2/dialogs/quickview.py b/src/calibre/gui2/dialogs/quickview.py
index 35dbf8d9f2..d4e51817b7 100644
--- a/src/calibre/gui2/dialogs/quickview.py
+++ b/src/calibre/gui2/dialogs/quickview.py
@@ -155,8 +155,9 @@ class Quickview(QDialog, Ui_Quickview):
             self.books_table_column_widths = \
                         gprefs.get('quickview_dialog_books_table_widths', None)
             if not self.is_pane:
-                geom = gprefs.get('quickview_dialog_geometry', bytearray(''))
-                self.restoreGeometry(QByteArray(geom))
+                geom = gprefs.get('quickview_dialog_geometry', None)
+                if geom:
+                    self.restoreGeometry(QByteArray(geom))
         except:
             pass
 
@@ -588,7 +589,7 @@ class Quickview(QDialog, Ui_Quickview):
             # have a width. Assume 25. Not a problem because user-changed column
             # widths will be remembered
             w = self.books_table.width() - 25 - self.books_table.verticalHeader().width()
-            w /= self.books_table.columnCount()
+            w //= self.books_table.columnCount()
             for c in range(0, self.books_table.columnCount()):
                 self.books_table.setColumnWidth(c, w)
         self.save_state()
diff --git a/src/calibre/gui2/jobs.py b/src/calibre/gui2/jobs.py
index 5431794ed9..b08cdf3f89 100644
--- a/src/calibre/gui2/jobs.py
+++ b/src/calibre/gui2/jobs.py
@@ -643,8 +643,9 @@ class JobsDialog(QDialog, Ui_JobsDialog):
 
     def restore_state(self):
         try:
-            geom = gprefs.get('jobs_dialog_geometry', bytearray(''))
-            self.restoreGeometry(QByteArray(geom))
+            geom = gprefs.get('jobs_dialog_geometry', None)
+            if geom:
+                self.restoreGeometry(QByteArray(geom))
             state = gprefs.get('jobs view column layout3', None)
             if state is not None:
                 self.jobs_view.horizontalHeader().restoreState(QByteArray(state))