diff --git a/src/calibre/gui2/preferences/behavior.py b/src/calibre/gui2/preferences/behavior.py
index fdc1b4499d..9ff97c99e1 100644
--- a/src/calibre/gui2/preferences/behavior.py
+++ b/src/calibre/gui2/preferences/behavior.py
@@ -108,7 +108,7 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
             fmts = config['internally_viewed_formats']
         viewer = self.opt_internally_viewed_formats
         viewer.blockSignals(True)
-        exts = set([])
+        exts = set()
         for ext in BOOK_EXTENSIONS:
             ext = ext.lower()
             ext = re.sub(r'(x{0,1})htm(l{0,1})', 'html', ext)
diff --git a/src/calibre/gui2/preferences/misc.py b/src/calibre/gui2/preferences/misc.py
index e7dbd1867f..617d6a64ff 100644
--- a/src/calibre/gui2/preferences/misc.py
+++ b/src/calibre/gui2/preferences/misc.py
@@ -9,7 +9,7 @@ import textwrap
 
 from calibre.gui2.preferences import ConfigWidgetBase, test_widget, Setting
 from calibre.gui2.preferences.misc_ui import Ui_Form
-from calibre.gui2 import (config, open_local_file, gprefs)
+from calibre.gui2 import config, open_local_file, gprefs
 from calibre import get_proxies
 from polyglot.builtins import iteritems
 
diff --git a/src/calibre/gui2/preferences/plugins.py b/src/calibre/gui2/preferences/plugins.py
index c3c777f1e9..21c53f0e7e 100644
--- a/src/calibre/gui2/preferences/plugins.py
+++ b/src/calibre/gui2/preferences/plugins.py
@@ -64,7 +64,7 @@ class PluginModel(QAbstractItemModel, AdaptSQP):  # {{{
             plugins.sort(key=lambda x: x.name.lower())
 
     def universal_set(self):
-        ans = set([])
+        ans = set()
         for c, category in enumerate(self.categories):
             ans.add((c, -1))
             for p, plugin in enumerate(self._data[category]):
@@ -74,7 +74,7 @@ class PluginModel(QAbstractItemModel, AdaptSQP):  # {{{
     def get_matches(self, location, query, candidates=None):
         if candidates is None:
             candidates = self.universal_set()
-        ans = set([])
+        ans = set()
         if not query:
             return ans
         query = lower(query)
diff --git a/src/calibre/gui2/preferences/toolbar.py b/src/calibre/gui2/preferences/toolbar.py
index c1bbad6a45..eec30a2859 100644
--- a/src/calibre/gui2/preferences/toolbar.py
+++ b/src/calibre/gui2/preferences/toolbar.py
@@ -22,13 +22,13 @@ def sort_key_for_action(ac):
         q = ac.name if q is None else q[0]
         return primary_sort_key(force_unicode(q))
     except Exception:
-        return primary_sort_key(u'')
+        return primary_sort_key('')
 
 
 class FakeAction(object):
 
     def __init__(self, name, gui_name, icon, tooltip=None,
-            dont_add_to=frozenset([]), dont_remove_from=frozenset([])):
+            dont_add_to=frozenset(), dont_remove_from=frozenset()):
         self.name = name
         self.action_spec = (gui_name, icon, tooltip, None)
         self.dont_remove_from = dont_remove_from
@@ -131,7 +131,7 @@ class AllModel(BaseModel):
 
     def remove(self, indices, allowed):
         rows = [i.row() for i in indices]
-        remove = set([])
+        remove = set()
         for row in rows:
             ac = self._data[row]
             if ac.name.startswith('---'):
@@ -181,7 +181,7 @@ class CurrentModel(BaseModel):
 
     def add(self, names):
         actions = []
-        reject = set([])
+        reject = set()
         for name in names:
             ac = self.name_to_action(name, self.gui)
             if self.key in ac.dont_add_to:
@@ -196,7 +196,7 @@ class CurrentModel(BaseModel):
 
     def remove(self, indices):
         rows = [i.row() for i in indices]
-        remove, rejected = set([]), set([])
+        remove, rejected = set(), set()
         for row in rows:
             ac = self._data[row]
             if self.key in ac.dont_remove_from:
diff --git a/src/calibre/gui2/wizard/__init__.py b/src/calibre/gui2/wizard/__init__.py
index 8f4a4472d5..abb00ecece 100644
--- a/src/calibre/gui2/wizard/__init__.py
+++ b/src/calibre/gui2/wizard/__init__.py
@@ -417,7 +417,7 @@ def get_devices():
 
 
 def get_manufacturers():
-    mans = set([])
+    mans = set()
     for x in get_devices():
         mans.add(x.manufacturer)
     if Device.manufacturer in mans:
diff --git a/src/calibre/library/custom_columns.py b/src/calibre/library/custom_columns.py
index 80e25f9e3b..1d73744a06 100644
--- a/src/calibre/library/custom_columns.py
+++ b/src/calibre/library/custom_columns.py
@@ -536,7 +536,7 @@ class CustomColumns(object):
         if num is not None:
             data = self.custom_column_num_map[num]
         if data['datatype'] == 'composite':
-            return set([])
+            return set()
         if not data['editable']:
             raise ValueError('Column %r is not editable'%data['label'])
         table, lt = self.custom_table_names(data['num'])
@@ -549,7 +549,7 @@ class CustomColumns(object):
             if extra is None:
                 extra = 1.0
 
-        books_to_refresh = set([])
+        books_to_refresh = set()
         if data['normalized']:
             if data['datatype'] == 'enumeration' and (
                     val and val not in data['display']['enum_values']):
@@ -563,7 +563,7 @@ class CustomColumns(object):
             set_val = val if data['is_multiple'] else [val]
             existing = getter()
             if not existing:
-                existing = set([])
+                existing = set()
             else:
                 existing = set(existing)
             # preserve the order in set_val