diff --git a/src/calibre/gui2/dialogs/device_category_editor.py b/src/calibre/gui2/dialogs/device_category_editor.py
index 38f17849ae..61069abf2e 100644
--- a/src/calibre/gui2/dialogs/device_category_editor.py
+++ b/src/calibre/gui2/dialogs/device_category_editor.py
@@ -60,7 +60,7 @@ class DeviceCategoryEditor(QDialog, Ui_DeviceCategoryEditor):
         self.setWindowIcon(icon)
 
         self.to_rename = {}
-        self.to_delete = set([])
+        self.to_delete = set()
         self.original_names = {}
         self.all_tags = {}
 
diff --git a/src/calibre/gui2/dialogs/scheduler.py b/src/calibre/gui2/dialogs/scheduler.py
index b7d50f2c52..e5c14ca357 100644
--- a/src/calibre/gui2/dialogs/scheduler.py
+++ b/src/calibre/gui2/dialogs/scheduler.py
@@ -587,7 +587,7 @@ class Scheduler(QObject):
         self.recipe_model = RecipeModel()
         self.db = db
         self.lock = QMutex(QMutex.Recursive)
-        self.download_queue = set([])
+        self.download_queue = set()
 
         self.news_menu = QMenu()
         self.news_icon = QIcon(I('news.png'))
diff --git a/src/calibre/gui2/dialogs/select_formats.py b/src/calibre/gui2/dialogs/select_formats.py
index 6d4038cc41..8fb53c015c 100644
--- a/src/calibre/gui2/dialogs/select_formats.py
+++ b/src/calibre/gui2/dialogs/select_formats.py
@@ -81,7 +81,7 @@ class SelectFormats(QDialog):
         self.fview.setSpacing(2)
 
         self.resize(350, 500)
-        self.selected_formats = set([])
+        self.selected_formats = set()
 
     def accept(self, *args):
         for idx in self.fview.selectedIndexes():