diff --git a/gns3/dialogs/appliance_wizard.py b/gns3/dialogs/appliance_wizard.py
index bb0aa00b..b4d3310a 100644
--- a/gns3/dialogs/appliance_wizard.py
+++ b/gns3/dialogs/appliance_wizard.py
@@ -18,10 +18,10 @@
 import os
 import sys
 
-from ..qt import QtWidgets, QtCore, QtWidgets, QtGui
+from ..qt import QtWidgets, QtCore, QtGui
 from ..ui.appliance_wizard_ui import Ui_ApplianceWizard
 from ..image_manager import ImageManager
-from ..registry.appliance import Appliance, ApplianceError
+from ..registry.appliance import Appliance
 from ..registry.registry import Registry
 from ..registry.config import Config, ConfigException
 from ..registry.image import Image
diff --git a/gns3/dialogs/symbol_selection_dialog.py b/gns3/dialogs/symbol_selection_dialog.py
index 780fd143..abf4c8d3 100644
--- a/gns3/dialogs/symbol_selection_dialog.py
+++ b/gns3/dialogs/symbol_selection_dialog.py
@@ -22,7 +22,6 @@ Dialog to change node symbols.
 import os
 
 from ..qt import QtSvg, QtCore, QtGui, QtWidgets
-from ..items.svg_node_item import SvgNodeItem
 from ..items.pixmap_node_item import PixmapNodeItem
 from ..ui.symbol_selection_dialog_ui import Ui_SymbolSelectionDialog
 from ..servers import Servers
@@ -55,22 +54,9 @@ class SymbolSelectionDialog(QtWidgets.QDialog, Ui_SymbolSelectionDialog):
         self._symbols_dir = QtCore.QStandardPaths.writableLocation(QtCore.QStandardPaths.PicturesLocation)
         self._symbols_path = Servers.instance().localServerSettings()["symbols_path"]
 
-        selected_symbol = symbol
         if not self._items:
             self.uiButtonBox.button(QtWidgets.QDialogButtonBox.Apply).hide()
-        else:
-            first_item = items[0]
-            if isinstance(first_item, SvgNodeItem):
-                custom_symbol = first_item.renderer().objectName()
-                if not custom_symbol:
-                    symbol_name = first_item.node().defaultSymbol()
-                else:
-                    symbol_name = custom_symbol
-                selected_symbol = symbol_name
-            elif isinstance(first_item, PixmapNodeItem):
-                selected_symbol = first_item.pixmapSymbolPath()
 
-        custom_symbol = True
         self.uiBuiltInSymbolRadioButton.setChecked(True)
         self.uiSymbolListWidget.setFocus()
         self.uiSymbolListWidget.setIconSize(QtCore.QSize(64, 64))
diff --git a/gns3/iouvm_converter.py b/gns3/iouvm_converter.py
index 1ab9b7ab..8eec94bb 100644
--- a/gns3/iouvm_converter.py
+++ b/gns3/iouvm_converter.py
@@ -18,14 +18,13 @@
 
 import sys
 import shutil
-import signal
 import json
 import os
 from datetime import datetime
 
 
 try:
-    from gns3.qt import QtCore, QtGui, QtWidgets, DEFAULT_BINDING
+    from gns3.qt import QtGui, QtWidgets
 except ImportError:
     raise SystemExit("Can't import Qt modules: Qt and/or PyQt is probably not installed correctly...")
 
@@ -128,7 +127,7 @@ class IOUVMConverterWizard(QtWidgets.QWizard, Ui_IOUVMConverterWizard):
                 topo = json.load(f)
             if "topology" in topo and "servers" in topo["topology"]:
                 for server in topo["topology"]["servers"]:
-                    if server["local"] == False:
+                    if server["local"] is False:
                         server["vm"] = True
                 with open(path, 'w+') as f:
                     topo = json.dump(topo, f)
diff --git a/gns3/local_server_config.py b/gns3/local_server_config.py
index b43b7158..06c99216 100644
--- a/gns3/local_server_config.py
+++ b/gns3/local_server_config.py
@@ -18,7 +18,6 @@
 import os
 import sys
 import configparser
-from gns3.qt import QtCore
 
 
 import logging
diff --git a/gns3/modules/builtin/pages/cloud_configuration_page.py b/gns3/modules/builtin/pages/cloud_configuration_page.py
index 05d95628..0052a040 100644
--- a/gns3/modules/builtin/pages/cloud_configuration_page.py
+++ b/gns3/modules/builtin/pages/cloud_configuration_page.py
@@ -20,7 +20,7 @@ Configuration page for clouds.
 """
 
 import re
-from gns3.qt import QtCore, QtGui, QtWidgets
+from gns3.qt import QtCore, QtWidgets
 from ..ui.cloud_configuration_page_ui import Ui_cloudConfigPageWidget
 
 
diff --git a/gns3/modules/dynamips/__init__.py b/gns3/modules/dynamips/__init__.py
index dcb56bc4..76bc9ed9 100644
--- a/gns3/modules/dynamips/__init__.py
+++ b/gns3/modules/dynamips/__init__.py
@@ -45,7 +45,6 @@ from .nodes.frame_relay_switch import FrameRelaySwitch
 from .nodes.atm_switch import ATMSwitch
 from .settings import DYNAMIPS_SETTINGS
 from .settings import IOS_ROUTER_SETTINGS
-from .settings import PLATFORMS_DEFAULT_RAM
 from .settings import DEFAULT_IDLEPC
 
 PLATFORM_TO_CLASS = {
@@ -374,7 +373,6 @@ class Dynamips(Module):
                                                            "IOS image", "IOS image {} could not be found\nPlease select an alternative from your existing images:".format(image),
                                                            list(candidate_ios_images.keys()), 0, False)
             if ok:
-                ios_image = candidate_ios_images[selection]  # FIXME
                 alternative_image["image"] = ios_router["image"]
                 alternative_image["ram"] = ios_router["ram"]
                 alternative_image["idlepc"] = ios_router["idlepc"]
diff --git a/gns3/modules/dynamips/pages/atm_bridge_configuration_page.py b/gns3/modules/dynamips/pages/atm_bridge_configuration_page.py
index e82b3237..f32a5d6a 100644
--- a/gns3/modules/dynamips/pages/atm_bridge_configuration_page.py
+++ b/gns3/modules/dynamips/pages/atm_bridge_configuration_page.py
@@ -20,7 +20,7 @@ Configuration page for Dynamips ATM bridges.
 """
 
 import re
-from gns3.qt import QtCore, QtGui, QtWidgets
+from gns3.qt import QtCore, QtWidgets
 from ..ui.atm_bridge_configuration_page_ui import Ui_atmBridgeConfigPageWidget
 
 
diff --git a/gns3/modules/dynamips/pages/atm_switch_configuration_page.py b/gns3/modules/dynamips/pages/atm_switch_configuration_page.py
index da21b987..e03266aa 100644
--- a/gns3/modules/dynamips/pages/atm_switch_configuration_page.py
+++ b/gns3/modules/dynamips/pages/atm_switch_configuration_page.py
@@ -20,7 +20,7 @@ Configuration page for Dynamips ATM switches.
 """
 
 import re
-from gns3.qt import QtCore, QtGui, QtWidgets
+from gns3.qt import QtCore, QtWidgets
 from ..ui.atm_switch_configuration_page_ui import Ui_atmSwitchConfigPageWidget
 
 
diff --git a/gns3/modules/dynamips/pages/ethernet_switch_configuration_page.py b/gns3/modules/dynamips/pages/ethernet_switch_configuration_page.py
index 81010165..4a44d27e 100644
--- a/gns3/modules/dynamips/pages/ethernet_switch_configuration_page.py
+++ b/gns3/modules/dynamips/pages/ethernet_switch_configuration_page.py
@@ -19,7 +19,7 @@
 Configuration page for Dynamips Ethernet switches.
 """
 
-from gns3.qt import QtCore, QtGui, QtWidgets
+from gns3.qt import QtCore, QtWidgets
 from ..utils.tree_widget_item import TreeWidgetItem
 from ..ui.ethernet_switch_configuration_page_ui import Ui_ethernetSwitchConfigPageWidget
 
diff --git a/gns3/modules/dynamips/pages/frame_relay_switch_configuration_page.py b/gns3/modules/dynamips/pages/frame_relay_switch_configuration_page.py
index 87a7dc6b..5aad6265 100644
--- a/gns3/modules/dynamips/pages/frame_relay_switch_configuration_page.py
+++ b/gns3/modules/dynamips/pages/frame_relay_switch_configuration_page.py
@@ -19,7 +19,7 @@
 Configuration page for Dynamips Frame Relay switches.
 """
 
-from gns3.qt import QtCore, QtGui, QtWidgets
+from gns3.qt import QtCore, QtWidgets
 from ..ui.frame_relay_switch_configuration_page_ui import Ui_frameRelaySwitchConfigPageWidget
 
 
diff --git a/gns3/modules/dynamips/pages/ios_router_preferences_page.py b/gns3/modules/dynamips/pages/ios_router_preferences_page.py
index 387bb226..803816c3 100644
--- a/gns3/modules/dynamips/pages/ios_router_preferences_page.py
+++ b/gns3/modules/dynamips/pages/ios_router_preferences_page.py
@@ -160,7 +160,6 @@ class IOSRouterPreferencesPage(QtWidgets.QWidget, Ui_IOSRouterPreferencesPageWid
         for item in self.uiIOSRoutersTreeWidget.selectedItems():
             if item:
                 key = item.data(0, QtCore.Qt.UserRole)
-                ios_router = self._ios_routers[key]
 
                 del self._ios_routers[key]
                 self.uiIOSRoutersTreeWidget.takeTopLevelItem(self.uiIOSRoutersTreeWidget.indexOfTopLevelItem(item))
diff --git a/gns3/modules/dynamips/utils/tree_widget_item.py b/gns3/modules/dynamips/utils/tree_widget_item.py
index 87e81ca9..21791559 100644
--- a/gns3/modules/dynamips/utils/tree_widget_item.py
+++ b/gns3/modules/dynamips/utils/tree_widget_item.py
@@ -15,7 +15,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from gns3.qt import QtGui, QtWidgets
+from gns3.qt import QtWidgets
 
 
 class TreeWidgetItem(QtWidgets.QTreeWidgetItem):
diff --git a/gns3/modules/iou/__init__.py b/gns3/modules/iou/__init__.py
index 01b0078f..22da3589 100644
--- a/gns3/modules/iou/__init__.py
+++ b/gns3/modules/iou/__init__.py
@@ -23,7 +23,7 @@ import sys
 import os
 import shutil
 
-from gns3.qt import QtCore, QtWidgets
+from gns3.qt import QtWidgets
 from gns3.local_server_config import LocalServerConfig
 from gns3.local_config import LocalConfig
 
diff --git a/gns3/modules/iou/iou_device.py b/gns3/modules/iou/iou_device.py
index 0bd1e24e..8d94f834 100644
--- a/gns3/modules/iou/iou_device.py
+++ b/gns3/modules/iou/iou_device.py
@@ -23,7 +23,6 @@ import os
 import re
 from gns3.vm import VM
 from gns3.node import Node
-from gns3.servers import Servers
 from gns3.packet_capture import PacketCapture
 from gns3.ports.ethernet_port import EthernetPort
 from gns3.ports.serial_port import SerialPort
diff --git a/gns3/modules/qemu/pages/qemu_vm_configuration_page.py b/gns3/modules/qemu/pages/qemu_vm_configuration_page.py
index f8920f17..1fad862c 100644
--- a/gns3/modules/qemu/pages/qemu_vm_configuration_page.py
+++ b/gns3/modules/qemu/pages/qemu_vm_configuration_page.py
@@ -21,7 +21,6 @@ Configuration page for QEMU VMs.
 
 import os
 import re
-import sip
 
 from collections import OrderedDict
 from gns3.modules.qemu.dialogs.qemu_image_wizard import QemuImageWizard
diff --git a/gns3/modules/virtualbox/dialogs/virtualbox_vm_wizard.py b/gns3/modules/virtualbox/dialogs/virtualbox_vm_wizard.py
index 8d4ca853..1144b234 100644
--- a/gns3/modules/virtualbox/dialogs/virtualbox_vm_wizard.py
+++ b/gns3/modules/virtualbox/dialogs/virtualbox_vm_wizard.py
@@ -19,8 +19,6 @@
 Wizard for VirtualBox VMs.
 """
 
-import sys
-
 from gns3.qt import QtGui, QtWidgets
 from gns3.servers import Servers
 from gns3.dialogs.vm_wizard import VMWizard
diff --git a/gns3/modules/vmware/dialogs/vmware_vm_wizard.py b/gns3/modules/vmware/dialogs/vmware_vm_wizard.py
index 23b7e4ca..900709a4 100644
--- a/gns3/modules/vmware/dialogs/vmware_vm_wizard.py
+++ b/gns3/modules/vmware/dialogs/vmware_vm_wizard.py
@@ -19,12 +19,9 @@
 Wizard for VMware VMs.
 """
 
-import sys
-
 from gns3.qt import QtGui, QtWidgets
 from gns3.servers import Servers
 from gns3.dialogs.vm_wizard import VMWizard
-from gns3.local_config import LocalConfig
 
 from ..ui.vmware_vm_wizard_ui import Ui_VMwareVMWizard
 from .. import VMware
diff --git a/gns3/modules/vmware/pages/vmware_vm_configuration_page.py b/gns3/modules/vmware/pages/vmware_vm_configuration_page.py
index ede76694..130bf599 100644
--- a/gns3/modules/vmware/pages/vmware_vm_configuration_page.py
+++ b/gns3/modules/vmware/pages/vmware_vm_configuration_page.py
@@ -19,8 +19,6 @@
 Configuration page for VMware VMs.
 """
 
-import sys
-
 from gns3.qt import QtGui, QtWidgets
 from gns3.dialogs.node_properties_dialog import ConfigurationError
 from gns3.dialogs.symbol_selection_dialog import SymbolSelectionDialog
diff --git a/gns3/modules/vpcs/pages/vpcs_device_configuration_page.py b/gns3/modules/vpcs/pages/vpcs_device_configuration_page.py
index 39901574..25666051 100644
--- a/gns3/modules/vpcs/pages/vpcs_device_configuration_page.py
+++ b/gns3/modules/vpcs/pages/vpcs_device_configuration_page.py
@@ -19,10 +19,7 @@
 Configuration page for VPCS devices.
 """
 
-import os
-
 from gns3.qt import QtWidgets
-from gns3.utils.get_resource import get_resource
 from ..ui.vpcs_device_configuration_page_ui import Ui_VPCSDeviceConfigPageWidget
 
 
diff --git a/gns3/pages/packet_capture_preferences_page.py b/gns3/pages/packet_capture_preferences_page.py
index 5369953e..9b738e1b 100644
--- a/gns3/pages/packet_capture_preferences_page.py
+++ b/gns3/pages/packet_capture_preferences_page.py
@@ -22,7 +22,7 @@ Configuration page for packet capture preferences.
 import sys
 import struct
 
-from gns3.qt import QtCore, QtGui, QtWidgets
+from gns3.qt import QtCore, QtWidgets
 from ..ui.packet_capture_preferences_page_ui import Ui_PacketCapturePreferencesPageWidget
 from ..settings import PACKET_CAPTURE_SETTINGS, PRECONFIGURED_PACKET_CAPTURE_READER_COMMANDS
 from ..ports.port import Port
diff --git a/gns3/registry/registry.py b/gns3/registry/registry.py
index 7a49b67e..9ebffa59 100644
--- a/gns3/registry/registry.py
+++ b/gns3/registry/registry.py
@@ -17,7 +17,6 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import os
-import copy
 
 import logging
 log = logging.getLogger(__name__)
diff --git a/gns3/update_manager.py b/gns3/update_manager.py
index 54cb2466..a88f2efe 100644
--- a/gns3/update_manager.py
+++ b/gns3/update_manager.py
@@ -196,7 +196,7 @@ class UpdateManager(QtCore.QObject):
                                                        QtWidgets.QMessageBox.Yes,
                                                        QtWidgets.QMessageBox.No)
                 if reply == QtWidgets.QMessageBox.Yes:
-                    app = QtWidgets.QApplication.instance().closeAllWindows()
+                    QtWidgets.QApplication.instance().closeAllWindows()
         else:
             log.debug('Error when downloading %s', file_path)
         network_reply.deleteLater()
@@ -210,7 +210,7 @@ class UpdateManager(QtCore.QObject):
         """
 
         if os.path.exists(self._update_directory):
-            package = os.makedirs(self._package_directory, exist_ok=True)
+            os.makedirs(self._package_directory, exist_ok=True)
 
             gui_tgz = os.path.join(self._update_directory, 'gns3-gui.tar.gz')
             self._extractTgz(gui_tgz)
diff --git a/gns3/utils/message_box.py b/gns3/utils/message_box.py
index e7310195..ab8ada4b 100644
--- a/gns3/utils/message_box.py
+++ b/gns3/utils/message_box.py
@@ -19,7 +19,7 @@
 To show a advanced message box.
 """
 
-from ..qt import QtGui, QtWidgets
+from ..qt import QtWidgets
 
 
 def MessageBox(parent, title, message, details="", icon=QtWidgets.QMessageBox.Critical):
diff --git a/scripts/build_pyqt.py b/scripts/build_pyqt.py
index b33a4d71..9c4fbda4 100755
--- a/scripts/build_pyqt.py
+++ b/scripts/build_pyqt.py
@@ -9,7 +9,6 @@ import sys
 import stat
 import shutil
 import subprocess
-import re
 import argparse
 
 parser = argparse.ArgumentParser()
diff --git a/tox.ini b/tox.ini
index 514065bf..f5975294 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,6 +9,10 @@ commands = py.test
 [pep8]
 ignore = E501,E402
 
+[flake8]
+ignore = E265,E501
+exclude = tests/*,gns3/ui/*,./gns3/modules/*/ui
+
 [pytest]
 python_paths = {toxinidir}
 norecursedirs = .tox