diff --git a/picard/acoustid.py b/picard/acoustid.py
index 2d7b526f1..c50c7e532 100644
--- a/picard/acoustid.py
+++ b/picard/acoustid.py
@@ -21,7 +21,7 @@ from collections import deque
 from functools import partial
 from PyQt4 import QtCore
 from picard import config, log
-from picard.const import ACOUSTID_KEY, FPCALC_NAMES
+from picard.const import FPCALC_NAMES
 from picard.util import find_executable
 from picard.webservice import XmlNode
 
diff --git a/picard/cluster.py b/picard/cluster.py
index c14e47818..ad718dc47 100644
--- a/picard/cluster.py
+++ b/picard/cluster.py
@@ -24,10 +24,9 @@ from heapq import heappush, heappop
 from PyQt4 import QtCore
 from picard import config
 from picard.metadata import Metadata
-from picard.similarity import similarity2, similarity
+from picard.similarity import similarity
 from picard.ui.item import Item
 from picard.util import format_time
-from picard.mbxml import artist_credit_from_node
 
 
 class Cluster(QtCore.QObject, Item):
@@ -190,10 +189,10 @@ class Cluster(QtCore.QObject, Item):
                            albumDict.add(album)))
 
         artist_cluster_engine = ClusterEngine(artistDict)
-        artist_cluster = artist_cluster_engine.cluster(threshold)
+        artist_cluster_engine.cluster(threshold)
 
         album_cluster_engine = ClusterEngine(albumDict)
-        album_cluster = album_cluster_engine.cluster(threshold)
+        album_cluster_engine.cluster(threshold)
 
         # Arrange tracks into albums
         albums = {}
@@ -459,7 +458,5 @@ class ClusterEngine(object):
                     self.idClusterIndex[match] = match0
                 del self.clusterBins[match1]
 
-        return self.clusterBins
-
     def can_refresh(self):
         return False
diff --git a/picard/config.py b/picard/config.py
index 5a4f8c176..983091980 100644
--- a/picard/config.py
+++ b/picard/config.py
@@ -20,7 +20,7 @@
 from operator import itemgetter
 from PyQt4 import QtCore
 from picard import (PICARD_APP_NAME, PICARD_ORG_NAME, PICARD_VERSION,
-                    version_to_string, version_from_string, log)
+                    version_to_string, version_from_string)
 from picard.util import LockableObject, rot13
 
 
diff --git a/picard/const.py b/picard/const.py
index 31152db57..68af4f98b 100644
--- a/picard/const.py
+++ b/picard/const.py
@@ -19,7 +19,6 @@
 
 import os
 import sys
-import re
 
 # Install gettext "noop" function in case const.py gets imported directly.
 import __builtin__
diff --git a/picard/coverart.py b/picard/coverart.py
index df5cac28d..a71264f0f 100644
--- a/picard/coverart.py
+++ b/picard/coverart.py
@@ -24,10 +24,9 @@
 import json
 import re
 import traceback
-import picard.webservice
 from functools import partial
 from picard import config, log
-from picard.metadata import Metadata, is_front_image
+from picard.metadata import is_front_image
 from picard.util import mimetype, parse_amazon_url
 from picard.const import CAA_HOST, CAA_PORT
 from PyQt4.QtCore import QUrl, QObject
diff --git a/picard/file.py b/picard/file.py
index 3536ddce6..9a4b77c45 100644
--- a/picard/file.py
+++ b/picard/file.py
@@ -29,11 +29,9 @@ from operator import itemgetter
 from collections import defaultdict
 from PyQt4 import QtCore
 from picard import config, log
-from picard.track import Track
 from picard.metadata import Metadata
 from picard.ui.item import Item
 from picard.script import ScriptParser
-from picard.similarity import similarity2
 from picard.util import (
     decode_filename,
     encode_filename,
@@ -144,7 +142,7 @@ class File(QtCore.QObject, Item):
     def has_error(self):
         return self.state == File.ERROR
 
-    def _load(self):
+    def _load(self, filename):
         """Load metadata from the file."""
         raise NotImplementedError
 
@@ -359,8 +357,8 @@ class File(QtCore.QObject, Item):
                 # image multiple times
                 if (os.path.exists(new_filename) and
                     os.path.getsize(new_filename) == len(data)):
-                        log.debug("Identical file size, not saving %r", image_filename)
-                        continue
+                    log.debug("Identical file size, not saving %r", image_filename)
+                    continue
                 log.debug("Saving cover images to %r", image_filename)
                 new_dirname = os.path.dirname(image_filename)
                 if not os.path.isdir(new_dirname):
diff --git a/picard/formats/mutagenext/compatid3.py b/picard/formats/mutagenext/compatid3.py
index aa3612645..a3098c5eb 100644
--- a/picard/formats/mutagenext/compatid3.py
+++ b/picard/formats/mutagenext/compatid3.py
@@ -22,7 +22,7 @@ import struct
 from struct import pack, unpack
 import mutagen
 from mutagen._util import insert_bytes
-from mutagen.id3 import ID3, Frame, Frames, Frames_2_2, TextFrame, TORY, \
+from mutagen.id3 import ID3, Frames, Frames_2_2, TextFrame, TORY, \
     TYER, TIME, APIC, IPLS, TDAT, BitPaddedInt, MakeID3v1
 
 
diff --git a/picard/i18n.py b/picard/i18n.py
index 8520ee252..03b61850e 100644
--- a/picard/i18n.py
+++ b/picard/i18n.py
@@ -1,3 +1,22 @@
+# -*- coding: utf-8 -*-
+#
+# Picard, the next-generation MusicBrainz tagger
+# Copyright (C) 2013 Laurent Monin
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+
 import gettext
 import locale
 import os.path
diff --git a/picard/log.py b/picard/log.py
index d4faef298..1f4317f37 100644
--- a/picard/log.py
+++ b/picard/log.py
@@ -62,7 +62,7 @@ class Logger(object):
         for func in self._receivers:
             try:
                 thread.to_main(func, level, time, message)
-            except Exception as e:
+            except:
                 import traceback
                 traceback.print_exc()
 
diff --git a/picard/releasegroup.py b/picard/releasegroup.py
index 70d4bc031..274ecba28 100644
--- a/picard/releasegroup.py
+++ b/picard/releasegroup.py
@@ -21,8 +21,7 @@ import traceback
 from collections import defaultdict
 from functools import partial
 from itertools import combinations
-from PyQt4 import QtCore
-from picard import config, log
+from picard import log
 from picard.metadata import Metadata
 from picard.dataobj import DataObject
 from picard.mbxml import media_formats_from_node, label_info_from_node
diff --git a/picard/tagger.py b/picard/tagger.py
index b2d2208af..f5904fa51 100644
--- a/picard/tagger.py
+++ b/picard/tagger.py
@@ -26,7 +26,6 @@ import re
 import shutil
 import signal
 import sys
-from collections import deque
 from functools import partial
 from itertools import chain
 
@@ -61,7 +60,6 @@ from picard.track import Track, NonAlbumTrack
 from picard.releasegroup import ReleaseGroup
 from picard.collection import load_user_collections
 from picard.ui.mainwindow import MainWindow
-from picard.ui.itemviews import BaseTreeView
 from picard.plugin import PluginManager
 from picard.acoustidmanager import AcoustIDManager
 from picard.util import (
diff --git a/picard/ui/cdlookup.py b/picard/ui/cdlookup.py
index cc5bd4810..cd9355590 100644
--- a/picard/ui/cdlookup.py
+++ b/picard/ui/cdlookup.py
@@ -50,7 +50,8 @@ class CDLookupDialog(QtGui.QDialog):
                 item.setData(0, QtCore.Qt.UserRole, QtCore.QVariant(release.id))
             self.ui.release_list.setCurrentItem(self.ui.release_list.topLevelItem(0))
             self.ui.ok_button.setEnabled(True)
-        [self.ui.release_list.resizeColumnToContents(i) for i in range(self.ui.release_list.columnCount() - 1)]
+        for i in range(self.ui.release_list.columnCount() - 1):
+            self.ui.release_list.resizeColumnToContents(i)
         # Sort by descending date, then ascending country
         self.ui.release_list.sortByColumn(3, QtCore.Qt.AscendingOrder)
         self.ui.release_list.sortByColumn(2, QtCore.Qt.DescendingOrder)
diff --git a/picard/ui/filebrowser.py b/picard/ui/filebrowser.py
index c469aaa67..310a2f567 100644
--- a/picard/ui/filebrowser.py
+++ b/picard/ui/filebrowser.py
@@ -1,4 +1,4 @@
-# -*- coding: UTF-8 -*-
+# -*- coding: utf-8 -*-
 #
 # Picard, the next-generation MusicBrainz tagger
 # Copyright (C) 2006-2007 Lukáš Lalinský
diff --git a/picard/ui/infostatus.py b/picard/ui/infostatus.py
index 769a5b9db..bfb1c8dce 100644
--- a/picard/ui/infostatus.py
+++ b/picard/ui/infostatus.py
@@ -18,7 +18,6 @@
 
 from PyQt4 import QtCore, QtGui
 from PyQt4.QtGui import QIcon
-from picard import config
 from picard.util import icontheme
 from picard.ui.ui_infostatus import Ui_InfoStatus
 
diff --git a/picard/ui/itemviews.py b/picard/ui/itemviews.py
index 1a6d759d7..9b5d52ec8 100644
--- a/picard/ui/itemviews.py
+++ b/picard/ui/itemviews.py
@@ -308,7 +308,9 @@ class BaseTreeView(QtGui.QTreeWidget):
                             action.setChecked(True)
                         action.triggered.connect(partial(obj.switch_release_version, version["id"]))
 
-                _add_other_versions() if obj.release_group.loaded else \
+                if obj.release_group.loaded:
+                    _add_other_versions()
+                else:
                     obj.release_group.load_versions(_add_other_versions)
                 releases_menu.setEnabled(True)
             else:
diff --git a/picard/ui/mainwindow.py b/picard/ui/mainwindow.py
index 6d4ad1c2d..3e27eafc7 100644
--- a/picard/ui/mainwindow.py
+++ b/picard/ui/mainwindow.py
@@ -22,7 +22,6 @@ from PyQt4 import QtCore, QtGui
 import sys
 import os.path
 
-from functools import partial
 from picard import config, log
 from picard.file import File
 from picard.track import Track
diff --git a/picard/ui/metadatabox.py b/picard/ui/metadatabox.py
index bec999ff0..94b7d08ba 100644
--- a/picard/ui/metadatabox.py
+++ b/picard/ui/metadatabox.py
@@ -290,7 +290,9 @@ class MetadataBox(QtGui.QTableWidget):
         self.set_tag_values(tag, [""])
 
     def remove_selected_tags(self):
-        (self.remove_tag(tag) for tag in self.selected_tags() if self.tag_is_removable(tag))
+        for tag in self.selected_tags():
+            if self.tag_is_removable(tag):
+                self.remove_tag(tag)
 
     def tag_is_removable(self, tag):
         return self.tag_diff.status[tag] & TagStatus.NotRemovable == 0
diff --git a/picard/ui/options/dialog.py b/picard/ui/options/dialog.py
index 6a27b107b..9c49cfeb7 100644
--- a/picard/ui/options/dialog.py
+++ b/picard/ui/options/dialog.py
@@ -19,7 +19,6 @@
 
 from PyQt4 import QtCore, QtGui
 from picard import config
-from picard.plugin import ExtensionPoint
 from picard.util import webbrowser2
 from picard.ui.util import StandardButton
 from picard.ui.options import (
diff --git a/picard/ui/options/fingerprinting.py b/picard/ui/options/fingerprinting.py
index 52f0bc355..3a3e434ce 100644
--- a/picard/ui/options/fingerprinting.py
+++ b/picard/ui/options/fingerprinting.py
@@ -18,7 +18,7 @@
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 
 import os
-from PyQt4 import QtCore, QtGui
+from PyQt4 import QtGui
 from picard import config
 from picard.util import webbrowser2, find_executable
 from picard.const import FPCALC_NAMES
diff --git a/picard/ui/options/metadata.py b/picard/ui/options/metadata.py
index 6ee2eba21..410535844 100644
--- a/picard/ui/options/metadata.py
+++ b/picard/ui/options/metadata.py
@@ -17,7 +17,6 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 
-from PyQt4 import QtCore
 from picard import config
 from picard.ui.options import OptionsPage, register_options_page
 from picard.ui.ui_options_metadata import Ui_MetadataOptionsPage
diff --git a/picard/ui/passworddialog.py b/picard/ui/passworddialog.py
index 804e7e062..32335f519 100644
--- a/picard/ui/passworddialog.py
+++ b/picard/ui/passworddialog.py
@@ -17,7 +17,7 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 
-from PyQt4 import QtCore, QtGui
+from PyQt4 import QtGui
 from picard import config
 from picard.ui.ui_passworddialog import Ui_PasswordDialog
 from picard.util import rot13
diff --git a/picard/util/bytes2human.py b/picard/util/bytes2human.py
index bfc7ceca7..ea8fb4eb2 100644
--- a/picard/util/bytes2human.py
+++ b/picard/util/bytes2human.py
@@ -18,8 +18,6 @@
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 
 import locale
-import picard.i18n
-
 
 """
 Helper class to convert bytes to human-readable form
@@ -46,26 +44,26 @@ _BYTES_STRINGS_I18N = (
 )
 
 
-def decimal(number, prec=1):
+def decimal(number, scale=1):
     """
     Convert bytes to short human-readable string, decimal mode
 
     >>> [decimal(n) for n in [1000, 1024, 15500]]
     ['1 kB', '1 kB', '15.5 kB']
     """
-    return short_string(int(number), 1000)
+    return short_string(int(number), 1000, scale)
 
 
-def binary(number, prec=1):
+def binary(number, scale=1):
     """
     Convert bytes to short human-readable string, binary mode
     >>> [binary(n) for n in [1000, 1024, 15500]]
     ['1000 B', '1 KiB', '15.1 KiB']
     """
-    return short_string(int(number), 1024, prec)
+    return short_string(int(number), 1024, scale)
 
 
-def short_string(number, multiple, prec=1):
+def short_string(number, multiple, scale=1):
     """
     Returns short human-readable string for `number` bytes
     >>> [short_string(n, 1024, 2) for n in [1000, 1100, 15500]]
@@ -75,12 +73,12 @@ def short_string(number, multiple, prec=1):
     """
     num, unit = calc_unit(number, multiple)
     n = int(num)
-    nr = round(num, prec)
+    nr = round(num, scale)
     if n == nr or unit == 'B':
         fmt = '%d'
         num = n
     else:
-        fmt = '%%0.%df' % prec
+        fmt = '%%0.%df' % scale
         num = nr
     fmtnum = locale.format(fmt, num)
     return _("%s " + unit) % fmtnum
@@ -118,8 +116,3 @@ def calc_unit(number, multiple=1000):
             return (sign * n, suffix)
         else:
             n /= multiple
-
-
-if __name__ == "__main__":
-    import doctest
-    doctest.testmod()
diff --git a/picard/util/cdrom.py b/picard/util/cdrom.py
index 80651dafe..d506c6633 100644
--- a/picard/util/cdrom.py
+++ b/picard/util/cdrom.py
@@ -54,10 +54,12 @@ else:
     # setting uses a text field instead of a drop-down
     AUTO_DETECT_DRIVES = False
 
+
 def _split_values(s):
     """split a space separated list"""
     return QString(s).trimmed().split(QRegExp("\\s+"), QString.SkipEmptyParts)
 
+
 def get_cdrom_drives():
     """List available disc drives on the machine
     """
@@ -90,10 +92,11 @@ def get_cdrom_drives():
                     elif key == 'Can play audio':
                         drive_audio_caps = [v == '1'
                                             for v in _split_values(values)]
+                        break  # no need to continue past this line
                 line = cdinfo.readLine()
             # Show only drives that are capable of playing audio
-            for drive in drive_names:
-                if drive_audio_caps[drive_names.indexOf(drive)]:
+            for index, drive in enumerate(drive_names):
+                if drive_audio_caps[index]:
                     device = u'/dev/%s' % drive
                     symlink_target = QFile.symLinkTarget(device)
                     if symlink_target != '':
diff --git a/picard/util/thread.py b/picard/util/thread.py
index 8c9b36fbf..095f8bbab 100644
--- a/picard/util/thread.py
+++ b/picard/util/thread.py
@@ -19,7 +19,7 @@
 
 import sys
 import traceback
-from PyQt4.QtCore import QThreadPool, QRunnable, QCoreApplication, QEvent
+from PyQt4.QtCore import QRunnable, QCoreApplication, QEvent
 
 
 class ProxyToMainEvent(QEvent):
diff --git a/picard/webservice.py b/picard/webservice.py
index d9b17b8b8..721d34617 100644
--- a/picard/webservice.py
+++ b/picard/webservice.py
@@ -392,7 +392,7 @@ class XmlWebService(QtCore.QObject):
         query = []
         for name, value in kwargs.items():
             if name == 'limit':
-                filters.append((name, value))
+                filters.append((name, str(value)))
             else:
                 value = _escape_lucene_query(value).strip().lower()
                 if value:
diff --git a/test/test_bytes2human.py b/test/test_bytes2human.py
index 7a37737c2..9f8d53305 100644
--- a/test/test_bytes2human.py
+++ b/test/test_bytes2human.py
@@ -30,8 +30,11 @@ class Testbytes2human(unittest.TestCase):
 
         self.assertEqual(bytes2human.binary(45682), '44.6 KiB')
         self.assertEqual(bytes2human.binary(-45682), '-44.6 KiB')
+        self.assertEqual(bytes2human.binary(-45682, 2), '-44.61 KiB')
         self.assertEqual(bytes2human.decimal(45682), '45.7 kB')
+        self.assertEqual(bytes2human.decimal(45682, 2), '45.68 kB')
         self.assertEqual(bytes2human.decimal(9223372036854775807), '9223.4 PB')
+        self.assertEqual(bytes2human.decimal(9223372036854775807, 3), '9223.372 PB')
         self.assertEqual(bytes2human.decimal(123.6), '123 B')
         self.assertRaises(ValueError, bytes2human.decimal, 'xxx')
         self.assertRaises(ValueError, bytes2human.decimal, '123.6')