diff --git a/setup/mathjax.py b/setup/mathjax.py
index b65bba6935..5a49f07ce9 100644
--- a/setup/mathjax.py
+++ b/setup/mathjax.py
@@ -12,7 +12,6 @@ from io import BytesIO
 from zipfile import ZipFile, ZIP_STORED, ZipInfo
 from hashlib import sha1
 from tempfile import mkdtemp, SpooledTemporaryFile
-is_ci = os.environ.get('CI', '').lower() == 'true'
 
 
 from setup import Command, download_securely
diff --git a/src/calibre/ebooks/pdf/render/from_html.py b/src/calibre/ebooks/pdf/render/from_html.py
index 962917966c..b3e81f0a12 100644
--- a/src/calibre/ebooks/pdf/render/from_html.py
+++ b/src/calibre/ebooks/pdf/render/from_html.py
@@ -23,7 +23,7 @@ from calibre.ebooks.oeb.display.webview import load_html
 from calibre.ebooks.pdf.render.common import (inch, cm, mm, pica, cicero,
                                               didot, PAPER_SIZES, current_log)
 from calibre.ebooks.pdf.render.engine import PdfDevice
-from calibre.ptempfile import PersistentTemporaryFile, PersistentTemporaryDirectory
+from calibre.ptempfile import PersistentTemporaryFile
 from calibre.utils.resources import load_hyphenator_dicts
 
 
diff --git a/src/calibre/gui2/tag_browser/model.py b/src/calibre/gui2/tag_browser/model.py
index ce45ec0441..3077a28969 100644
--- a/src/calibre/gui2/tag_browser/model.py
+++ b/src/calibre/gui2/tag_browser/model.py
@@ -423,10 +423,8 @@ class TagsModel(QAbstractItemModel):  # {{{
 
             if self.category_custom_icons.get(key, None) is None:
                 self.category_custom_icons[key] = QIcon(I(
-                    category_icon_map['gst'] if is_gst else
-                        category_icon_map.get(key,
-                            (category_icon_map['user:'] if key.startswith('@') else
-                                category_icon_map['custom:']))))
+                    category_icon_map['gst'] if is_gst else category_icon_map.get(
+                        key, (category_icon_map['user:'] if key.startswith('@') else category_icon_map['custom:']))))
 
             if key.startswith('@'):
                 path_parts = [p for p in key.split('.')]
diff --git a/src/calibre/gui2/viewer/fake_net.py b/src/calibre/gui2/viewer/fake_net.py
index 12c7f28752..a8d5159a22 100644
--- a/src/calibre/gui2/viewer/fake_net.py
+++ b/src/calibre/gui2/viewer/fake_net.py
@@ -9,7 +9,6 @@ import os
 from PyQt5.Qt import QNetworkReply, QNetworkAccessManager, QUrl, QNetworkRequest, QTimer, pyqtSignal, QByteArray
 
 from calibre import guess_type as _guess_type, prints
-from calibre.ptempfile import PersistentTemporaryDirectory
 from calibre.constants import FAKE_HOST, FAKE_PROTOCOL, DEBUG
 from calibre.ebooks.oeb.base import OEB_DOCS
 from calibre.ebooks.oeb.display.webview import cleanup_html, load_as_html
diff --git a/src/calibre/srv/books.py b/src/calibre/srv/books.py
index 641cd80305..eb59b425d7 100644
--- a/src/calibre/srv/books.py
+++ b/src/calibre/srv/books.py
@@ -8,10 +8,8 @@ from hashlib import sha1
 from functools import partial
 from threading import RLock, Lock
 from cPickle import dumps
-from zipfile import ZipFile
 import errno, os, tempfile, shutil, time, json as jsonlib
 
-from lzma.xz import decompress
 from calibre.constants import cache_dir, iswindows
 from calibre.customize.ui import plugin_for_input_format
 from calibre.srv.metadata import book_as_json