diff --git a/setup/__init__.py b/setup/__init__.py
index ce2c0d6b0e..d92f2bcbeb 100644
--- a/setup/__init__.py
+++ b/setup/__init__.py
@@ -11,13 +11,13 @@ from contextlib import contextmanager
 
 is64bit = platform.architecture()[0] == '64bit'
 iswindows = re.search('win(32|64)', sys.platform)
-isosx = 'darwin' in sys.platform
+ismacos = 'darwin' in sys.platform
 isfreebsd = 'freebsd' in sys.platform
 isnetbsd = 'netbsd' in sys.platform
 isdragonflybsd = 'dragonfly' in sys.platform
 isbsd = isnetbsd or isfreebsd or isdragonflybsd
 ishaiku = 'haiku1' in sys.platform
-islinux = not isosx and not iswindows and not isbsd and not ishaiku
+islinux = not ismacos and not iswindows and not isbsd and not ishaiku
 sys.setup_dir = os.path.dirname(os.path.abspath(__file__))
 SRC = os.path.abspath(os.path.join(os.path.dirname(sys.setup_dir), 'src'))
 sys.path.insert(0, SRC)
@@ -160,7 +160,7 @@ class Command(object):
         self.real_user = os.environ.get('SUDO_USER', None)
 
     def drop_privileges(self):
-        if not islinux or isosx or isfreebsd:
+        if not islinux or ismacos or isfreebsd:
             return
         if self.real_user is not None:
             self.info('Dropping privileges to those of', self.real_user+':',
@@ -171,7 +171,7 @@ class Command(object):
             os.seteuid(int(self.real_uid))
 
     def regain_privileges(self):
-        if not islinux or isosx or isfreebsd:
+        if not islinux or ismacos or isfreebsd:
             return
         if os.geteuid() != 0 and self.orig_euid == 0:
             self.info('Trying to get root privileges')
diff --git a/setup/build.py b/setup/build.py
index ef93146a56..4268d19bce 100644
--- a/setup/build.py
+++ b/setup/build.py
@@ -8,8 +8,8 @@ __docformat__ = 'restructuredtext en'
 import textwrap, os, shlex, subprocess, glob, shutil, re, sys, json
 from collections import namedtuple
 
-from setup import Command, islinux, isbsd, isfreebsd, isosx, ishaiku, SRC, iswindows, __version__
-isunix = islinux or isosx or isbsd or ishaiku
+from setup import Command, islinux, isbsd, isfreebsd, ismacos, ishaiku, SRC, iswindows, __version__
+isunix = islinux or ismacos or isbsd or ishaiku
 
 py_lib = os.path.join(sys.prefix, 'libs', 'python%d%d.lib' % sys.version_info[:2])
 CompileCommand = namedtuple('CompileCommand', 'cmd src dest')
@@ -118,7 +118,7 @@ def parse_extension(ext):
         ans = ext.pop(k, default)
         if iswindows:
             ans = ext.pop('windows_' + k, ans)
-        elif isosx:
+        elif ismacos:
             ans = ext.pop('osx_' + k, ans)
         elif isbsd:
             ans = ext.pop('bsd_' + k, ans)
@@ -192,7 +192,7 @@ def init_env():
         ldflags.append('-lpython{}{}'.format(
             sysconfig.get_config_var('VERSION'), getattr(sys, 'abiflags', '')))
 
-    if isosx:
+    if ismacos:
         cflags.append('-D_OSX')
         ldflags.extend('-bundle -undefined dynamic_lookup'.split())
         cflags.extend(['-fno-common', '-dynamic'])
@@ -420,7 +420,7 @@ class Build(Command):
             'calibre/headless/headless_backingstore.cpp',
             'calibre/headless/headless_integration.cpp',
         ])
-        if isosx:
+        if ismacos:
             sources.extend(a(['calibre/headless/coretext_fontdatabase.mm']))
         else:
             headers.extend(a(['calibre/headless/fontconfig_database.h']))
@@ -462,7 +462,7 @@ class Build(Command):
             self.check_call([self.env.make] + ['-j%d'%(cpu_count or 1)])
         finally:
             os.chdir(cwd)
-        if isosx:
+        if ismacos:
             os.rename(self.j(self.d(target), 'libheadless.dylib'), self.j(self.d(target), 'headless.so'))
 
     def get_sip_commands(self, ext):
@@ -524,7 +524,7 @@ class Build(Command):
         )
         for incdir in ext.inc_dirs:
             pro += '\nINCLUDEPATH += ' + incdir
-        if not iswindows and not isosx:
+        if not iswindows and not ismacos:
             # Ensure that only the init symbol is exported
             pro += '\nQMAKE_LFLAGS += -Wl,--version-script=%s.exp' % sip['target']
             with open(os.path.join(src_dir, sip['target'] + '.exp'), 'wb') as f:
@@ -539,7 +539,7 @@ class Build(Command):
         qmc = []
         if iswindows:
             qmc += ['-spec', qmakespec]
-        fext = 'dll' if iswindows else 'dylib' if isosx else 'so'
+        fext = 'dll' if iswindows else 'dylib' if ismacos else 'so'
         name = '%s%s.%s' % ('release/' if iswindows else 'lib', sip['target'], fext)
         try:
             os.chdir(src_dir)
diff --git a/setup/build_environment.py b/setup/build_environment.py
index b5bfee12a1..160fbbb70c 100644
--- a/setup/build_environment.py
+++ b/setup/build_environment.py
@@ -9,7 +9,7 @@ __docformat__ = 'restructuredtext en'
 import os, subprocess, re, sys, sysconfig
 from distutils.spawn import find_executable
 
-from setup import isfreebsd, isosx, iswindows, is64bit, islinux, ishaiku
+from setup import isfreebsd, ismacos, iswindows, is64bit, islinux, ishaiku
 is64bit
 
 NMAKE = RC = msvc = MT = win_inc = win_lib = None
@@ -162,7 +162,7 @@ if iswindows:
     zlib_lib_dirs = [sw_lib_dir]
     podofo_inc = os.path.join(sw_inc_dir, 'podofo')
     podofo_lib = sw_lib_dir
-elif isosx:
+elif ismacos:
     sw = os.environ.get('SW', os.path.expanduser('~/sw'))
     sw_inc_dir  = os.path.join(sw, 'include')
     sw_lib_dir  = os.path.join(sw, 'lib')
diff --git a/setup/test.py b/setup/test.py
index 5cc4d5a3b5..16775d0b9f 100644
--- a/setup/test.py
+++ b/setup/test.py
@@ -6,7 +6,7 @@
 import os
 import unittest
 
-from setup import Command, islinux, isosx, iswindows, SRC
+from setup import Command, islinux, ismacos, iswindows, SRC
 
 TEST_MODULES = frozenset('srv db polish opf css docx cfi matcher icu smartypants build misc dbcli ebooks'.split())
 
@@ -42,7 +42,7 @@ class TestImports(unittest.TestCase):
         if not iswindows:
             exclude_modules |= {'calibre.utils.iphlpapi', 'calibre.utils.open_with.windows', 'calibre.devices.winusb'}
             exclude_packages |= {'calibre.utils.winreg'}
-        if not isosx:
+        if not ismacos:
             exclude_modules.add('calibre.utils.open_with.osx')
         if not islinux:
             exclude_modules |= {
diff --git a/src/calibre/__init__.py b/src/calibre/__init__.py
index 25a13ffac1..c8fa6f3fb6 100644
--- a/src/calibre/__init__.py
+++ b/src/calibre/__init__.py
@@ -16,7 +16,7 @@ try:
 except EnvironmentError:
     os.chdir(os.path.expanduser('~'))
 
-from calibre.constants import (iswindows, isosx, islinux, isfrozen,
+from calibre.constants import (iswindows, ismacos, islinux, isfrozen,
         isbsd, preferred_encoding, __appname__, __version__, __author__,
         win32event, win32api, winerror, fcntl,
         filesystem_encoding, plugins, config_dir)
@@ -94,7 +94,7 @@ def unicode_path(path, abs=False):
 
 
 def osx_version():
-    if isosx:
+    if ismacos:
         import platform
         src = platform.mac_ver()[0]
         m = re.match(r'(\d+)\.(\d+)\.(\d+)', src)
@@ -169,7 +169,7 @@ def setup_cli_handlers(logger, level):
 def load_library(name, cdll):
     if iswindows:
         return cdll.LoadLibrary(name)
-    if isosx:
+    if ismacos:
         name += '.dylib'
         if hasattr(sys, 'frameworks_dir'):
             return cdll.LoadLibrary(os.path.join(getattr(sys, 'frameworks_dir'), name))
diff --git a/src/calibre/constants.py b/src/calibre/constants.py
index 21b78334d2..c5886370cd 100644
--- a/src/calibre/constants.py
+++ b/src/calibre/constants.py
@@ -17,16 +17,16 @@ Various run time constants.
 
 _plat = sys.platform.lower()
 iswindows = 'win32' in _plat or 'win64' in _plat
-isosx     = 'darwin' in _plat
-isnewosx  = isosx and getattr(sys, 'new_app_bundle', False)
+ismacos = isosx = 'darwin' in _plat
+isnewosx  = ismacos and getattr(sys, 'new_app_bundle', False)
 isfreebsd = 'freebsd' in _plat
 isnetbsd = 'netbsd' in _plat
 isdragonflybsd = 'dragonfly' in _plat
 isbsd = isfreebsd or isnetbsd or isdragonflybsd
 ishaiku = 'haiku1' in _plat
-islinux   = not(iswindows or isosx or isbsd or ishaiku)
+islinux   = not(iswindows or ismacos or isbsd or ishaiku)
 isfrozen  = hasattr(sys, 'frozen')
-isunix = isosx or islinux or ishaiku
+isunix = ismacos or islinux or ishaiku
 isportable = hasenv('CALIBRE_PORTABLE_BUILD')
 ispy3 = sys.version_info.major > 2
 isxp = isoldvista = False
@@ -143,7 +143,7 @@ def _get_cache_dir():
             candidate = os.path.join(w.special_folder_path(w.CSIDL_LOCAL_APPDATA), '%s-cache'%__appname__)
         except ValueError:
             return confcache
-    elif isosx:
+    elif ismacos:
         candidate = os.path.join(os.path.expanduser('~/Library/Caches'), __appname__)
     else:
         candidate = getenv('XDG_CACHE_HOME', '~/.cache')
@@ -203,10 +203,10 @@ class Plugins(collections.Mapping):
             ]
         if iswindows:
             plugins.extend(['winutil', 'wpd', 'winfonts'])
-        if isosx:
+        if ismacos:
             plugins.append('usbobserver')
             plugins.append('cocoa')
-        if isfreebsd or ishaiku or islinux or isosx:
+        if isfreebsd or ishaiku or islinux or ismacos:
             plugins.append('libusb')
             plugins.append('libmtp')
         self.plugins = frozenset(plugins)
@@ -269,7 +269,7 @@ elif iswindows:
     if not config_dir or not os.access(config_dir, os.W_OK|os.X_OK):
         config_dir = os.path.expanduser('~')
     config_dir = os.path.join(config_dir, 'calibre')
-elif isosx:
+elif ismacos:
     config_dir = os.path.expanduser('~/Library/Preferences/calibre')
 else:
     bdir = os.path.abspath(os.path.expanduser(getenv('XDG_CONFIG_HOME', '~/.config')))
diff --git a/src/calibre/customize/__init__.py b/src/calibre/customize/__init__.py
index 8de6759c98..2c4bc1d1ce 100644
--- a/src/calibre/customize/__init__.py
+++ b/src/calibre/customize/__init__.py
@@ -4,14 +4,14 @@ __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
 
 import os, sys, zipfile, importlib
 
-from calibre.constants import numeric_version, iswindows, isosx
+from calibre.constants import numeric_version, iswindows, ismacos
 from calibre.ptempfile import PersistentTemporaryFile
 from polyglot.builtins import unicode_type
 
 platform = 'linux'
 if iswindows:
     platform = 'windows'
-elif isosx:
+elif ismacos:
     platform = 'osx'
 
 
diff --git a/src/calibre/db/adding.py b/src/calibre/db/adding.py
index dbe723bb72..8059afcf3a 100644
--- a/src/calibre/db/adding.py
+++ b/src/calibre/db/adding.py
@@ -12,7 +12,7 @@ from contextlib import contextmanager
 from functools import partial
 
 from calibre import prints
-from calibre.constants import iswindows, isosx, filesystem_encoding
+from calibre.constants import iswindows, ismacos, filesystem_encoding
 from calibre.ebooks import BOOK_EXTENSIONS
 
 
@@ -72,7 +72,7 @@ def metadata_extensions():
     return _metadata_extensions
 
 
-if iswindows or isosx:
+if iswindows or ismacos:
     unicode_listdir = os.listdir
 else:
     def unicode_listdir(root):
diff --git a/src/calibre/db/delete_service.py b/src/calibre/db/delete_service.py
index 8be9cd4ffd..23aeaa01c9 100644
--- a/src/calibre/db/delete_service.py
+++ b/src/calibre/db/delete_service.py
@@ -8,7 +8,7 @@ __copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 import os, tempfile, shutil, errno, time, atexit
 from threading import Thread
 
-from calibre.constants import isosx, plugins
+from calibre.constants import ismacos, plugins
 from calibre.ptempfile import remove_dir
 from calibre.utils.filenames import remove_dir_if_empty
 from calibre.utils.recycle_bin import delete_tree, delete_file
@@ -34,7 +34,7 @@ class DeleteService(Thread):
     def __init__(self):
         Thread.__init__(self)
         self.requests = Queue()
-        if isosx:
+        if ismacos:
             plugins['cocoa'][0].enable_cocoa_multithreading()
 
     def shutdown(self, timeout=20):
diff --git a/src/calibre/debug.py b/src/calibre/debug.py
index 04106baa7e..dcad481c4f 100644
--- a/src/calibre/debug.py
+++ b/src/calibre/debug.py
@@ -181,7 +181,7 @@ def print_basic_debug_info(out=None):
         out = sys.stdout
     out = functools.partial(prints, file=out)
     import platform
-    from calibre.constants import (__appname__, get_version, isportable, isosx,
+    from calibre.constants import (__appname__, get_version, isportable, ismacos,
                                    isfrozen, is64bit)
     from calibre.utils.localization import set_translators
     out(__appname__, get_version(), 'Portable' if isportable else '',
@@ -200,7 +200,7 @@ def print_basic_debug_info(out=None):
     try:
         if iswindows:
             out('Windows:', platform.win32_ver())
-        elif isosx:
+        elif ismacos:
             out('OSX:', platform.mac_ver())
         else:
             out('Linux:', platform.linux_distribution())
diff --git a/src/calibre/devices/__init__.py b/src/calibre/devices/__init__.py
index a561e40efe..cf25074d43 100644
--- a/src/calibre/devices/__init__.py
+++ b/src/calibre/devices/__init__.py
@@ -72,7 +72,7 @@ def debug(ioreg_to_tmp=False, buf=None, plugins=None,
     from calibre.customize.ui import device_plugins, disabled_device_plugins
     from calibre.debug import print_basic_debug_info
     from calibre.devices.scanner import DeviceScanner
-    from calibre.constants import iswindows, isosx
+    from calibre.constants import iswindows, ismacos
     from calibre import prints
     from polyglot.io import PolyglotStringIO
     oldo, olde = sys.stdout, sys.stderr
@@ -108,7 +108,7 @@ def debug(ioreg_to_tmp=False, buf=None, plugins=None,
         out(pprint.pformat(devices))
 
         ioreg = None
-        if isosx:
+        if ismacos:
             from calibre.devices.usbms.device import Device
             mount = '\n'.join(repr(x) for x in Device.osx_run_mount().splitlines())
             drives = pprint.pformat(Device.osx_get_usb_drives())
diff --git a/src/calibre/devices/mtp/unix/driver.py b/src/calibre/devices/mtp/unix/driver.py
index ad882f6fa5..9ab7502041 100644
--- a/src/calibre/devices/mtp/unix/driver.py
+++ b/src/calibre/devices/mtp/unix/driver.py
@@ -11,7 +11,7 @@ from collections import namedtuple
 from functools import partial
 
 from calibre import prints, as_unicode, force_unicode
-from calibre.constants import plugins, islinux, isosx
+from calibre.constants import plugins, islinux, ismacos
 from calibre.ptempfile import SpooledTemporaryFile
 from calibre.devices.errors import OpenFailed, DeviceError, BlacklistedDevice, OpenActionNeeded
 from calibre.devices.mtp.base import MTPDeviceBase, synchronous, debug
@@ -51,7 +51,7 @@ class MTP_DEVICE(MTPDeviceBase):
         if islinux:
             from calibre.devices.mtp.unix.sysfs import MTPDetect
             self._is_device_mtp = MTPDetect()
-        if isosx and 'osx' in self.supported_platforms:
+        if ismacos and 'osx' in self.supported_platforms:
             self.usbobserver, err = plugins['usbobserver']
             if err:
                 raise RuntimeError(err)
diff --git a/src/calibre/devices/scanner.py b/src/calibre/devices/scanner.py
index 924091605f..c7aeeadadf 100644
--- a/src/calibre/devices/scanner.py
+++ b/src/calibre/devices/scanner.py
@@ -11,7 +11,7 @@ from collections import namedtuple
 from threading import Lock
 
 from calibre import prints, as_unicode
-from calibre.constants import (iswindows, isosx, plugins, islinux, isfreebsd,
+from calibre.constants import (iswindows, ismacos, plugins, islinux, isfreebsd,
         isnetbsd)
 from polyglot.builtins import range
 
@@ -172,7 +172,7 @@ if islinux:
     linux_scanner = LinuxScanner()
 
 libusb_scanner = LibUSBScanner()
-if False and isosx:
+if False and ismacos:
     # Apparently libusb causes mem leaks on some Macs and hangs on others and
     # works on a few. OS X users will just have to live without MTP support.
     # See https://bugs.launchpad.net/calibre/+bug/1044706
@@ -196,7 +196,7 @@ class DeviceScanner(object):
     def __init__(self, *args):
         if iswindows:
             from calibre.devices.winusb import scan_usb_devices as win_scanner
-        self.scanner = (win_scanner if iswindows else osx_scanner if isosx else
+        self.scanner = (win_scanner if iswindows else osx_scanner if ismacos else
                 freebsd_scanner if isfreebsd else netbsd_scanner if isnetbsd
                 else linux_scanner if islinux else libusb_scanner)
         if self.scanner is None:
diff --git a/src/calibre/devices/usbms/device.py b/src/calibre/devices/usbms/device.py
index 67f45964ba..c2e5dad67f 100644
--- a/src/calibre/devices/usbms/device.py
+++ b/src/calibre/devices/usbms/device.py
@@ -21,11 +21,11 @@ from calibre.constants import DEBUG
 from calibre.devices.interface import DevicePlugin
 from calibre.devices.errors import DeviceError
 from calibre.devices.usbms.deviceconfig import DeviceConfig
-from calibre.constants import iswindows, islinux, isosx, isfreebsd, plugins
+from calibre.constants import iswindows, islinux, ismacos, isfreebsd, plugins
 from calibre.utils.filenames import ascii_filename as sanitize
 from polyglot.builtins import iteritems, string_or_bytes, map
 
-if isosx:
+if ismacos:
     usbobserver, usbobserver_err = plugins['usbobserver']
     osx_sanitize_name_pat = re.compile(r'[.-]')
 
@@ -819,7 +819,7 @@ class Device(DeviceConfig, DevicePlugin):
                     self.open_freebsd()
             if iswindows:
                 self.open_windows()
-            if isosx:
+            if ismacos:
                 try:
                     self.open_osx()
                 except DeviceError:
@@ -891,7 +891,7 @@ class Device(DeviceConfig, DevicePlugin):
                 self.eject_windows()
             except:
                 pass
-        if isosx:
+        if ismacos:
             try:
                 self.eject_osx()
             except:
diff --git a/src/calibre/ebooks/mobi/writer8/exth.py b/src/calibre/ebooks/mobi/writer8/exth.py
index 9f737456a0..cc8a9ca58c 100644
--- a/src/calibre/ebooks/mobi/writer8/exth.py
+++ b/src/calibre/ebooks/mobi/writer8/exth.py
@@ -10,7 +10,7 @@ import re
 from struct import pack
 from io import BytesIO
 
-from calibre.constants import iswindows, isosx
+from calibre.constants import iswindows, ismacos
 from calibre.ebooks.mobi.utils import (utf8_text, to_base)
 from calibre.utils.localization import lang_as_iso639_1
 from calibre.ebooks.metadata import authors_to_sort_string
@@ -154,7 +154,7 @@ def build_exth(metadata, prefer_author_sort=False, is_periodical=False,
         nrecs += 1
 
     if be_kindlegen2:
-        mv = 200 if iswindows else 202 if isosx else 201
+        mv = 200 if iswindows else 202 if ismacos else 201
         vals = {204:mv, 205:2, 206:9, 207:0}
     elif is_periodical:
         # Pretend to be amazon's super secret periodical generator
diff --git a/src/calibre/ebooks/pdf/pdftohtml.py b/src/calibre/ebooks/pdf/pdftohtml.py
index 9b4f41fba1..02c610536b 100644
--- a/src/calibre/ebooks/pdf/pdftohtml.py
+++ b/src/calibre/ebooks/pdf/pdftohtml.py
@@ -10,7 +10,7 @@ import subprocess
 import sys
 
 from calibre import CurrentDir, prints, xml_replace_entities
-from calibre.constants import isbsd, islinux, isosx, iswindows
+from calibre.constants import isbsd, islinux, ismacos, iswindows
 from calibre.ebooks import ConversionError, DRMError
 from calibre.ebooks.chardet import xml_to_unicode
 from calibre.ptempfile import PersistentTemporaryFile
@@ -26,7 +26,7 @@ def popen(cmd, **kw):
     return subprocess.Popen(cmd, **kw)
 
 
-if isosx and hasattr(sys, 'frameworks_dir'):
+if ismacos and hasattr(sys, 'frameworks_dir'):
     base = os.path.join(os.path.dirname(sys.frameworks_dir), 'utils.app', 'Contents', 'MacOS')
     PDFTOHTML = os.path.join(base, PDFTOHTML)
 if iswindows and hasattr(sys, 'frozen'):
diff --git a/src/calibre/gui2/__init__.py b/src/calibre/gui2/__init__.py
index 8b4633b841..9f7252694e 100644
--- a/src/calibre/gui2/__init__.py
+++ b/src/calibre/gui2/__init__.py
@@ -25,7 +25,7 @@ from PyQt5.QtWidgets import QStyle  # Gives a nicer error message than import fr
 from calibre import as_unicode, prints
 from calibre.constants import (
     DEBUG, __appname__ as APP_UID, __version__, config_dir, filesystem_encoding,
-    is_running_from_develop, isbsd, isfrozen, islinux, isosx, iswindows, isxp,
+    is_running_from_develop, isbsd, isfrozen, islinux, ismacos, iswindows, isxp,
     plugins, plugins_loc
 )
 from calibre.ebooks.metadata import MetaInformation
@@ -69,7 +69,7 @@ native_menubar_defaults = {
 
 def create_defs():
     defs = gprefs.defaults
-    if isosx:
+    if ismacos:
         defs['action-layout-menubar'] = native_menubar_defaults['action-layout-menubar']
         defs['action-layout-menubar-device'] = native_menubar_defaults['action-layout-menubar-device']
         defs['action-layout-toolbar'] = (
@@ -147,7 +147,7 @@ def create_defs():
     defs['blocked_auto_formats'] = []
     defs['auto_add_auto_convert'] = True
     defs['auto_add_everything'] = False
-    defs['ui_style'] = 'calibre' if iswindows or isosx else 'system'
+    defs['ui_style'] = 'calibre' if iswindows or ismacos else 'system'
     defs['tag_browser_old_look'] = False
     defs['tag_browser_hide_empty_categories'] = False
     defs['tag_browser_always_autocollapse'] = False
@@ -663,7 +663,7 @@ if iswindows and 'CALIBRE_NO_NATIVE_FILEDIALOGS' not in os.environ:
     from calibre.gui2.win_file_dialogs import is_ok as has_windows_file_dialog_helper
     has_windows_file_dialog_helper = has_windows_file_dialog_helper()
 has_linux_file_dialog_helper = False
-if not iswindows and not isosx and 'CALIBRE_NO_NATIVE_FILEDIALOGS' not in os.environ and getattr(sys, 'frozen', False):
+if not iswindows and not ismacos and 'CALIBRE_NO_NATIVE_FILEDIALOGS' not in os.environ and getattr(sys, 'frozen', False):
     has_linux_file_dialog_helper = check_for_linux_native_dialogs()
 
 if has_windows_file_dialog_helper:
@@ -883,7 +883,7 @@ class Application(QApplication):
         self.pi, pi_err = plugins['progress_indicator']
         if pi_err:
             raise RuntimeError('Failed to load the progress_indicator C extension, with error: {}'.format(pi_err))
-        if not isosx and not headless:
+        if not ismacos and not headless:
             # On OS X high dpi scaling is turned on automatically by the OS, so we dont need to set it explicitly
             setup_hidpi()
         QApplication.setOrganizationName('calibre-ebook.com')
@@ -897,7 +897,7 @@ class Application(QApplication):
         sh = self.styleHints()
         if hasattr(sh, 'setShowShortcutsInContextMenus'):
             sh.setShowShortcutsInContextMenus(True)
-        if isosx:
+        if ismacos:
             plugins['cocoa'][0].disable_cocoa_ui_elements()
         self.setAttribute(Qt.AA_UseHighDpiPixmaps)
         self.setAttribute(Qt.AA_SynthesizeTouchForUnhandledMouseEvents, False)
@@ -929,7 +929,7 @@ class Application(QApplication):
             if s is not None:
                 font.setStretch(s)
             QApplication.setFont(font)
-        if not isosx and not iswindows:
+        if not ismacos and not iswindows:
             # Qt 5.10.1 on Linux resets the global font on first event loop tick.
             # So workaround it by setting the font once again in a timer.
             font_from_prefs = self.font()
@@ -947,7 +947,7 @@ class Application(QApplication):
         self._file_open_paths = []
         self._file_open_lock = RLock()
 
-        if not isosx:
+        if not ismacos:
             # OS X uses a native color dialog that does not support custom
             # colors
             self.color_prefs = color_prefs
@@ -975,7 +975,7 @@ class Application(QApplication):
             # Qt 5 bug: https://bugreports.qt-project.org/browse/QTBUG-41125
             self.aboutToQuit.connect(self.flush_clipboard)
 
-        if isosx:
+        if ismacos:
             cocoa, err = plugins['cocoa']
             if err:
                 raise RuntimeError('Failed to load cocoa plugin with error: {}'.format(err))
@@ -1038,7 +1038,7 @@ class Application(QApplication):
         self.set_palette(dark_palette())
 
     def setup_styles(self, force_calibre_style):
-        if iswindows or isosx:
+        if iswindows or ismacos:
             using_calibre_style = gprefs['ui_style'] != 'system'
         else:
             using_calibre_style = os.environ.get('CALIBRE_USE_SYSTEM_THEME', '0') == '0'
@@ -1047,7 +1047,7 @@ class Application(QApplication):
         if using_calibre_style:
             use_dark_palette = False
             if 'CALIBRE_USE_DARK_PALETTE' in os.environ:
-                if not isosx:
+                if not ismacos:
                     use_dark_palette = os.environ['CALIBRE_USE_DARK_PALETTE'] != '0'
             else:
                 if iswindows:
@@ -1087,7 +1087,7 @@ class Application(QApplication):
             return
         self.is_dark_theme = is_dark_theme()
         self.setProperty('is_dark_theme', self.is_dark_theme)
-        if isosx and self.is_dark_theme and self.using_calibre_style:
+        if ismacos and self.is_dark_theme and self.using_calibre_style:
             QTimer.singleShot(0, self.fix_combobox_text_color)
         if self.using_calibre_style:
             ss = 'QTabBar::tab:selected { font-style: italic }\n\n'
@@ -1132,7 +1132,7 @@ class Application(QApplication):
             v = pcache[v]
             icon_map[getattr(QStyle, 'SP_'+k)] = v
         transient_scroller = 0
-        if isosx:
+        if ismacos:
             transient_scroller = plugins['cocoa'][0].transient_scroller()
         icon_map[QStyle.SP_CustomBase + 1] = I('close-for-light-theme.png')
         icon_map[QStyle.SP_CustomBase + 2] = I('close-for-dark-theme.png')
@@ -1215,7 +1215,7 @@ def sanitize_env_vars():
         env_vars = {'LD_LIBRARY_PATH':'/lib'}
     elif iswindows:
         env_vars = {}
-    elif isosx:
+    elif ismacos:
         env_vars = {k:None for k in (
                     'FONTCONFIG_FILE FONTCONFIG_PATH SSL_CERT_FILE').split()}
     else:
@@ -1300,10 +1300,10 @@ def ensure_app(headless=True):
     with _ea_lock:
         if _store_app is None and QApplication.instance() is None:
             args = sys.argv[:1]
-            has_headless = isosx or islinux or isbsd
+            has_headless = ismacos or islinux or isbsd
             if headless and has_headless:
                 args += ['-platformpluginpath', plugins_loc, '-platform', 'headless']
-                if isosx:
+                if ismacos:
                     os.environ['QT_MAC_DISABLE_FOREGROUND_APPLICATION_TRANSFORM'] = '1'
             if headless and iswindows:
                 QApplication.setAttribute(Qt.AA_UseSoftwareOpenGL, True)
diff --git a/src/calibre/gui2/actions/__init__.py b/src/calibre/gui2/actions/__init__.py
index 9f30b5f997..eed9a9f566 100644
--- a/src/calibre/gui2/actions/__init__.py
+++ b/src/calibre/gui2/actions/__init__.py
@@ -13,7 +13,7 @@ from PyQt5.Qt import (QToolButton, QAction, QIcon, QObject, QMenu,
         QKeySequence)
 
 from calibre import prints
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.gui2 import Dispatcher
 from calibre.gui2.keyboard import NameConflict
 from polyglot.builtins import unicode_type, string_or_bytes
@@ -201,7 +201,7 @@ class InterfaceAction(QObject):
                         QKeySequence.PortableText) for key in keys])
                 else:
                     self.shortcut_action_for_context_menu = shortcut_action
-                    if isosx:
+                    if ismacos:
                         # In Qt 5 keyboard shortcuts dont work unless the
                         # action is explicitly added to the main window
                         self.gui.addAction(shortcut_action)
diff --git a/src/calibre/gui2/actions/copy_to_library.py b/src/calibre/gui2/actions/copy_to_library.py
index e8f6f9c227..a78582bd72 100644
--- a/src/calibre/gui2/actions/copy_to_library.py
+++ b/src/calibre/gui2/actions/copy_to_library.py
@@ -18,7 +18,7 @@ from PyQt5.Qt import (
     QScrollArea, QVBoxLayout, Qt, QListWidgetItem, QListWidget, QSize)
 
 from calibre import as_unicode
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.gui2.actions import InterfaceAction
 from calibre.gui2 import (error_dialog, Dispatcher, warning_dialog, gprefs,
         info_dialog, choose_dir)
@@ -374,7 +374,7 @@ class CopyToLibraryAction(InterfaceAction):
             self.menu.addAction(_('Choose library...'), self.choose_library)
 
         self.qaction.setVisible(bool(locations))
-        if isosx:
+        if ismacos:
             # The cloned action has to have its menu updated
             self.qaction.changed.emit()
 
diff --git a/src/calibre/gui2/actions/delete.py b/src/calibre/gui2/actions/delete.py
index 6577812fc0..a1eb64d8b1 100644
--- a/src/calibre/gui2/actions/delete.py
+++ b/src/calibre/gui2/actions/delete.py
@@ -12,7 +12,7 @@ from collections import Counter
 
 from PyQt5.Qt import QObject, QTimer, QModelIndex
 
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.gui2 import error_dialog, question_dialog
 from calibre.gui2.dialogs.delete_matching_from_device import DeleteMatchingFromDeviceDialog
 from calibre.gui2.dialogs.confirm_delete import confirm
@@ -87,7 +87,7 @@ class MultiDeleter(QObject):  # {{{
 class DeleteAction(InterfaceAction):
 
     name = 'Remove Books'
-    action_spec = (_('Remove books'), 'remove_books.png', _('Delete books'), 'Backspace' if isosx else 'Del')
+    action_spec = (_('Remove books'), 'remove_books.png', _('Delete books'), 'Backspace' if ismacos else 'Del')
     action_type = 'current'
     action_add_menu = True
     action_menu_clone_qaction = _('Remove selected books')
diff --git a/src/calibre/gui2/actions/preferences.py b/src/calibre/gui2/actions/preferences.py
index b9e120b4c1..8deefa5e27 100644
--- a/src/calibre/gui2/actions/preferences.py
+++ b/src/calibre/gui2/actions/preferences.py
@@ -13,7 +13,7 @@ from PyQt5.Qt import QIcon, Qt
 from calibre.gui2.actions import InterfaceAction
 from calibre.gui2.preferences.main import Preferences
 from calibre.gui2 import error_dialog, show_restart_warning
-from calibre.constants import DEBUG, isosx
+from calibre.constants import DEBUG, ismacos
 
 
 class PreferencesAction(InterfaceAction):
@@ -26,7 +26,7 @@ class PreferencesAction(InterfaceAction):
     def genesis(self):
         pm = self.qaction.menu()
         cm = partial(self.create_menu_action, pm)
-        if isosx:
+        if ismacos:
             pm.addAction(QIcon(I('config.png')), _('Preferences'), self.do_config)
         cm('welcome wizard', _('Run Welcome wizard'),
                 icon='wizard.png', triggered=self.gui.run_wizard)
diff --git a/src/calibre/gui2/actions/unpack_book.py b/src/calibre/gui2/actions/unpack_book.py
index 278cb968e0..08b14f1cdc 100644
--- a/src/calibre/gui2/actions/unpack_book.py
+++ b/src/calibre/gui2/actions/unpack_book.py
@@ -12,7 +12,7 @@ from PyQt5.Qt import (QDialog, QVBoxLayout, QHBoxLayout, QRadioButton, QFrame,
         QPushButton, QLabel, QGroupBox, QGridLayout, QIcon, QSize, QTimer)
 
 from calibre import as_unicode
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.gui2 import error_dialog, question_dialog, open_local_file, gprefs
 from calibre.gui2.actions import InterfaceAction
 from calibre.ptempfile import (PersistentTemporaryDirectory,
@@ -255,7 +255,7 @@ class UnpackBook(QDialog):
         self.reject()
 
     def cleanup(self):
-        if isosx and self._exploded:
+        if ismacos and self._exploded:
             try:
                 import appscript
                 self.finder = appscript.app('Finder')
diff --git a/src/calibre/gui2/actions/view.py b/src/calibre/gui2/actions/view.py
index 5eac859b3b..9f71d1bb78 100644
--- a/src/calibre/gui2/actions/view.py
+++ b/src/calibre/gui2/actions/view.py
@@ -11,7 +11,7 @@ from functools import partial
 
 from PyQt5.Qt import Qt, QAction, pyqtSignal
 
-from calibre.constants import isosx, iswindows, plugins
+from calibre.constants import ismacos, iswindows, plugins
 from calibre.gui2 import (
     error_dialog, Dispatcher, question_dialog, config, open_local_file,
     info_dialog, elided_text)
@@ -135,7 +135,7 @@ class ViewAction(InterfaceAction):
         try:
             if internal:
                 args = [viewer]
-                if isosx and 'ebook' in viewer:
+                if ismacos and 'ebook' in viewer:
                     args.append('--raise-window')
 
                 if name is not None:
@@ -247,7 +247,7 @@ class ViewAction(InterfaceAction):
         for i, row in enumerate(rows):
             path = self.gui.library_view.model().db.abspath(row.row())
             open_local_file(path)
-            if isosx and i < len(rows) - 1:
+            if ismacos and i < len(rows) - 1:
                 time.sleep(0.1)  # Finder cannot handle multiple folder opens
 
     def view_folder_for_id(self, id_):
diff --git a/src/calibre/gui2/add.py b/src/calibre/gui2/add.py
index 1e440c9ffa..c28493ee59 100644
--- a/src/calibre/gui2/add.py
+++ b/src/calibre/gui2/add.py
@@ -14,7 +14,7 @@ from polyglot.builtins import iteritems, map, unicode_type, string_or_bytes
 from PyQt5.Qt import QObject, Qt, pyqtSignal
 
 from calibre import prints, as_unicode
-from calibre.constants import DEBUG, iswindows, isosx, filesystem_encoding
+from calibre.constants import DEBUG, iswindows, ismacos, filesystem_encoding
 from calibre.customize.ui import run_plugins_on_postimport, run_plugins_on_postadd
 from calibre.db.adding import find_books_in_directory, compile_rule
 from calibre.db.utils import find_identical_books
@@ -134,7 +134,7 @@ class Adder(QObject):
             import traceback
             traceback.print_exc()
 
-        if iswindows or isosx:
+        if iswindows or ismacos:
             def find_files(root):
                 for dirpath, dirnames, filenames in os.walk(root):
                     for files in find_books_in_directory(dirpath, self.single_book_per_directory, compiled_rules=compiled_rules):
diff --git a/src/calibre/gui2/bars.py b/src/calibre/gui2/bars.py
index f4aec49b84..17c4bf435a 100644
--- a/src/calibre/gui2/bars.py
+++ b/src/calibre/gui2/bars.py
@@ -15,7 +15,7 @@ try:
 except ImportError:
     import sip
 
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.gui2 import gprefs, native_menubar_defaults, config
 from calibre.gui2.throbber import ThrobbingButton
 from polyglot.builtins import itervalues, unicode_type, map, range
@@ -334,7 +334,7 @@ class MenuAction(QAction):  # {{{
 # MenuBar {{{
 
 
-if isosx:
+if ismacos:
     # On OS X we need special handling for the application global menu bar and
     # the context menus, since Qt does not handle dynamic menus or menus in
     # which the same action occurs in more than one place.
@@ -617,11 +617,11 @@ class AdaptMenuBarForDialog(object):
         self.menu_bar = menu_bar
 
     def __enter__(self):
-        if isosx and self.menu_bar.is_native_menubar:
+        if ismacos and self.menu_bar.is_native_menubar:
             self.menu_bar.adapt_for_dialog(True)
 
     def __exit__(self, *a):
-        if isosx and self.menu_bar.is_native_menubar:
+        if ismacos and self.menu_bar.is_native_menubar:
             self.menu_bar.adapt_for_dialog(False)
 
 
diff --git a/src/calibre/gui2/catalog/catalog_csv_xml.py b/src/calibre/gui2/catalog/catalog_csv_xml.py
index 903656ddb3..2a7319830e 100644
--- a/src/calibre/gui2/catalog/catalog_csv_xml.py
+++ b/src/calibre/gui2/catalog/catalog_csv_xml.py
@@ -8,7 +8,7 @@ __docformat__ = 'restructuredtext en'
 
 from PyQt5.Qt import QWidget, QListWidgetItem, Qt, QVBoxLayout, QLabel, QListWidget
 
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.gui2 import gprefs
 from calibre.gui2.ui import get_gui
 from polyglot.builtins import unicode_type, range
@@ -53,7 +53,7 @@ class PluginWidget(QWidget):
         l.addWidget(la)
         self.db_fields.setDragEnabled(True)
         self.db_fields.setDragDropMode(QListWidget.InternalMove)
-        self.db_fields.setDefaultDropAction(Qt.CopyAction if isosx else Qt.MoveAction)
+        self.db_fields.setDefaultDropAction(Qt.CopyAction if ismacos else Qt.MoveAction)
         self.db_fields.setAlternatingRowColors(True)
         self.db_fields.setObjectName("db_fields")
 
diff --git a/src/calibre/gui2/complete2.py b/src/calibre/gui2/complete2.py
index 7291f7e22d..f28232defa 100644
--- a/src/calibre/gui2/complete2.py
+++ b/src/calibre/gui2/complete2.py
@@ -15,7 +15,7 @@ try:
 except ImportError:
     import sip
 
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.utils.icu import sort_key, primary_startswith, primary_contains
 from calibre.gui2.widgets import EnComboBox, LineEditECM
 from calibre.utils.config import tweaks
@@ -250,7 +250,7 @@ class Completer(QListView):  # {{{
                 self.hide()
             if e.isAccepted():
                 return True
-        elif isosx and etype == e.InputMethodQuery and e.queries() == (Qt.ImHints | Qt.ImEnabled) and self.isVisible():
+        elif ismacos and etype == e.InputMethodQuery and e.queries() == (Qt.ImHints | Qt.ImEnabled) and self.isVisible():
             # In Qt 5 the Esc key causes this event and the line edit does not
             # handle it, which causes the parent dialog to be closed
             # See https://bugreports.qt-project.org/browse/QTBUG-41806
diff --git a/src/calibre/gui2/dbus_export/widgets.py b/src/calibre/gui2/dbus_export/widgets.py
index 9930d76ac1..0cfe34b790 100644
--- a/src/calibre/gui2/dbus_export/widgets.py
+++ b/src/calibre/gui2/dbus_export/widgets.py
@@ -10,7 +10,7 @@ import time, sys, weakref
 from PyQt5.Qt import (
     QObject, QMenuBar, QAction, QEvent, QSystemTrayIcon, QApplication, Qt)
 
-from calibre.constants import iswindows, isosx
+from calibre.constants import iswindows, ismacos
 from polyglot.builtins import range, unicode_type
 
 UNITY_WINDOW_REGISTRAR = ('com.canonical.AppMenu.Registrar', '/com/canonical/AppMenu/Registrar', 'com.canonical.AppMenu.Registrar')
@@ -117,7 +117,7 @@ class Factory(QObject):
     def __init__(self, app_id=None):
         QObject.__init__(self)
         self.app_id = app_id or QApplication.instance().applicationName() or 'unknown_application'
-        if iswindows or isosx:
+        if iswindows or ismacos:
             self.dbus = None
         else:
             try:
@@ -228,7 +228,7 @@ class Factory(QObject):
             self.prune_dead_refs()
             self.status_notifiers.append(weakref.ref(ans))
             return ans
-        if iswindows or isosx:
+        if iswindows or ismacos:
             return QSystemTrayIcon(parent)
 
     def bus_disconnected(self):
diff --git a/src/calibre/gui2/dialogs/plugin_updater.py b/src/calibre/gui2/dialogs/plugin_updater.py
index 1068cb0999..d71a8c32e9 100644
--- a/src/calibre/gui2/dialogs/plugin_updater.py
+++ b/src/calibre/gui2/dialogs/plugin_updater.py
@@ -15,7 +15,7 @@ from PyQt5.Qt import (Qt, QUrl, QFrame, QVBoxLayout, QLabel, QBrush, QTextEdit,
                       QFont, QPixmap, QSize, QLineEdit)
 
 from calibre import browser, prints
-from calibre.constants import numeric_version, iswindows, isosx, DEBUG, __appname__, __version__
+from calibre.constants import numeric_version, iswindows, ismacos, DEBUG, __appname__, __version__
 from calibre.customize.ui import (
     initialized_plugins, is_disabled, remove_plugin, add_plugin, enable_plugin, disable_plugin,
     NameConflict, has_external_plugins)
@@ -229,7 +229,7 @@ class DisplayPlugin(object):
     def is_valid_platform(self):
         if iswindows:
             return 'windows' in self.platforms
-        if isosx:
+        if ismacos:
             return 'osx' in self.platforms
         return 'linux' in self.platforms
 
diff --git a/src/calibre/gui2/init.py b/src/calibre/gui2/init.py
index aa174d45b4..29a52b86cf 100644
--- a/src/calibre/gui2/init.py
+++ b/src/calibre/gui2/init.py
@@ -14,7 +14,7 @@ from PyQt5.Qt import (
     QToolButton, QVBoxLayout, QWidget
 )
 
-from calibre.constants import __appname__, get_version, isosx
+from calibre.constants import __appname__, get_version, ismacos
 from calibre.customize.ui import find_plugin
 from calibre.gui2 import config, error_dialog, gprefs, is_widescreen, open_url
 from calibre.gui2.book_details import BookDetails
@@ -618,7 +618,7 @@ class LayoutMixin(object):  # {{{
                     button = self.search_bar_button
             self.layout_buttons.append(button)
             button.setVisible(False)
-            if isosx and stylename != 'Calibre':
+            if ismacos and stylename != 'Calibre':
                 button.setStyleSheet('''
                         QToolButton { background: none; border:none; padding: 0px; }
                         QToolButton:checked { background: rgba(0, 0, 0, 25%); }
diff --git a/src/calibre/gui2/main.py b/src/calibre/gui2/main.py
index 1805ac6ff4..a0fa608fae 100644
--- a/src/calibre/gui2/main.py
+++ b/src/calibre/gui2/main.py
@@ -16,7 +16,7 @@ from PyQt5.Qt import QCoreApplication, QIcon, QObject, QTimer
 from calibre import force_unicode, plugins, prints
 from calibre.constants import (
     DEBUG, MAIN_APP_UID, __appname__, filesystem_encoding, get_portable_base,
-    islinux, isosx, iswindows
+    islinux, ismacos, iswindows
 )
 from calibre.gui2 import (
     Application, choose_dir, error_dialog, gprefs, initialize_file_icon_provider,
@@ -382,7 +382,7 @@ def run_gui(opts, args, listener, app, gui_debug=None):
         wizard().exec_()
         dynamic.set('welcome_wizard_was_run', True)
     from calibre.gui2.ui import Main
-    if isosx:
+    if ismacos:
         actions = tuple(Main.create_application_menubar())
     else:
         actions = tuple(Main.get_menubar_actions())
@@ -446,7 +446,7 @@ def cant_start(msg=_('If you are sure it is not running')+', ',
                listener_failed=False):
     base = '<p>%s</p><p>%s %s'
     where = __appname__ + ' '+_('may be running in the system tray, in the')+' '
-    if isosx:
+    if ismacos:
         where += _('upper right region of the screen.')
     else:
         where += _('lower right region of the screen.')
diff --git a/src/calibre/gui2/metadata/single.py b/src/calibre/gui2/metadata/single.py
index f3de859ef9..d3ceb2a812 100644
--- a/src/calibre/gui2/metadata/single.py
+++ b/src/calibre/gui2/metadata/single.py
@@ -15,7 +15,7 @@ from PyQt5.Qt import (Qt, QVBoxLayout, QHBoxLayout, QWidget, QPushButton, QAppli
         QTabWidget, QIcon, QToolButton, QSplitter, QGroupBox, QSpacerItem, QInputDialog,
         QSizePolicy, QFrame, QSize, QKeySequence, QMenu, QShortcut, QDialog)
 
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.gui2.dialogs.confirm_delete import confirm
 from calibre.ebooks.metadata import authors_to_string, string_to_authors
 from calibre.gui2 import error_dialog, gprefs, pixmap_to_data
@@ -158,7 +158,7 @@ class MetadataSingleDialogBase(QDialog):
               'change author sort from red to green.  There is a menu of '
               'functions available under this button. Click and hold '
               'on the button to see it.') + '</p>')
-        if isosx:
+        if ismacos:
             # Workaround for https://bugreports.qt-project.org/browse/QTBUG-41017
             class Menu(QMenu):
 
diff --git a/src/calibre/gui2/notify.py b/src/calibre/gui2/notify.py
index 84653b1940..dba7be8ba8 100644
--- a/src/calibre/gui2/notify.py
+++ b/src/calibre/gui2/notify.py
@@ -9,7 +9,7 @@ __docformat__ = 'restructuredtext en'
 
 import time
 from calibre import prints
-from calibre.constants import islinux, isosx, get_osx_version, DEBUG, plugins
+from calibre.constants import islinux, ismacos, get_osx_version, DEBUG, plugins
 from polyglot.builtins import unicode_type
 
 
@@ -109,7 +109,7 @@ class QtNotifier(Notifier):
                 try:
                     if not isinstance(body, unicode_type):
                         body = body.decode('utf-8')
-                    if isosx and not self.systray.isVisible():
+                    if ismacos and not self.systray.isVisible():
                         self.systray.show()
                         hide = True
                     self.systray.showMessage(summary, body, self.systray.Information,
@@ -161,7 +161,7 @@ def get_notifier(systray=None):
             import traceback
             traceback.print_exc()
             ans = None
-    elif isosx:
+    elif ismacos:
         if get_osx_version() >= (10, 8, 0):
             ans = AppleNotifier()
             if not ans.ok:
diff --git a/src/calibre/gui2/open_with.py b/src/calibre/gui2/open_with.py
index 66388a1f50..912a7caf74 100644
--- a/src/calibre/gui2/open_with.py
+++ b/src/calibre/gui2/open_with.py
@@ -15,7 +15,7 @@ from PyQt5.Qt import (
     QBuffer, QPixmap, QAction, QKeySequence)
 
 from calibre import as_unicode
-from calibre.constants import iswindows, isosx
+from calibre.constants import iswindows, ismacos
 from calibre.gui2 import error_dialog, choose_files, choose_images, elided_text, sanitize_env_vars, Application, choose_osx_app
 from calibre.gui2.widgets2 import Dialog
 from calibre.gui2.progress_indicator import ProgressIndicator
@@ -146,7 +146,7 @@ if iswindows:
                 det_msg='Command line: %r\n%s' %(cmdline, as_unicode(err)))
     # }}}
 
-elif isosx:
+elif ismacos:
     # macOS {{{
     oprefs = JSONConfig('osx_open_with')
     from calibre.utils.open_with.osx import find_programs, get_icon, entry_to_cmdline, get_bundle_data
diff --git a/src/calibre/gui2/preferences/look_feel.py b/src/calibre/gui2/preferences/look_feel.py
index 141b20dc4d..0eafe6e948 100644
--- a/src/calibre/gui2/preferences/look_feel.py
+++ b/src/calibre/gui2/preferences/look_feel.py
@@ -20,7 +20,7 @@ from PyQt5.Qt import (
 
 from calibre import human_readable
 from calibre.ebooks.metadata.book.render import DEFAULT_AUTHOR_LINK
-from calibre.constants import isosx, iswindows
+from calibre.constants import ismacos, iswindows
 from calibre.ebooks.metadata.sources.prefs import msprefs
 from calibre.gui2 import default_author_link
 from calibre.gui2.dialogs.template_dialog import TemplateDialog
@@ -383,7 +383,7 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
 
     def genesis(self, gui):
         self.gui = gui
-        if not isosx and not iswindows:
+        if not ismacos and not iswindows:
             self.label_widget_style.setVisible(False)
             self.opt_ui_style.setVisible(False)
 
@@ -402,7 +402,7 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
         self.default_author_link.changed_signal.connect(self.changed_signal)
         r('gui_layout', config, restart_required=True, choices=[(_('Wide'), 'wide'), (_('Narrow'), 'narrow')])
         r('hidpi', gprefs, restart_required=True, choices=[(_('Automatic'), 'auto'), (_('On'), 'on'), (_('Off'), 'off')])
-        if isosx:
+        if ismacos:
             self.opt_hidpi.setVisible(False), self.label_hidpi.setVisible(False)
         r('ui_style', gprefs, restart_required=True, choices=[(_('System default'), 'system'), (_('calibre style'), 'calibre')])
         r('book_list_tooltips', gprefs)
diff --git a/src/calibre/gui2/tweak_book/editor/snippets.py b/src/calibre/gui2/tweak_book/editor/snippets.py
index 50a735f2af..3d6b3c6e7b 100644
--- a/src/calibre/gui2/tweak_book/editor/snippets.py
+++ b/src/calibre/gui2/tweak_book/editor/snippets.py
@@ -15,7 +15,7 @@ from PyQt5.Qt import (
     QToolButton, QIcon, QHBoxLayout, QPushButton, QListWidget, QListWidgetItem,
     QGridLayout, QPlainTextEdit, QLabel, QFrame, QDialog, QDialogButtonBox)
 
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.gui2 import error_dialog
 from calibre.gui2.tweak_book.editor import all_text_syntaxes
 from calibre.gui2.tweak_book.editor.smarts.utils import get_text_before_cursor
@@ -27,7 +27,7 @@ from polyglot.builtins import codepoint_to_chr, iteritems, itervalues, unicode_t
 
 string_length = lambda x: strlen(unicode_type(x))  # Needed on narrow python builds, as subclasses of unicode dont work
 KEY = Qt.Key_J
-MODIFIER = Qt.META if isosx else Qt.CTRL
+MODIFIER = Qt.META if ismacos else Qt.CTRL
 
 SnipKey = namedtuple('SnipKey', 'trigger syntaxes')
 
diff --git a/src/calibre/gui2/tweak_book/ui.py b/src/calibre/gui2/tweak_book/ui.py
index ef1f4750e5..a820e8065a 100644
--- a/src/calibre/gui2/tweak_book/ui.py
+++ b/src/calibre/gui2/tweak_book/ui.py
@@ -16,7 +16,7 @@ from PyQt5.Qt import (
     QMenu, QHBoxLayout, QTimer, QUrl, QSize)
 
 from calibre import prints
-from calibre.constants import __appname__, get_version, isosx, DEBUG
+from calibre.constants import __appname__, get_version, ismacos, DEBUG
 from calibre.customize.ui import find_plugin
 from calibre.gui2 import elided_text, open_url
 from calibre.gui2.dbus_export.widgets import factory
@@ -357,9 +357,9 @@ class Main(MainWindow):
                 'edit-previous-file', 'Ctrl+Alt+Up', _('Edit the previous file in the spine'))
         # Qt does not generate shortcut overrides for cmd+arrow on os x which
         # means these shortcuts interfere with editing
-        self.action_global_undo = treg('back.png', _('&Revert to before'), self.boss.do_global_undo, 'global-undo', () if isosx else 'Ctrl+Left',
+        self.action_global_undo = treg('back.png', _('&Revert to before'), self.boss.do_global_undo, 'global-undo', () if ismacos else 'Ctrl+Left',
                                       _('Revert book to before the last action (Undo)'))
-        self.action_global_redo = treg('forward.png', _('&Revert to after'), self.boss.do_global_redo, 'global-redo', () if isosx else 'Ctrl+Right',
+        self.action_global_redo = treg('forward.png', _('&Revert to after'), self.boss.do_global_redo, 'global-redo', () if ismacos else 'Ctrl+Right',
                                       _('Revert book state to after the next action (Redo)'))
         self.action_save = treg('save.png', _('&Save'), self.boss.save_book, 'save-book', 'Ctrl+S', _('Save book'))
         self.action_save.setEnabled(False)
@@ -531,7 +531,7 @@ class Main(MainWindow):
         create_plugin_actions(actions, toolbar_actions, self.plugin_menu_actions)
 
     def create_menubar(self):
-        if isosx:
+        if ismacos:
             p, q = self.create_application_menubar()
             q.triggered.connect(self.action_quit.trigger)
             p.triggered.connect(self.action_preferences.trigger)
diff --git a/src/calibre/gui2/ui.py b/src/calibre/gui2/ui.py
index 2f6b06896a..b3618b55ed 100644
--- a/src/calibre/gui2/ui.py
+++ b/src/calibre/gui2/ui.py
@@ -21,7 +21,7 @@ from PyQt5.Qt import (
 
 from calibre import prints, force_unicode, detect_ncpus
 from calibre.constants import (
-        __appname__, isosx, iswindows, filesystem_encoding, DEBUG, config_dir)
+        __appname__, ismacos, iswindows, filesystem_encoding, DEBUG, config_dir)
 from calibre.utils.config import prefs, dynamic
 from calibre.utils.ipc.pool import Pool
 from calibre.db.legacy import LibraryDatabase
@@ -271,7 +271,7 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
             self.system_tray_icon = factory(app_id='com.calibre-ebook.gui').create_system_tray_icon(parent=self, title='calibre')
         if self.system_tray_icon is not None:
             self.system_tray_icon.setIcon(QIcon(I('lt.png', allow_user_override=False)))
-            if not (iswindows or isosx):
+            if not (iswindows or ismacos):
                 self.system_tray_icon.setIcon(QIcon.fromTheme('calibre-tray', self.system_tray_icon.icon()))
             self.system_tray_icon.setToolTip(self.jobs_button.tray_tooltip())
             self.system_tray_icon.setVisible(True)
@@ -1069,7 +1069,7 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
             return
         self.write_settings()
         if self.system_tray_icon is not None and self.system_tray_icon.isVisible():
-            if not dynamic['systray_msg'] and not isosx:
+            if not dynamic['systray_msg'] and not ismacos:
                 info_dialog(self, 'calibre', 'calibre '+
                         _('will keep running in the system tray. To close it, '
                         'choose <b>Quit</b> in the context menu of the '
diff --git a/src/calibre/gui2/update.py b/src/calibre/gui2/update.py
index 9576b6443b..d44d7d0734 100644
--- a/src/calibre/gui2/update.py
+++ b/src/calibre/gui2/update.py
@@ -9,7 +9,7 @@ from threading import Thread, Event
 from PyQt5.Qt import (QObject, pyqtSignal, Qt, QUrl, QDialog, QGridLayout,
         QLabel, QCheckBox, QDialogButtonBox, QIcon)
 
-from calibre.constants import (__appname__, __version__, iswindows, isosx,
+from calibre.constants import (__appname__, __version__, iswindows, ismacos,
         isportable, is64bit, numeric_version)
 from calibre import prints, as_unicode
 from calibre.utils.config import prefs
@@ -28,7 +28,7 @@ NO_CALIBRE_UPDATE = (0, 0, 0)
 
 def get_download_url():
     which = ('portable' if isportable else 'windows' if iswindows
-            else 'osx' if isosx else 'linux')
+            else 'osx' if ismacos else 'linux')
     if which == 'windows' and is64bit:
         which += '64'
     return localize_website_link('https://calibre-ebook.com/download_' + which)
@@ -41,7 +41,7 @@ def get_newest_version():
         icon_theme_name = ''
     headers={
         'CALIBRE-VERSION':__version__,
-        'CALIBRE-OS': ('win' if iswindows else 'osx' if isosx else 'oth'),
+        'CALIBRE-OS': ('win' if iswindows else 'osx' if ismacos else 'oth'),
         'CALIBRE-INSTALL-UUID': prefs['installation_uuid'],
         'CALIBRE-ICON-THEME': icon_theme_name,
     }
diff --git a/src/calibre/gui2/viewer/toolbars.py b/src/calibre/gui2/viewer/toolbars.py
index 6ff496b317..88b8660856 100644
--- a/src/calibre/gui2/viewer/toolbars.py
+++ b/src/calibre/gui2/viewer/toolbars.py
@@ -12,7 +12,7 @@ from PyQt5.Qt import (
 )
 from PyQt5.QtWebEngineWidgets import QWebEnginePage
 
-from calibre.constants import isosx
+from calibre.constants import ismacos
 from calibre.gui2 import elided_text
 from calibre.gui2.viewer.config import get_session_pref
 from calibre.gui2.viewer.shortcuts import index_to_key_sequence
@@ -313,7 +313,7 @@ class ActionsList(QListWidget):
         self.viewport().setAcceptDrops(True)
         self.setDropIndicatorShown(True)
         self.setDragDropMode(self.InternalMove)
-        self.setDefaultDropAction(Qt.CopyAction if isosx else Qt.MoveAction)
+        self.setDefaultDropAction(Qt.CopyAction if ismacos else Qt.MoveAction)
         self.setMinimumHeight(400)
         self.is_source = is_source
         if is_source:
diff --git a/src/calibre/gui2/viewer/web_view.py b/src/calibre/gui2/viewer/web_view.py
index dfa4791394..7006fa9f1c 100644
--- a/src/calibre/gui2/viewer/web_view.py
+++ b/src/calibre/gui2/viewer/web_view.py
@@ -20,7 +20,7 @@ from PyQt5.QtWebEngineWidgets import (
 from calibre import as_unicode, prints
 from calibre.constants import (
     FAKE_HOST, FAKE_PROTOCOL, __version__, in_develop_mode, is_running_from_develop,
-    isosx, iswindows
+    ismacos, iswindows
 )
 from calibre.ebooks.metadata.book.base import field_metadata
 from calibre.ebooks.oeb.polish.utils import guess_type
@@ -204,7 +204,7 @@ def create_profile():
     ans = getattr(create_profile, 'ans', None)
     if ans is None:
         ans = QWebEngineProfile(QApplication.instance())
-        osname = 'windows' if iswindows else ('macos' if isosx else 'linux')
+        osname = 'windows' if iswindows else ('macos' if ismacos else 'linux')
         # DO NOT change the user agent as it is used to workaround
         # Qt bugs see workaround_qt_bug() in ajax.pyj
         ua = 'calibre-viewer {} {}'.format(__version__, osname)
diff --git a/src/calibre/gui2/widgets.py b/src/calibre/gui2/widgets.py
index 583b306b32..92838d637e 100644
--- a/src/calibre/gui2/widgets.py
+++ b/src/calibre/gui2/widgets.py
@@ -14,7 +14,7 @@ from PyQt5.Qt import (QIcon, QFont, QLabel, QListWidget, QAction,
         QLineEdit, QComboBox, QPen, QGraphicsScene, QMenu, QStringListModel,
         QCompleter, QTimer, QRect, QGraphicsView, QPagedPaintDevice)
 
-from calibre.constants import iswindows, isosx
+from calibre.constants import iswindows, ismacos
 from calibre.gui2 import (error_dialog, pixmap_to_data, gprefs,
         warning_dialog)
 from calibre.gui2.filename_pattern_ui import Ui_Form
@@ -1249,7 +1249,7 @@ class PaperSizes(QComboBox):  # {{{
         from calibre.utils.icu import numeric_sort_key
         if self.system_default_paper_size is None:
             PaperSizes.system_default_paper_size = 'a4'
-            if iswindows or isosx:
+            if iswindows or ismacos:
                 # On Linux, this can cause Qt to load the system cups plugin
                 # which can crash: https://bugs.launchpad.net/calibre/+bug/1861741
                 PaperSizes.system_default_paper_size = 'letter' if QPrinter().pageSize() == QPagedPaintDevice.Letter else 'a4'
diff --git a/src/calibre/library/catalogs/epub_mobi_builder.py b/src/calibre/library/catalogs/epub_mobi_builder.py
index 494c786aa6..260372aac2 100644
--- a/src/calibre/library/catalogs/epub_mobi_builder.py
+++ b/src/calibre/library/catalogs/epub_mobi_builder.py
@@ -20,7 +20,7 @@ from calibre import (
     as_unicode, force_unicode, isbytestring, prepare_string_for_xml,
     replace_entities, strftime, xml_replace_entities
 )
-from calibre.constants import cache_dir, isosx
+from calibre.constants import cache_dir, ismacos
 from calibre.utils.xml_parse import safe_xml_fromstring
 from calibre.customize.conversion import DummyReporter
 from calibre.customize.ui import output_profiles
@@ -706,7 +706,7 @@ class CatalogBuilder(object):
                 c = item
 
             ordnum, ordlen = collation_order(c)
-            if isosx and platform.mac_ver()[0] < '10.8':
+            if ismacos and platform.mac_ver()[0] < '10.8':
                 # Hackhackhackhackhack
                 # icu returns bogus results with curly apostrophes, maybe others under OS X 10.6.x
                 # When we see the magic combo of 0/-1 for ordnum/ordlen, special case the logic
diff --git a/src/calibre/ptempfile.py b/src/calibre/ptempfile.py
index cf7d69b85e..b59595a69a 100644
--- a/src/calibre/ptempfile.py
+++ b/src/calibre/ptempfile.py
@@ -9,7 +9,7 @@ import tempfile, os, atexit
 from polyglot.builtins import map, getenv
 
 from calibre.constants import (__version__, __appname__, filesystem_encoding,
-        iswindows, get_windows_temp_path, isosx)
+        iswindows, get_windows_temp_path, ismacos)
 
 
 def cleanup(path):
@@ -113,7 +113,7 @@ def base_dir():
                     # unicode temp path instead. See
                     # https://bugs.launchpad.net/bugs/937389
                     base = get_windows_temp_path()
-                elif isosx:
+                elif ismacos:
                     # Use the cache dir rather than the temp dir for temp files as Apple
                     # thinks deleting unused temp files is a good idea. See note under
                     # _CS_DARWIN_USER_TEMP_DIR here
diff --git a/src/calibre/srv/auto_reload.py b/src/calibre/srv/auto_reload.py
index 3001dfd573..cef58e1377 100644
--- a/src/calibre/srv/auto_reload.py
+++ b/src/calibre/srv/auto_reload.py
@@ -8,7 +8,7 @@ __copyright__ = '2015, Kovid Goyal <kovid at kovidgoyal.net>'
 import os, sys, subprocess, signal, time, errno, socket, ssl
 from threading import Thread, Lock
 
-from calibre.constants import islinux, iswindows, isosx
+from calibre.constants import islinux, iswindows, ismacos
 from calibre.srv.http_response import create_http_handler
 from calibre.srv.loop import ServerLoop
 from calibre.srv.opts import Options
@@ -161,7 +161,7 @@ elif iswindows:
                     else:
                         self.handle_modified({path})
 
-elif isosx:
+elif ismacos:
     from fsevents import Observer, Stream
 
     class Watcher(WatcherBase):
diff --git a/src/calibre/srv/sendfile.py b/src/calibre/srv/sendfile.py
index d3fbbd5c2f..49beff15ff 100644
--- a/src/calibre/srv/sendfile.py
+++ b/src/calibre/srv/sendfile.py
@@ -9,7 +9,7 @@ import os, ctypes, errno, socket
 from io import DEFAULT_BUFFER_SIZE
 from select import select
 
-from calibre.constants import islinux, isosx
+from calibre.constants import islinux, ismacos
 from calibre.srv.utils import eintr_retry_call
 
 
@@ -45,7 +45,7 @@ class SendfileInterrupted(Exception):
 
 sendfile_to_socket = sendfile_to_socket_async = None
 
-if isosx:
+if ismacos:
     libc = ctypes.CDLL(None, use_errno=True)
     sendfile = ctypes.CFUNCTYPE(
         ctypes.c_int, ctypes.c_int, ctypes.c_int, ctypes.c_int64, ctypes.POINTER(ctypes.c_int64), ctypes.c_void_p, ctypes.c_int, use_errno=True)(
diff --git a/src/calibre/srv/standalone.py b/src/calibre/srv/standalone.py
index 8d38e1ea0a..b635c5b3f7 100644
--- a/src/calibre/srv/standalone.py
+++ b/src/calibre/srv/standalone.py
@@ -9,7 +9,7 @@ import signal
 import sys
 
 from calibre import as_unicode
-from calibre.constants import is_running_from_develop, isosx, iswindows, plugins
+from calibre.constants import is_running_from_develop, ismacos, iswindows, plugins
 from calibre.db.delete_service import shutdown as shutdown_delete_service
 from calibre.db.legacy import LibraryDatabase
 from calibre.srv.bonjour import BonJour
@@ -129,7 +129,7 @@ libraries that the main calibre program knows about will be used.
             ' URLs and export them.'
     ))
 
-    if not iswindows and not isosx:
+    if not iswindows and not ismacos:
         # Does not work on macOS because if we fork() we cannot connect to Core
         # Serives which is needed by the QApplication() constructor, which in
         # turn is needed by ensure_app()
diff --git a/src/calibre/startup.py b/src/calibre/startup.py
index a924576e5b..731afff32f 100644
--- a/src/calibre/startup.py
+++ b/src/calibre/startup.py
@@ -21,7 +21,7 @@ builtins.__dict__['__'] = lambda s: s
 builtins.__dict__['dynamic_property'] = lambda func: func(None)
 
 
-from calibre.constants import iswindows, preferred_encoding, plugins, isosx, islinux, DEBUG, isfreebsd
+from calibre.constants import iswindows, preferred_encoding, plugins, ismacos, islinux, DEBUG, isfreebsd
 
 _run_once = False
 winutil = winutilerror = None
@@ -100,7 +100,7 @@ if not _run_once:
     #
     # Convert command line arguments to unicode
     enc = preferred_encoding
-    if isosx:
+    if ismacos:
         enc = 'utf-8'
     for i in range(1, len(sys.argv)):
         if not isinstance(sys.argv[i], unicode_type):
@@ -199,7 +199,7 @@ if not _run_once:
         bound_signal.connect(slot, **kw)
     builtins.__dict__['connect_lambda'] = connect_lambda
 
-    if islinux or isosx or isfreebsd:
+    if islinux or ismacos or isfreebsd:
         # Name all threads at the OS level created using the threading module, see
         # http://bugs.python.org/issue15500
         import threading
diff --git a/src/calibre/test_build.py b/src/calibre/test_build.py
index 935a122080..fd794713b8 100644
--- a/src/calibre/test_build.py
+++ b/src/calibre/test_build.py
@@ -12,7 +12,7 @@ Test a binary calibre build to ensure that all needed binary images/libraries ha
 
 import os, ctypes, sys, unittest, time
 
-from calibre.constants import plugins, iswindows, islinux, isosx, plugins_loc
+from calibre.constants import plugins, iswindows, islinux, ismacos, plugins_loc
 from polyglot.builtins import iteritems, map, unicode_type, getenv, native_string_type
 
 is_ci = os.environ.get('CI', '').lower() == 'true'
@@ -100,7 +100,7 @@ class BuildTest(unittest.TestCase):
             if name in exclusions:
                 if name in ('libusb', 'libmtp'):
                     # Just check that the DLL can be loaded
-                    ctypes.CDLL(os.path.join(plugins_loc, name + ('.dylib' if isosx else '.so')))
+                    ctypes.CDLL(os.path.join(plugins_loc, name + ('.dylib' if ismacos else '.so')))
                 continue
             mod, err = plugins[name]
             self.assertFalse(err or not mod, 'Failed to load plugin: ' + name + ' with error:\n' + err)
@@ -128,7 +128,7 @@ class BuildTest(unittest.TestCase):
         large = b'x' * (100 * 1024 * 1024)
         msgpack_loads(msgpack_dumps(large))
 
-    @unittest.skipUnless(isosx, 'FSEvents only present on OS X')
+    @unittest.skipUnless(ismacos, 'FSEvents only present on OS X')
     def test_fsevents(self):
         from fsevents import Observer, Stream
         del Observer, Stream
@@ -235,7 +235,7 @@ class BuildTest(unittest.TestCase):
             p.printToPdf(print_callback)
             QTimer.singleShot(5000, lambda: QApplication.instance().quit())
             QApplication.instance().exec_()
-            test_flaky = isosx and not is_ci
+            test_flaky = ismacos and not is_ci
             if not test_flaky:
                 self.assertEqual(callback.result, 2, 'Simple JS computation failed')
                 self.assertIn(b'Skia/PDF', bytes(print_callback.result), 'Print to PDF failed')
@@ -334,7 +334,7 @@ class BuildTest(unittest.TestCase):
     def test_openssl(self):
         import ssl
         ssl.PROTOCOL_TLSv1_2
-        if isosx:
+        if ismacos:
             cafile = ssl.get_default_verify_paths().cafile
             if not cafile or not cafile.endswith('/mozilla-ca-certs.pem') or not os.access(cafile, os.R_OK):
                 raise AssertionError('Mozilla CA certs not loaded')
diff --git a/src/calibre/utils/date.py b/src/calibre/utils/date.py
index 3d84d2ee82..c877bebcb3 100644
--- a/src/calibre/utils/date.py
+++ b/src/calibre/utils/date.py
@@ -11,7 +11,7 @@ from datetime import datetime, time as dtime, timedelta, MINYEAR, MAXYEAR
 from functools import partial
 
 from calibre import strftime
-from calibre.constants import iswindows, isosx, plugins, preferred_encoding
+from calibre.constants import iswindows, ismacos, plugins, preferred_encoding
 from calibre.utils.iso8601 import utc_tz, local_tz, UNDEFINED_DATE
 from calibre.utils.localization import lcdata
 from polyglot.builtins import unicode_type, native_string_type
@@ -31,7 +31,7 @@ if iswindows:
     except:
         parse_date_day_first = False
     del ctypes, LOCALE_SSHORTDATE, buf, LOCALE_USER_DEFAULT
-elif isosx:
+elif ismacos:
     try:
         date_fmt = plugins['usbobserver'][0].date_format()
         parse_date_day_first = date_fmt.index('d') < date_fmt.index('M')
diff --git a/src/calibre/utils/filenames.py b/src/calibre/utils/filenames.py
index 2687bb2862..6ba5dbbedf 100644
--- a/src/calibre/utils/filenames.py
+++ b/src/calibre/utils/filenames.py
@@ -12,7 +12,7 @@ from math import ceil
 
 from calibre import force_unicode, isbytestring, prints, sanitize_file_name
 from calibre.constants import (
-    filesystem_encoding, iswindows, plugins, preferred_encoding, isosx
+    filesystem_encoding, iswindows, plugins, preferred_encoding, ismacos
 )
 from calibre.utils.localization import get_udc
 from polyglot.builtins import iteritems, itervalues, unicode_type, range
@@ -52,7 +52,7 @@ def shorten_component(s, by_what):
 def limit_component(x, limit=254):
     # windows and macs use ytf-16 codepoints for length, linux uses arbitrary
     # binary data, but we will assume utf-8
-    filename_encoding_for_length = 'utf-16' if iswindows or isosx else 'utf-8'
+    filename_encoding_for_length = 'utf-16' if iswindows or ismacos else 'utf-8'
 
     def encoded_length():
         q = x if isinstance(x, bytes) else x.encode(filename_encoding_for_length)
diff --git a/src/calibre/utils/fonts/scanner.py b/src/calibre/utils/fonts/scanner.py
index 0092072b3f..94baa9312d 100644
--- a/src/calibre/utils/fonts/scanner.py
+++ b/src/calibre/utils/fonts/scanner.py
@@ -11,7 +11,7 @@ from collections import defaultdict
 from threading import Thread
 
 from calibre import walk, prints, as_unicode
-from calibre.constants import (config_dir, iswindows, isosx, plugins, DEBUG,
+from calibre.constants import (config_dir, iswindows, ismacos, plugins, DEBUG,
         isworker, filesystem_encoding)
 from calibre.utils.fonts.metadata import FontMetadata, UnsupportedFont
 from calibre.utils.icu import sort_key
@@ -113,7 +113,7 @@ def font_dirs():
                 path = os.path.join(path, r'Microsoft\Windows\Fonts')
             paths.add(os.path.normcase(path))
         return list(paths)
-    if isosx:
+    if ismacos:
         return [
                 '/Library/Fonts',
                 '/System/Library/Fonts',
diff --git a/src/calibre/utils/ip_routing.py b/src/calibre/utils/ip_routing.py
index e533df137d..a945402bf8 100644
--- a/src/calibre/utils/ip_routing.py
+++ b/src/calibre/utils/ip_routing.py
@@ -4,7 +4,7 @@
 
 
 import subprocess, re
-from calibre.constants import iswindows, isosx
+from calibre.constants import iswindows, ismacos
 
 
 def get_address_of_default_gateway(family='AF_INET'):
@@ -56,7 +56,7 @@ if iswindows:
     get_default_route_src_address = get_default_route_src_address_api
 
 
-elif isosx:
+elif ismacos:
 
     def get_default_route_src_address():
         # Use -inet6 for IPv6
diff --git a/src/calibre/utils/ipc/launch.py b/src/calibre/utils/ipc/launch.py
index 71a42a0234..a555e0fca0 100644
--- a/src/calibre/utils/ipc/launch.py
+++ b/src/calibre/utils/ipc/launch.py
@@ -7,7 +7,7 @@ __docformat__ = 'restructuredtext en'
 
 import subprocess, os, sys, time
 
-from calibre.constants import iswindows, isosx, isfrozen
+from calibre.constants import iswindows, ismacos, isfrozen
 from calibre.utils.config import prefs
 from calibre.ptempfile import PersistentTemporaryFile, base_dir
 from calibre.utils.serialize import msgpack_dumps
@@ -56,7 +56,7 @@ class Worker(object):
         if iswindows:
             return os.path.join(os.path.dirname(sys.executable),
                    e+'.exe' if isfrozen else 'Scripts\\%s.exe'%e)
-        if isosx:
+        if ismacos:
             return os.path.join(sys.executables_location, e)
 
         if isfrozen:
@@ -70,7 +70,7 @@ class Worker(object):
 
     @property
     def gui_executable(self):
-        if isosx and not hasattr(sys, 'running_from_setup'):
+        if ismacos and not hasattr(sys, 'running_from_setup'):
             if self.job_name == 'ebook-viewer':
                 base = os.path.dirname(sys.executables_location)
                 return os.path.join(base, 'ebook-viewer.app/Contents/MacOS/', self.exe_name)
diff --git a/src/calibre/utils/ipc/worker.py b/src/calibre/utils/ipc/worker.py
index d10e968e62..13aecbaf16 100644
--- a/src/calibre/utils/ipc/worker.py
+++ b/src/calibre/utils/ipc/worker.py
@@ -13,7 +13,7 @@ from contextlib import closing
 from zipimport import ZipImportError
 
 from calibre import prints
-from calibre.constants import iswindows, isosx
+from calibre.constants import iswindows, ismacos
 from calibre.utils.ipc import eintr_retry_call
 from calibre.utils.serialize import msgpack_loads, pickle_dumps
 from polyglot.queue import Queue
@@ -171,7 +171,7 @@ def main():
         # Close open file descriptors inherited from parent
         # On Unix this is done by the subprocess module
         os.closerange(3, 256)
-    if isosx and 'CALIBRE_WORKER_ADDRESS' not in os.environ and 'CALIBRE_SIMPLE_WORKER' not in os.environ and '--pipe-worker' not in sys.argv:
+    if ismacos and 'CALIBRE_WORKER_ADDRESS' not in os.environ and 'CALIBRE_SIMPLE_WORKER' not in os.environ and '--pipe-worker' not in sys.argv:
         # On some OS X computers launchd apparently tries to
         # launch the last run process from the bundle
         # so launch the gui as usual
diff --git a/src/calibre/utils/localization.py b/src/calibre/utils/localization.py
index 7030bd4eeb..6874f39ca0 100644
--- a/src/calibre/utils/localization.py
+++ b/src/calibre/utils/localization.py
@@ -29,7 +29,7 @@ def available_translations():
 
 
 def get_system_locale():
-    from calibre.constants import iswindows, isosx, plugins
+    from calibre.constants import iswindows, ismacos, plugins
     lang = None
     if iswindows:
         try:
@@ -40,7 +40,7 @@ def get_system_locale():
                 lang = None
         except:
             pass  # Windows XP does not have the GetUserDefaultLocaleName fn
-    elif isosx:
+    elif ismacos:
         try:
             lang = plugins['usbobserver'][0].user_locale() or None
         except:
diff --git a/src/calibre/utils/lock.py b/src/calibre/utils/lock.py
index ba697d727f..7c3803aef4 100644
--- a/src/calibre/utils/lock.py
+++ b/src/calibre/utils/lock.py
@@ -11,7 +11,7 @@ import time
 from functools import partial
 
 from calibre.constants import (
-    __appname__, fcntl, filesystem_encoding, islinux, isosx, iswindows, plugins
+    __appname__, fcntl, filesystem_encoding, islinux, ismacos, iswindows, plugins
 )
 from calibre.utils.monotonic import monotonic
 from calibre.utils.shared_file import raise_winerror
@@ -172,7 +172,7 @@ else:
         )
         home = os.path.expanduser('~')
         locs = ['/var/lock', home, tempfile.gettempdir()]
-        if isosx:
+        if ismacos:
             locs.insert(0, '/Library/Caches')
         for loc in locs:
             if os.access(loc, os.W_OK | os.R_OK | os.X_OK):
diff --git a/src/calibre/utils/recycle_bin.py b/src/calibre/utils/recycle_bin.py
index 7f505b49d9..6f2742ebc8 100644
--- a/src/calibre/utils/recycle_bin.py
+++ b/src/calibre/utils/recycle_bin.py
@@ -9,7 +9,7 @@ __docformat__ = 'restructuredtext en'
 import os, shutil, time, sys
 
 from calibre import isbytestring
-from calibre.constants import (iswindows, isosx, plugins, filesystem_encoding,
+from calibre.constants import (iswindows, ismacos, plugins, filesystem_encoding,
         islinux)
 from polyglot.builtins import unicode_type
 
@@ -85,7 +85,7 @@ if iswindows:
         path = os.path.abspath(path)  # Windows does not like recycling relative paths
         return delegate_recycle(path)
 
-elif isosx:
+elif ismacos:
     u = plugins['cocoa'][0]
     if hasattr(u, 'send2trash'):
         def osx_recycle(path):