diff --git a/src/calibre/customize/zipplugin.py b/src/calibre/customize/zipplugin.py
index f68f2095b6..763a2221f4 100644
--- a/src/calibre/customize/zipplugin.py
+++ b/src/calibre/customize/zipplugin.py
@@ -19,7 +19,7 @@ from importlib.util import decode_source
 
 from calibre import as_unicode
 from calibre.customize import InvalidPlugin, Plugin, PluginNotFound, numeric_version, platform
-from polyglot.builtins import reload, string_or_bytes
+from polyglot.builtins import reload
 
 
 def get_resources(zfp, name_or_list_of_names, print_tracebacks_for_missing_resources=True):
@@ -37,7 +37,7 @@ def get_resources(zfp, name_or_list_of_names, print_tracebacks_for_missing_resou
                 be just the bytes of the resource or None if it wasn't found.
     '''
     names = name_or_list_of_names
-    if isinstance(names, string_or_bytes):
+    if isinstance(names, (str, bytes)):
         names = [names]
     ans = {}
     with zipfile.ZipFile(zfp) as zf:
@@ -74,7 +74,7 @@ def get_icons(zfp, name_or_list_of_names, plugin_name='', print_tracebacks_for_m
     '''
     from qt.core import QIcon, QPixmap
     ans = {}
-    namelist = [name_or_list_of_names] if isinstance(name_or_list_of_names, string_or_bytes) else name_or_list_of_names
+    namelist = [name_or_list_of_names] if isinstance(name_or_list_of_names, (str, bytes)) else name_or_list_of_names
     failed = set()
     if plugin_name:
         for name in namelist:
@@ -89,7 +89,7 @@ def get_icons(zfp, name_or_list_of_names, plugin_name='', print_tracebacks_for_m
         from_zfp = get_resources(zfp, list(failed), print_tracebacks_for_missing_resources=print_tracebacks_for_missing_resources)
         if from_zfp is None:
             from_zfp = {}
-        elif isinstance(from_zfp, string_or_bytes):
+        elif isinstance(from_zfp, (str, bytes)):
             from_zfp = {namelist[0]: from_zfp}
 
         for name in failed:
diff --git a/src/calibre/db/backend.py b/src/calibre/db/backend.py
index 79c694a619..d13787cf66 100644
--- a/src/calibre/db/backend.py
+++ b/src/calibre/db/backend.py
@@ -72,7 +72,7 @@ from calibre.utils.formatter_functions import compile_user_template_functions, f
 from calibre.utils.icu import lower as icu_lower
 from calibre.utils.icu import sort_key
 from calibre.utils.resources import get_path as P
-from polyglot.builtins import cmp, itervalues, native_string_type, reraise, string_or_bytes
+from polyglot.builtins import cmp, itervalues, native_string_type, reraise
 
 # }}}
 
@@ -1727,7 +1727,7 @@ class DB:
     def copy_cover_to(self, path, dest, windows_atomic_move=None, use_hardlink=False, report_file_size=None):
         path = os.path.abspath(os.path.join(self.library_path, path, COVER_FILE_NAME))
         if windows_atomic_move is not None:
-            if not isinstance(dest, string_or_bytes):
+            if not isinstance(dest, (str, bytes)):
                 raise Exception('Error, you must pass the dest as a path when'
                         ' using windows_atomic_move')
             if os.access(path, os.R_OK) and dest and not samefile(dest, path):
@@ -1837,7 +1837,7 @@ class DB:
         if path is None:
             return False
         if windows_atomic_move is not None:
-            if not isinstance(dest, string_or_bytes):
+            if not isinstance(dest, (str, bytes)):
                 raise Exception('Error, you must pass the dest as a path when'
                         ' using windows_atomic_move')
             if dest:
@@ -2637,7 +2637,7 @@ class DB:
 
     def set_conversion_options(self, options, fmt):
         def map_data(x):
-            if not isinstance(x, string_or_bytes):
+            if not isinstance(x, (str, bytes)):
                 x = native_string_type(x)
             x = x.encode('utf-8') if isinstance(x, str) else x
             x = pickle_binary_string(x)
diff --git a/src/calibre/db/cache.py b/src/calibre/db/cache.py
index 24ccc6e88c..2e44eb07d6 100644
--- a/src/calibre/db/cache.py
+++ b/src/calibre/db/cache.py
@@ -52,7 +52,7 @@ from calibre.utils.filenames import make_long_path_useable
 from calibre.utils.icu import lower as icu_lower
 from calibre.utils.icu import sort_key
 from calibre.utils.localization import canonicalize_lang
-from polyglot.builtins import cmp, iteritems, itervalues, string_or_bytes
+from polyglot.builtins import cmp, iteritems, itervalues
 
 
 class ExtraFile(NamedTuple):
@@ -1651,7 +1651,7 @@ class Cache:
             bimap, simap = {}, {}
             sfield = self.fields[name + '_index']
             for k, v in book_id_to_val_map.items():
-                if isinstance(v, string_or_bytes):
+                if isinstance(v, (str, bytes)):
                     v, sid = get_series_values(v)
                 else:
                     v = sid = None
@@ -1882,7 +1882,7 @@ class Cache:
         # force_changes has no effect on cover manipulation
         try:
             cdata = mi.cover_data[1]
-            if cdata is None and isinstance(mi.cover, string_or_bytes) and mi.cover and os.access(mi.cover, os.R_OK):
+            if cdata is None and isinstance(mi.cover, (str, bytes)) and mi.cover and os.access(mi.cover, os.R_OK):
                 with open(mi.cover, 'rb') as f:
                     cdata = f.read() or None
             if cdata is not None:
diff --git a/src/calibre/db/search.py b/src/calibre/db/search.py
index b5e5186e3f..ae8436ff13 100644
--- a/src/calibre/db/search.py
+++ b/src/calibre/db/search.py
@@ -21,7 +21,7 @@ from calibre.utils.icu import lower as icu_lower
 from calibre.utils.icu import primary_contains, primary_no_punc_contains, sort_key
 from calibre.utils.localization import canonicalize_lang, lang_map
 from calibre.utils.search_query_parser import ParseException, SearchQueryParser
-from polyglot.builtins import iteritems, string_or_bytes
+from polyglot.builtins import iteritems
 
 CONTAINS_MATCH = 0
 EQUALS_MATCH   = 1
@@ -210,7 +210,7 @@ class DateSearch:  # {{{
                     field_count = query.count('/') + 1
 
         for v, book_ids in field_iter():
-            if isinstance(v, string_or_bytes):
+            if isinstance(v, (str, bytes)):
                 v = parse_date(v)
             if v is not None and relop(dt_as_local(v), qd, field_count):
                 matches |= book_ids
@@ -773,7 +773,7 @@ class Parser(SearchQueryParser):  # {{{
             if location in text_fields:
                 for val, book_ids in self.field_iter(location, current_candidates):
                     if val is not None:
-                        if isinstance(val, string_or_bytes):
+                        if isinstance(val, (str, bytes)):
                             val = (val,)
                         if _match(q, val, matchkind, use_primary_find_in_search=upf, case_sensitive=case_sensitive):
                             matches |= book_ids
diff --git a/src/calibre/db/utils.py b/src/calibre/db/utils.py
index 1fb766475b..14a4df164a 100644
--- a/src/calibre/db/utils.py
+++ b/src/calibre/db/utils.py
@@ -18,7 +18,6 @@ from calibre import as_unicode, prints
 from calibre.constants import cache_dir, get_windows_number_formats, iswindows, preferred_encoding
 from calibre.utils.icu import lower as icu_lower
 from calibre.utils.localization import canonicalize_lang, ngettext
-from polyglot.builtins import string_or_bytes
 
 
 def force_to_bool(val):
@@ -48,7 +47,7 @@ def fuzzy_title_patterns():
     if _fuzzy_title_patterns is None:
         from calibre.ebooks.metadata import get_title_sort_pat
         _fuzzy_title_patterns = tuple((re.compile(pat, re.IGNORECASE) if
-            isinstance(pat, string_or_bytes) else pat, repl) for pat, repl in
+            isinstance(pat, (str, bytes)) else pat, repl) for pat, repl in
                 [
                     (r'[\[\](){}<>\'";,:#]', ''),
                     (get_title_sort_pat(), ''),
diff --git a/src/calibre/devices/android/driver.py b/src/calibre/devices/android/driver.py
index 56cdd5536b..afc4f30f88 100644
--- a/src/calibre/devices/android/driver.py
+++ b/src/calibre/devices/android/driver.py
@@ -8,7 +8,6 @@ import os
 from calibre import fsync
 from calibre.devices.usbms.driver import USBMS
 from calibre.utils.resources import get_image_path as I
-from polyglot.builtins import string_or_bytes
 
 HTC_BCDS = [0x100, 0x0222, 0x0224, 0x0226, 0x227, 0x228, 0x229, 0x0231, 0x9999]
 
@@ -286,7 +285,7 @@ class ANDROID(USBMS):
             opts = [self.EBOOK_DIR_MAIN, '']
 
         def strtolist(x):
-            if isinstance(x, string_or_bytes):
+            if isinstance(x, (str, bytes)):
                 x = [y.strip() for y in x.split(',')]
             return x or []
 
diff --git a/src/calibre/devices/kobo/driver.py b/src/calibre/devices/kobo/driver.py
index 6ad5c1cfec..a446a90d50 100644
--- a/src/calibre/devices/kobo/driver.py
+++ b/src/calibre/devices/kobo/driver.py
@@ -4321,7 +4321,7 @@ class KOBOTOUCH(KOBO):
                 debugging_title = settings.extra_customization[OPT_DEBUGGING_TITLE]
                 start_subclass_extra_options = OPT_DEBUGGING_TITLE + 1
 
-            settings.debugging_title = debugging_title if isinstance(debugging_title, string_or_bytes) else ''
+            settings.debugging_title = debugging_title if isinstance(debugging_title, (str, bytes)) else ''
             settings.update_device_metadata = settings.update_series
             settings.extra_customization = settings.extra_customization[start_subclass_extra_options:]
 
diff --git a/src/calibre/devices/usbms/books.py b/src/calibre/devices/usbms/books.py
index a7c65e29fc..69857993e1 100644
--- a/src/calibre/devices/usbms/books.py
+++ b/src/calibre/devices/usbms/books.py
@@ -17,7 +17,7 @@ from calibre.ebooks.metadata.book.base import Metadata
 from calibre.prints import debug_print
 from calibre.utils.config_base import tweaks
 from calibre.utils.icu import sort_key
-from polyglot.builtins import cmp, itervalues, string_or_bytes
+from polyglot.builtins import cmp, itervalues
 
 
 def none_cmp(xx, yy):
@@ -33,7 +33,7 @@ def none_cmp(xx, yy):
         return 1
     if y is None:
         return -1
-    if isinstance(x, string_or_bytes) and isinstance(y, string_or_bytes):
+    if isinstance(x, (str, bytes)) and isinstance(y, (str, bytes)):
         x, y = sort_key(force_unicode(x)), sort_key(force_unicode(y))
     try:
         c = cmp(x, y)
diff --git a/src/calibre/devices/usbms/device.py b/src/calibre/devices/usbms/device.py
index 34be396341..86b419cc18 100644
--- a/src/calibre/devices/usbms/device.py
+++ b/src/calibre/devices/usbms/device.py
@@ -25,7 +25,6 @@ from calibre.devices.errors import DeviceError
 from calibre.devices.interface import FAKE_DEVICE_SERIAL, DevicePlugin, ModelMetadata
 from calibre.devices.usbms.deviceconfig import DeviceConfig
 from calibre.utils.filenames import ascii_filename as sanitize
-from polyglot.builtins import string_or_bytes
 
 if ismacos:
     osx_sanitize_name_pat = re.compile(r'[.-]')
@@ -965,7 +964,7 @@ class Device(DeviceConfig, DevicePlugin):
         sanity_check(on_card, files, self.card_prefix(), self.free_space())
 
         def get_dest_dir(prefix, candidates):
-            if isinstance(candidates, string_or_bytes):
+            if isinstance(candidates, (str, bytes)):
                 candidates = [candidates]
             if not candidates:
                 candidates = ['']
diff --git a/src/calibre/devices/usbms/driver.py b/src/calibre/devices/usbms/driver.py
index c826dd42fc..16ab2f0b26 100644
--- a/src/calibre/devices/usbms/driver.py
+++ b/src/calibre/devices/usbms/driver.py
@@ -20,7 +20,7 @@ from calibre.devices.usbms.cli import CLI
 from calibre.devices.usbms.device import Device
 from calibre.ebooks.metadata.book.json_codec import JsonCodec
 from calibre.prints import debug_print
-from polyglot.builtins import itervalues, string_or_bytes
+from polyglot.builtins import itervalues
 
 
 def safe_walk(top, topdown=True, onerror=None, followlinks=False, maxdepth=128):
@@ -254,7 +254,7 @@ class USBMS(CLI, Device):
                     import traceback
                     traceback.print_exc()
             return changed
-        if isinstance(ebook_dirs, string_or_bytes):
+        if isinstance(ebook_dirs, (str, bytes)):
             ebook_dirs = [ebook_dirs]
         for ebook_dir in ebook_dirs:
             ebook_dir = self.path_to_unicode(ebook_dir)
diff --git a/src/calibre/ebooks/conversion/plumber.py b/src/calibre/ebooks/conversion/plumber.py
index b59d67c0df..ec36c7f569 100644
--- a/src/calibre/ebooks/conversion/plumber.py
+++ b/src/calibre/ebooks/conversion/plumber.py
@@ -27,7 +27,6 @@ from calibre.ebooks.conversion.preprocess import HTMLPreProcessor
 from calibre.ptempfile import PersistentTemporaryDirectory
 from calibre.utils.date import parse_date
 from calibre.utils.zipfile import ZipFile
-from polyglot.builtins import string_or_bytes
 
 DEBUG_README=b'''
 This debug folder contains snapshots of the e-book as it passes through the
@@ -1004,7 +1003,7 @@ OptionRecommendation(name='search_replace',
 
     def dump_input(self, ret, output_dir):
         out_dir = os.path.join(self.opts.debug_pipeline, 'input')
-        if isinstance(ret, string_or_bytes):
+        if isinstance(ret, (str, bytes)):
             shutil.copytree(output_dir, out_dir)
         else:
             if not os.path.exists(out_dir):
@@ -1119,7 +1118,7 @@ OptionRecommendation(name='search_replace',
 
         if self.opts.transform_html_rules:
             transform_html_rules = self.opts.transform_html_rules
-            if isinstance(transform_html_rules, string_or_bytes):
+            if isinstance(transform_html_rules, (str, bytes)):
                 transform_html_rules = json.loads(transform_html_rules)
             from calibre.ebooks.html_transform_rules import transform_conversion_book
             transform_conversion_book(self.oeb, self.opts, transform_html_rules)
@@ -1212,7 +1211,7 @@ OptionRecommendation(name='search_replace',
         transform_css_rules = ()
         if self.opts.transform_css_rules:
             transform_css_rules = self.opts.transform_css_rules
-            if isinstance(transform_css_rules, string_or_bytes):
+            if isinstance(transform_css_rules, (str, bytes)):
                 transform_css_rules = json.loads(transform_css_rules)
         flattener = CSSFlattener(fbase=fbase, fkey=fkey,
                 lineh=line_height,
diff --git a/src/calibre/ebooks/covers.py b/src/calibre/ebooks/covers.py
index 4c6a4a335e..8a6a5d1c15 100644
--- a/src/calibre/ebooks/covers.py
+++ b/src/calibre/ebooks/covers.py
@@ -43,7 +43,7 @@ from calibre.gui2 import config, ensure_app, load_builtin_fonts, pixmap_to_data
 from calibre.utils.cleantext import clean_ascii_chars, clean_xml_chars
 from calibre.utils.config import JSONConfig
 from calibre.utils.resources import get_image_path as I
-from polyglot.builtins import itervalues, string_or_bytes
+from polyglot.builtins import itervalues
 
 # Default settings {{{
 cprefs = JSONConfig('cover_generation')
@@ -289,7 +289,7 @@ def format_fields(mi, prefs):
 
 @contextmanager
 def preserve_fields(obj, fields):
-    if isinstance(fields, string_or_bytes):
+    if isinstance(fields, (str, bytes)):
         fields = fields.split()
     null = object()
     mem = {f:getattr(obj, f, null) for f in fields}
diff --git a/src/calibre/ebooks/fb2/fb2ml.py b/src/calibre/ebooks/fb2/fb2ml.py
index a7efbaabb2..092dbfc9bd 100644
--- a/src/calibre/ebooks/fb2/fb2ml.py
+++ b/src/calibre/ebooks/fb2/fb2ml.py
@@ -20,7 +20,6 @@ from calibre.utils.img import save_cover_data_to
 from calibre.utils.localization import lang_as_iso639_1
 from calibre.utils.xml_parse import safe_xml_fromstring
 from polyglot.binary import as_base64_unicode
-from polyglot.builtins import string_or_bytes
 from polyglot.urllib import urlparse
 
 
@@ -408,9 +407,9 @@ class FB2MLizer:
         elem = elem_tree
 
         # Ensure what we are converting is not a string and that the fist tag is part of the XHTML namespace.
-        if not isinstance(elem_tree.tag, string_or_bytes) or namespace(elem_tree.tag) != XHTML_NS:
+        if not isinstance(elem_tree.tag, (str, bytes)) or namespace(elem_tree.tag) != XHTML_NS:
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) == XHTML_NS \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) == XHTML_NS \
                     and elem.tail:
                 return [elem.tail]
             return []
diff --git a/src/calibre/ebooks/htmlz/oeb2html.py b/src/calibre/ebooks/htmlz/oeb2html.py
index 5d4ccb4b90..07da373720 100644
--- a/src/calibre/ebooks/htmlz/oeb2html.py
+++ b/src/calibre/ebooks/htmlz/oeb2html.py
@@ -17,7 +17,7 @@ from calibre import prepare_string_for_xml
 from calibre.ebooks.oeb.base import OEB_IMAGES, SVG_NS, XHTML, XHTML_NS, XLINK, barename, namespace, rewrite_links, urlnormalize
 from calibre.ebooks.oeb.stylizer import Stylizer
 from calibre.utils.logging import default_log
-from polyglot.builtins import as_unicode, string_or_bytes
+from polyglot.builtins import as_unicode
 from polyglot.urllib import urldefrag
 
 SELF_CLOSING_TAGS = {'area', 'base', 'basefont', 'br', 'hr', 'input', 'img', 'link', 'meta'}
@@ -104,7 +104,7 @@ class OEB2HTML:
             for el in root.iter():
                 attribs = el.attrib
                 try:
-                    if not isinstance(el.tag, string_or_bytes):
+                    if not isinstance(el.tag, (str, bytes)):
                         continue
                 except Exception:
                     continue
@@ -168,10 +168,10 @@ class OEB2HTMLNoCSSizer(OEB2HTML):
         '''
 
         # We can only processes tags. If there isn't a tag return any text.
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
            or namespace(elem.tag) not in (XHTML_NS, SVG_NS):
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) in (XHTML_NS, SVG_NS) \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) in (XHTML_NS, SVG_NS) \
                     and elem.tail:
                 return [elem.tail]
             return ['']
@@ -258,10 +258,10 @@ class OEB2HTMLInlineCSSizer(OEB2HTML):
         '''
 
         # We can only processes tags. If there isn't a tag return any text.
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
            or namespace(elem.tag) not in (XHTML_NS, SVG_NS):
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) in (XHTML_NS, SVG_NS) \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) in (XHTML_NS, SVG_NS) \
                     and elem.tail:
                 return [elem.tail]
             return ['']
@@ -362,10 +362,10 @@ class OEB2HTMLClassCSSizer(OEB2HTML):
         '''
 
         # We can only processes tags. If there isn't a tag return any text.
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
            or namespace(elem.tag) not in (XHTML_NS, SVG_NS):
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) in (XHTML_NS, SVG_NS) \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) in (XHTML_NS, SVG_NS) \
                     and elem.tail:
                 return [elem.tail]
             return ['']
diff --git a/src/calibre/ebooks/lit/reader.py b/src/calibre/ebooks/lit/reader.py
index 60fad6712c..2ed4a1da55 100644
--- a/src/calibre/ebooks/lit/reader.py
+++ b/src/calibre/ebooks/lit/reader.py
@@ -20,7 +20,7 @@ from calibre.ebooks.lit.maps import HTML_MAP, OPF_MAP
 from calibre.ebooks.oeb.base import urlnormalize, xpath
 from calibre.ebooks.oeb.reader import OEBReader
 from calibre_extensions import lzx, msdes
-from polyglot.builtins import itervalues, string_or_bytes
+from polyglot.builtins import itervalues
 from polyglot.urllib import unquote as urlunquote
 from polyglot.urllib import urldefrag
 
@@ -286,7 +286,7 @@ class UnBinary:
                         attr = current_map[oc]
                     elif oc in self.attr_map:
                         attr = self.attr_map[oc]
-                    if not attr or not isinstance(attr, string_or_bytes):
+                    if not attr or not isinstance(attr, (str, bytes)):
                         raise LitError(
                             f'Unknown attribute {oc} in tag {tag_name}')
                     if attr.startswith('%'):
diff --git a/src/calibre/ebooks/lit/writer.py b/src/calibre/ebooks/lit/writer.py
index d5973c392a..654f1d8be1 100644
--- a/src/calibre/ebooks/lit/writer.py
+++ b/src/calibre/ebooks/lit/writer.py
@@ -26,7 +26,7 @@ from calibre.ebooks.lit.reader import DirectoryEntry
 from calibre.ebooks.oeb.base import CSS_MIME, OEB_DOCS, OEB_STYLES, OPF_MIME, XHTML_MIME, XML, XML_NS, prefixname, urlnormalize
 from calibre.ebooks.oeb.stylizer import Stylizer
 from calibre_extensions import msdes
-from polyglot.builtins import native_string_type, string_or_bytes
+from polyglot.builtins import native_string_type
 from polyglot.urllib import unquote, urldefrag
 
 __all__ = ['LitWriter']
@@ -173,7 +173,7 @@ class ReBinary:
 
     def tree_to_binary(self, elem, nsrmap=NSRMAP, parents=[],
                        inhead=False, preserve=False):
-        if not isinstance(elem.tag, string_or_bytes):
+        if not isinstance(elem.tag, (str, bytes)):
             # Don't emit any comments or raw entities
             return
         nsrmap = copy.copy(nsrmap)
diff --git a/src/calibre/ebooks/lrf/html/table.py b/src/calibre/ebooks/lrf/html/table.py
index 137f76ddc4..8cf1498340 100644
--- a/src/calibre/ebooks/lrf/html/table.py
+++ b/src/calibre/ebooks/lrf/html/table.py
@@ -7,7 +7,7 @@ import sys
 
 from calibre.ebooks.lrf.fonts import get_font
 from calibre.ebooks.lrf.pylrs.pylrs import CR, CharButton, LrsTextTag, Paragraph, Plot, Span, Text, TextBlock
-from polyglot.builtins import native_string_type, string_or_bytes
+from polyglot.builtins import native_string_type
 
 
 def ceil(num):
@@ -39,7 +39,7 @@ def tokens(tb):
             yield 2, None
         elif isinstance(x, Text):
             yield x.text, cattrs(attrs, {})
-        elif isinstance(x, string_or_bytes):
+        elif isinstance(x, (str, bytes)):
             yield x, cattrs(attrs, {})
         elif isinstance(x, (CharButton, LrsTextTag)):
             if x.contents:
diff --git a/src/calibre/ebooks/lrf/lrs/convert_from.py b/src/calibre/ebooks/lrf/lrs/convert_from.py
index 821a60f32a..a286afe507 100644
--- a/src/calibre/ebooks/lrf/lrs/convert_from.py
+++ b/src/calibre/ebooks/lrf/lrs/convert_from.py
@@ -42,7 +42,6 @@ from calibre.ebooks.lrf.pylrs.pylrs import (
     TextStyle,
 )
 from calibre.utils.config import OptionParser
-from polyglot.builtins import string_or_bytes
 
 
 class LrsParser:
@@ -113,7 +112,7 @@ class LrsParser:
             if isinstance(contents[0], NavigableString):
                 contents[0] = contents[0].string.lstrip()
             for item in contents:
-                if isinstance(item, string_or_bytes):
+                if isinstance(item, (str, bytes)):
                     p.append(item)
                 elif isinstance(item, NavigableString):
                     p.append(item.string)
diff --git a/src/calibre/ebooks/lrf/meta.py b/src/calibre/ebooks/lrf/meta.py
index 76dd552e5b..18cb32be80 100644
--- a/src/calibre/ebooks/lrf/meta.py
+++ b/src/calibre/ebooks/lrf/meta.py
@@ -24,7 +24,6 @@ from shutil import copyfileobj
 from calibre.ebooks.chardet import xml_to_unicode
 from calibre.ebooks.metadata import MetaInformation, string_to_authors
 from calibre.utils.cleantext import clean_xml_chars
-from polyglot.builtins import string_or_bytes
 
 BYTE      = '<B'  #: Unsigned char little endian encoded in 1 byte
 WORD      = '<H'  #: Unsigned short little endian encoded in 2 bytes
@@ -98,7 +97,7 @@ class fixed_stringfield:
         return obj.unpack(start=self._start, fmt='<'+length+'s')[0]
 
     def __set__(self, obj, val):
-        if not isinstance(val, string_or_bytes):
+        if not isinstance(val, (str, bytes)):
             val = str(val)
         if isinstance(val, str):
             val = val.encode('utf-8')
diff --git a/src/calibre/ebooks/lrf/pylrs/elements.py b/src/calibre/ebooks/lrf/pylrs/elements.py
index 0087ad9704..273a495f8b 100644
--- a/src/calibre/ebooks/lrf/pylrs/elements.py
+++ b/src/calibre/ebooks/lrf/pylrs/elements.py
@@ -1,7 +1,5 @@
 ''' elements.py -- replacements and helpers for ElementTree '''
 
-from polyglot.builtins import string_or_bytes
-
 
 class ElementWriter:
 
@@ -24,7 +22,7 @@ class ElementWriter:
 
     def _writeAttribute(self, f, name, value):
         f.write(f' {name!s}="')
-        if not isinstance(value, string_or_bytes):
+        if not isinstance(value, (str, bytes)):
             value = str(value)
         value = self._encodeCdata(value)
         value = value.replace('"', '&quot;')
diff --git a/src/calibre/ebooks/lrf/pylrs/pylrf.py b/src/calibre/ebooks/lrf/pylrs/pylrf.py
index fbb266870a..797fff6a92 100644
--- a/src/calibre/ebooks/lrf/pylrs/pylrf.py
+++ b/src/calibre/ebooks/lrf/pylrs/pylrf.py
@@ -11,8 +11,6 @@ import os
 import struct
 import zlib
 
-from polyglot.builtins import string_or_bytes
-
 from .pylrfopt import tagListOptimizer
 
 PYLRF_VERSION = '1.0'
@@ -400,7 +398,7 @@ class LrfTag:
         for f in self.format:
             if isinstance(f, dict):
                 p = f[p]
-            elif isinstance(f, string_or_bytes):
+            elif isinstance(f, (str, bytes)):
                 if isinstance(p, tuple):
                     writeString(lrf, struct.pack(f, *p))
                 else:
diff --git a/src/calibre/ebooks/lrf/pylrs/pylrs.py b/src/calibre/ebooks/lrf/pylrs/pylrs.py
index cbbfd2cdbe..1b358b8636 100644
--- a/src/calibre/ebooks/lrf/pylrs/pylrs.py
+++ b/src/calibre/ebooks/lrf/pylrs/pylrs.py
@@ -66,7 +66,7 @@ DEFAULT_SOURCE_ENCODING = 'cp1252'      # default is us-windows character set
 DEFAULT_GENREADING      = 'fs'          # default is yes to both lrf and lrs
 
 from calibre import __appname__, __version__, replace_entities
-from polyglot.builtins import iteritems, native_string_type, string_or_bytes
+from polyglot.builtins import iteritems, native_string_type
 
 
 class LrsError(Exception):
@@ -105,7 +105,7 @@ def ElementWithReading(tag, text, reading=False):
 
     if text is None:
         readingText = ''
-    elif isinstance(text, string_or_bytes):
+    elif isinstance(text, (str, bytes)):
         readingText = text
     else:
         # assumed to be a sequence of (name, sortas)
@@ -161,7 +161,7 @@ class Delegator:
                 setattr(self, m, getattr(d, m))
 
             # for setting in d.getSettings():
-            #     if isinstance(setting, string_or_bytes):
+            #     if isinstance(setting, (str, bytes)):
             #         setting = (d, setting)
             #     delegates = \
             #             self.delegatedSettingsDict.setdefault(setting[1], [])
@@ -292,7 +292,7 @@ class LrsContainer:
         else:
             raise LrsError(f"can't append {content.__class__.__name__} to {self.__class__.__name__}")
 
-        if convertText and isinstance(content, string_or_bytes):
+        if convertText and isinstance(content, (str, bytes)):
             content = Text(content)
 
         content.setParent(self)
@@ -585,14 +585,14 @@ class Book(Delegator):
             ts.attrs['baselineskip'] = rescale(ts.attrs['baselineskip'])
 
     def renderLrs(self, lrsFile, encoding='UTF-8'):
-        if isinstance(lrsFile, string_or_bytes):
+        if isinstance(lrsFile, (str, bytes)):
             lrsFile = codecs.open(lrsFile, 'wb', encoding=encoding)
         self.render(lrsFile, outputEncodingName=encoding)
         lrsFile.close()
 
     def renderLrf(self, lrfFile):
         self.appendReferencedObjects(self)
-        if isinstance(lrfFile, string_or_bytes):
+        if isinstance(lrfFile, (str, bytes)):
             lrfFile = open(lrfFile, 'wb')
         lrfWriter = LrfWriter(self.sourceencoding)
 
@@ -1489,7 +1489,7 @@ class Paragraph(LrsContainer):
         LrsContainer.__init__(self, [Text, CR, DropCaps, CharButton,
                                      LrsSimpleChar1, bytes, str])
         if text is not None:
-            if isinstance(text, string_or_bytes):
+            if isinstance(text, (str, bytes)):
                 text = Text(text)
             self.append(text)
 
@@ -1808,7 +1808,7 @@ class Span(LrsSimpleChar1, LrsContainer):
     def __init__(self, text=None, **attrs):
         LrsContainer.__init__(self, [LrsSimpleChar1, Text, bytes, str])
         if text is not None:
-            if isinstance(text, string_or_bytes):
+            if isinstance(text, (str, bytes)):
                 text = Text(text)
             self.append(text)
 
diff --git a/src/calibre/ebooks/metadata/book/base.py b/src/calibre/ebooks/metadata/book/base.py
index 3d9b93157f..4ae41f4906 100644
--- a/src/calibre/ebooks/metadata/book/base.py
+++ b/src/calibre/ebooks/metadata/book/base.py
@@ -16,7 +16,7 @@ from calibre.library.field_metadata import FieldMetadata
 from calibre.utils.icu import lower as icu_lower
 from calibre.utils.icu import sort_key
 from calibre.utils.localization import ngettext
-from polyglot.builtins import iteritems, string_or_bytes
+from polyglot.builtins import iteritems
 
 # Special sets used to optimize the performance of getting and setting
 # attributes on Metadata objects
@@ -588,7 +588,7 @@ class Metadata:
                     meta = other.get_user_metadata(x, make_copy=True)
                     if meta is not None:
                         self_tags = self.get(x, [])
-                        if isinstance(self_tags, string_or_bytes):
+                        if isinstance(self_tags, (str, bytes)):
                             self_tags = []
                         self.set_user_metadata(x, meta)  # get... did the deepcopy
                         other_tags = other.get(x, [])
diff --git a/src/calibre/ebooks/metadata/rtf.py b/src/calibre/ebooks/metadata/rtf.py
index a1af442fcd..3687ae3288 100644
--- a/src/calibre/ebooks/metadata/rtf.py
+++ b/src/calibre/ebooks/metadata/rtf.py
@@ -10,7 +10,7 @@ import re
 
 from calibre import force_unicode
 from calibre.ebooks.metadata import MetaInformation
-from polyglot.builtins import int_to_byte, string_or_bytes
+from polyglot.builtins import int_to_byte
 
 title_pat    = re.compile(br'\{\\info.*?\{\\title(.*?)(?<!\\)\}', re.DOTALL)
 author_pat   = re.compile(br'\{\\info.*?\{\\author(.*?)(?<!\\)\}', re.DOTALL)
@@ -159,7 +159,7 @@ def create_metadata(stream, options):
         md.append(rf'{{\title {title}}}')
     if options.authors:
         au = options.authors
-        if not isinstance(au, string_or_bytes):
+        if not isinstance(au, (str, bytes)):
             au = ', '.join(au)
         author = encode(au)
         md.append(rf'{{\author {author}}}')
diff --git a/src/calibre/ebooks/metadata/xmp.py b/src/calibre/ebooks/metadata/xmp.py
index 73ddd5e563..66eef6b772 100644
--- a/src/calibre/ebooks/metadata/xmp.py
+++ b/src/calibre/ebooks/metadata/xmp.py
@@ -21,7 +21,7 @@ from calibre.ebooks.metadata.opf2 import dump_dict
 from calibre.utils.date import isoformat, now, parse_date
 from calibre.utils.localization import canonicalize_lang, lang_as_iso639_1
 from calibre.utils.xml_parse import safe_xml_fromstring
-from polyglot.builtins import iteritems, string_or_bytes
+from polyglot.builtins import iteritems
 
 _xml_declaration = re.compile(r'<\?xml[^<>]+encoding\s*=\s*[\'"](.*?)[\'"][^<>]*>', re.IGNORECASE)
 
@@ -489,7 +489,7 @@ def metadata_to_xmp_packet(mi):
         'authors':('dc:creator', True), 'tags':('dc:subject', False), 'publisher':('dc:publisher', False),
     }):
         val = mi.get(prop) or ()
-        if isinstance(val, string_or_bytes):
+        if isinstance(val, (str, bytes)):
             val = [val]
         create_sequence_property(dc, tag, val, ordered)
     if not mi.is_null('pubdate'):
diff --git a/src/calibre/ebooks/mobi/mobiml.py b/src/calibre/ebooks/mobi/mobiml.py
index 066d2125b9..c808153cb5 100644
--- a/src/calibre/ebooks/mobi/mobiml.py
+++ b/src/calibre/ebooks/mobi/mobiml.py
@@ -17,7 +17,6 @@ from calibre.ebooks.oeb.base import XHTML, XHTML_NS, barename, namespace, urlnor
 from calibre.ebooks.oeb.stylizer import Stylizer
 from calibre.ebooks.oeb.transforms.flatcss import KeyMapper
 from calibre.utils.imghdr import identify
-from polyglot.builtins import string_or_bytes
 
 MBP_NS = 'http://mobipocket.com/ns/mbp'
 
@@ -156,7 +155,7 @@ class MobiMLizer:
         return self.fnums[self.fmap[ptsize]]
 
     def mobimlize_measure(self, ptsize):
-        if isinstance(ptsize, string_or_bytes):
+        if isinstance(ptsize, (str, bytes)):
             return ptsize
         embase = self.profile.fbase
         if round(ptsize) < embase:
@@ -199,7 +198,7 @@ class MobiMLizer:
             parent = bstate.nested[-1] if bstate.nested else bstate.body
             indent = istate.indent
             left = istate.left
-            if isinstance(indent, string_or_bytes):
+            if isinstance(indent, (str, bytes)):
                 indent = 0
             if indent < 0 and abs(indent) < left:
                 left += indent
@@ -320,7 +319,7 @@ class MobiMLizer:
         inline = bstate.inline
         content = self.preize_text(text, pre_wrap=istate.pre_wrap) if istate.preserve or istate.pre_wrap else [text]
         for item in content:
-            if isinstance(item, string_or_bytes):
+            if isinstance(item, (str, bytes)):
                 if len(inline) == 0:
                     inline.text = (inline.text or '') + item
                 else:
@@ -331,7 +330,7 @@ class MobiMLizer:
 
     def mobimlize_elem(self, elem, stylizer, bstate, istates,
             ignore_valign=False):
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
            or namespace(elem.tag) != XHTML_NS:
             return
         style = stylizer.style(elem)
diff --git a/src/calibre/ebooks/mobi/writer2/serializer.py b/src/calibre/ebooks/mobi/writer2/serializer.py
index a7137a2730..b9f0bf27a5 100644
--- a/src/calibre/ebooks/mobi/writer2/serializer.py
+++ b/src/calibre/ebooks/mobi/writer2/serializer.py
@@ -14,7 +14,6 @@ from io import BytesIO
 from calibre.ebooks.mobi.mobiml import MBP_NS
 from calibre.ebooks.mobi.utils import is_guide_ref_start
 from calibre.ebooks.oeb.base import OEB_DOCS, XHTML, XHTML_NS, XML_NS, namespace, prefixname, urlnormalize
-from polyglot.builtins import string_or_bytes
 from polyglot.urllib import urldefrag
 
 
@@ -307,7 +306,7 @@ class Serializer:
 
     def serialize_elem(self, elem, item, nsrmap=NSRMAP):
         buf = self.buf
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
             or namespace(elem.tag) not in nsrmap:
             return
         tag = prefixname(elem.tag, nsrmap)
diff --git a/src/calibre/ebooks/odt/input.py b/src/calibre/ebooks/odt/input.py
index b4323e9f5e..c4ff539007 100644
--- a/src/calibre/ebooks/odt/input.py
+++ b/src/calibre/ebooks/odt/input.py
@@ -20,7 +20,7 @@ from odf.opendocument import load as odLoad
 from calibre import CurrentDir, walk
 from calibre.ebooks.oeb.base import _css_logger
 from calibre.utils.xml_parse import safe_xml_fromstring
-from polyglot.builtins import as_bytes, string_or_bytes
+from polyglot.builtins import as_bytes
 
 
 class Extract(ODF2XHTML):
@@ -250,7 +250,7 @@ class Extract(ODF2XHTML):
         # first load the odf structure
         self.lines = []
         self._wfunc = self._wlines
-        if isinstance(odffile, string_or_bytes) \
+        if isinstance(odffile, (str, bytes)) \
                 or hasattr(odffile, 'read'):  # Added by Kovid
             self.document = odLoad(odffile)
         else:
diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py
index 1b934da0ac..684f93c624 100644
--- a/src/calibre/ebooks/oeb/base.py
+++ b/src/calibre/ebooks/oeb/base.py
@@ -30,7 +30,7 @@ from calibre.utils.icu import title_case as icu_title
 from calibre.utils.localization import __, is_rtl_lang
 from calibre.utils.short_uuid import uuid4
 from calibre.utils.xml_parse import safe_xml_fromstring
-from polyglot.builtins import iteritems, itervalues, string_or_bytes
+from polyglot.builtins import iteritems, itervalues
 from polyglot.urllib import unquote as urlunquote
 from polyglot.urllib import urldefrag, urljoin, urlparse, urlunparse
 
@@ -1051,7 +1051,7 @@ class Manifest:
                 mt = self.media_type.lower()
             except Exception:
                 mt = 'application/octet-stream'
-            if not isinstance(data, string_or_bytes):
+            if not isinstance(data, (str, bytes)):
                 pass  # already parsed
             elif mt in OEB_DOCS:
                 data = self._parse_xhtml(data)
@@ -1306,7 +1306,7 @@ class Spine:
         self.page_progression_direction = None
 
     def _linear(self, linear):
-        if isinstance(linear, string_or_bytes):
+        if isinstance(linear, (str, bytes)):
             linear = linear.lower()
         if linear is None or linear in ('yes', 'true'):
             linear = True
diff --git a/src/calibre/ebooks/oeb/parse_utils.py b/src/calibre/ebooks/oeb/parse_utils.py
index a9a1bd932b..af2f06d954 100644
--- a/src/calibre/ebooks/oeb/parse_utils.py
+++ b/src/calibre/ebooks/oeb/parse_utils.py
@@ -13,7 +13,7 @@ from calibre import force_unicode, xml_replace_entities
 from calibre.constants import filesystem_encoding
 from calibre.ebooks.chardet import strip_encoding_declarations, xml_to_unicode
 from calibre.utils.xml_parse import safe_html_fromstring, safe_xml_fromstring
-from polyglot.builtins import iteritems, itervalues, string_or_bytes
+from polyglot.builtins import iteritems, itervalues
 
 XHTML_NS     = 'http://www.w3.org/1999/xhtml'
 XMLNS_NS     = 'http://www.w3.org/2000/xmlns/'
@@ -101,7 +101,7 @@ def html5_parse(data, max_nesting_depth=100):
     # Check that the asinine HTML 5 algorithm did not result in a tree with
     # insane nesting depths
     for x in data.iterdescendants():
-        if isinstance(x.tag, string_or_bytes) and not len(x):  # Leaf node
+        if isinstance(x.tag, (str, bytes)) and not len(x):  # Leaf node
             depth = node_depth(x)
             if depth > max_nesting_depth:
                 raise ValueError(f'HTML 5 parsing resulted in a tree with nesting depth > {max_nesting_depth}')
@@ -297,7 +297,7 @@ def parse_html(data, log=None, decoder=None, preprocessor=None,
         nroot = etree.Element(XHTML('html'),
             nsmap={None: XHTML_NS}, attrib=attrib)
         for elem in data.iterdescendants():
-            if isinstance(elem.tag, string_or_bytes) and \
+            if isinstance(elem.tag, (str, bytes)) and \
                 namespace(elem.tag) == ns:
                 elem.tag = XHTML(barename(elem.tag))
         for elem in data:
diff --git a/src/calibre/ebooks/oeb/polish/embed.py b/src/calibre/ebooks/oeb/polish/embed.py
index 6206446c90..8ba0c8d08e 100644
--- a/src/calibre/ebooks/oeb/polish/embed.py
+++ b/src/calibre/ebooks/oeb/polish/embed.py
@@ -13,14 +13,14 @@ from calibre import prints
 from calibre.ebooks.oeb.base import XHTML
 from calibre.utils.filenames import ascii_filename
 from calibre.utils.icu import lower as icu_lower
-from polyglot.builtins import itervalues, string_or_bytes
+from polyglot.builtins import itervalues
 
 props = {'font-family':None, 'font-weight':'normal', 'font-style':'normal', 'font-stretch':'normal'}
 
 
 def matching_rule(font, rules):
     ff = font['font-family']
-    if not isinstance(ff, string_or_bytes):
+    if not isinstance(ff, (str, bytes)):
         ff = tuple(ff)[0]
     family = icu_lower(ff)
     wt = font['font-weight']
@@ -30,7 +30,7 @@ def matching_rule(font, rules):
     for rule in rules:
         if rule['font-style'] == style and rule['font-stretch'] == stretch and rule['font-weight'] == wt:
             ff = rule['font-family']
-            if not isinstance(ff, string_or_bytes):
+            if not isinstance(ff, (str, bytes)):
                 ff = tuple(ff)[0]
             if icu_lower(ff) == family:
                 return rule
@@ -161,7 +161,7 @@ def do_embed(container, font, report):
 def embed_font(container, font, all_font_rules, report, warned):
     rule = matching_rule(font, all_font_rules)
     ff = font['font-family']
-    if not isinstance(ff, string_or_bytes):
+    if not isinstance(ff, (str, bytes)):
         ff = ff[0]
     if rule is None:
         from calibre.utils.fonts.scanner import NoFonts, font_scanner
diff --git a/src/calibre/ebooks/oeb/polish/split.py b/src/calibre/ebooks/oeb/polish/split.py
index 0908c456e9..d084131cda 100644
--- a/src/calibre/ebooks/oeb/polish/split.py
+++ b/src/calibre/ebooks/oeb/polish/split.py
@@ -12,7 +12,6 @@ from calibre.ebooks.oeb.base import OEB_DOCS, OPF, XHTML, XPNSMAP, XPath, barena
 from calibre.ebooks.oeb.polish.errors import MalformedMarkup
 from calibre.ebooks.oeb.polish.replace import LinkRebaser
 from calibre.ebooks.oeb.polish.toc import node_from_loc
-from polyglot.builtins import string_or_bytes
 from polyglot.urllib import urlparse
 
 
@@ -396,9 +395,9 @@ def merge_html(container, names, master, insert_page_breaks=False):
 
         first_child = ''
         for first_child in children:
-            if not isinstance(first_child, string_or_bytes):
+            if not isinstance(first_child, (str, bytes)):
                 break
-        if isinstance(first_child, string_or_bytes):
+        if isinstance(first_child, (str, bytes)):
             # body contained only text, no tags
             first_child = body.makeelement(XHTML('p'))
             first_child.text, children[0] = children[0], first_child
@@ -434,7 +433,7 @@ def merge_html(container, names, master, insert_page_breaks=False):
                 a.set('href', '#' + amap[q])
 
         for child in children:
-            if isinstance(child, string_or_bytes):
+            if isinstance(child, (str, bytes)):
                 add_text(master_body, child)
             else:
                 master_body.append(copy.deepcopy(child))
diff --git a/src/calibre/ebooks/oeb/transforms/flatcss.py b/src/calibre/ebooks/oeb/transforms/flatcss.py
index f3899a940f..614b7af9b5 100644
--- a/src/calibre/ebooks/oeb/transforms/flatcss.py
+++ b/src/calibre/ebooks/oeb/transforms/flatcss.py
@@ -23,7 +23,7 @@ from calibre.ebooks.oeb.base import CSS_MIME, OEB_STYLES, SVG, SVG_NS, XHTML, XH
 from calibre.ebooks.oeb.stylizer import Stylizer
 from calibre.utils.filenames import ascii_filename, ascii_text
 from calibre.utils.icu import numeric_sort_key
-from polyglot.builtins import iteritems, string_or_bytes
+from polyglot.builtins import iteritems
 
 COLLAPSE = re.compile(r'[ \t\r\n\v]+')
 STRIPNUM = re.compile(r'[-0-9]+$')
@@ -361,7 +361,7 @@ class CSSFlattener:
                     cssdict[property] = f'{value/fsize:0.5f}em'
 
     def flatten_node(self, node, stylizer, names, styles, pseudo_styles, psize, item_id, recurse=True):
-        if not isinstance(node.tag, string_or_bytes) or namespace(node.tag) not in (XHTML_NS, SVG_NS):
+        if not isinstance(node.tag, (str, bytes)) or namespace(node.tag) not in (XHTML_NS, SVG_NS):
             return
         tag = barename(node.tag)
         style = stylizer.style(node)
diff --git a/src/calibre/ebooks/oeb/transforms/manglecase.py b/src/calibre/ebooks/oeb/transforms/manglecase.py
index aebd76a930..a60c0e734a 100644
--- a/src/calibre/ebooks/oeb/transforms/manglecase.py
+++ b/src/calibre/ebooks/oeb/transforms/manglecase.py
@@ -12,7 +12,6 @@ from calibre.ebooks.oeb.stylizer import Stylizer
 from calibre.utils.icu import lower as icu_lower
 from calibre.utils.icu import title_case as icu_title
 from calibre.utils.icu import upper as icu_upper
-from polyglot.builtins import string_or_bytes
 
 CASE_MANGLER_CSS = '''
 .calibre_lowercase {
@@ -97,7 +96,7 @@ class CaseMangler:
                 last = child
 
     def mangle_elem(self, elem, stylizer):
-        if not isinstance(elem.tag, string_or_bytes) or \
+        if not isinstance(elem.tag, (str, bytes)) or \
            namespace(elem.tag) != XHTML_NS:
             return
         children = list(elem)
diff --git a/src/calibre/ebooks/pml/pmlml.py b/src/calibre/ebooks/pml/pmlml.py
index 6fca069843..351c5405b8 100644
--- a/src/calibre/ebooks/pml/pmlml.py
+++ b/src/calibre/ebooks/pml/pmlml.py
@@ -13,7 +13,6 @@ from lxml import etree
 from calibre.ebooks.pdb.ereader import image_name
 from calibre.ebooks.pml import unipmlcode
 from calibre.utils.xml_parse import safe_xml_fromstring
-from polyglot.builtins import string_or_bytes
 
 TAG_MAP = {
     'b'       : 'B',
@@ -223,9 +222,9 @@ class PMLMLizer:
     def dump_text(self, elem, stylizer, page, tag_stack=[]):
         from calibre.ebooks.oeb.base import XHTML_NS, barename, namespace
 
-        if not isinstance(elem.tag, string_or_bytes) or namespace(elem.tag) != XHTML_NS:
+        if not isinstance(elem.tag, (str, bytes)) or namespace(elem.tag) != XHTML_NS:
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) == XHTML_NS \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) == XHTML_NS \
                     and elem.tail:
                 return [elem.tail]
             return []
diff --git a/src/calibre/ebooks/rb/rbml.py b/src/calibre/ebooks/rb/rbml.py
index 57e63d9fa2..1d679fd3f7 100644
--- a/src/calibre/ebooks/rb/rbml.py
+++ b/src/calibre/ebooks/rb/rbml.py
@@ -10,7 +10,6 @@ import re
 
 from calibre import prepare_string_for_xml
 from calibre.ebooks.rb import unique_name
-from polyglot.builtins import string_or_bytes
 
 TAGS = [
     'b',
@@ -141,9 +140,9 @@ class RBMLizer:
     def dump_text(self, elem, stylizer, page, tag_stack=[]):
         from calibre.ebooks.oeb.base import XHTML_NS, barename, namespace
 
-        if not isinstance(elem.tag, string_or_bytes) or namespace(elem.tag) != XHTML_NS:
+        if not isinstance(elem.tag, (str, bytes)) or namespace(elem.tag) != XHTML_NS:
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) == XHTML_NS \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) == XHTML_NS \
                     and elem.tail:
                 return [elem.tail]
             return ['']
diff --git a/src/calibre/ebooks/rtf/rtfml.py b/src/calibre/ebooks/rtf/rtfml.py
index 6e28b2bfdc..f35eb9d201 100644
--- a/src/calibre/ebooks/rtf/rtfml.py
+++ b/src/calibre/ebooks/rtf/rtfml.py
@@ -16,7 +16,6 @@ from lxml import etree
 from calibre.ebooks.metadata import authors_to_string
 from calibre.utils.img import save_cover_data_to
 from calibre.utils.imghdr import identify
-from polyglot.builtins import string_or_bytes
 
 TAGS = {
     'b': '\\b',
@@ -213,10 +212,10 @@ class RTFMLizer:
     def dump_text(self, elem, stylizer, tag_stack=[]):
         from calibre.ebooks.oeb.base import XHTML_NS, barename, namespace, urlnormalize
 
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
            or namespace(elem.tag) != XHTML_NS:
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) == XHTML_NS \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) == XHTML_NS \
                     and elem.tail:
                 return elem.tail
             return ''
diff --git a/src/calibre/ebooks/snb/snbml.py b/src/calibre/ebooks/snb/snbml.py
index 5dc9940da5..49080003be 100644
--- a/src/calibre/ebooks/snb/snbml.py
+++ b/src/calibre/ebooks/snb/snbml.py
@@ -11,8 +11,6 @@ import re
 
 from lxml import etree
 
-from polyglot.builtins import string_or_bytes
-
 
 def ProcessFileName(fileName):
     # Flat the path
@@ -211,10 +209,10 @@ class SNBMLizer:
     def dump_text(self, subitems, elem, stylizer, end='', pre=False, li=''):
         from calibre.ebooks.oeb.base import XHTML_NS, barename, namespace
 
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
            or namespace(elem.tag) != XHTML_NS:
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) == XHTML_NS \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) == XHTML_NS \
                     and elem.tail:
                 return [elem.tail]
             return ['']
diff --git a/src/calibre/ebooks/txt/markdownml.py b/src/calibre/ebooks/txt/markdownml.py
index c710f8bda4..5dee399061 100644
--- a/src/calibre/ebooks/txt/markdownml.py
+++ b/src/calibre/ebooks/txt/markdownml.py
@@ -12,7 +12,6 @@ from functools import partial
 from calibre.ebooks.htmlz.oeb2html import OEB2HTML
 from calibre.ebooks.oeb.base import XHTML, XHTML_NS, barename, namespace, rewrite_links
 from calibre.ebooks.oeb.stylizer import Stylizer
-from polyglot.builtins import string_or_bytes
 
 
 class MarkdownMLizer(OEB2HTML):
@@ -108,10 +107,10 @@ class MarkdownMLizer(OEB2HTML):
         '''
 
         # We can only processes tags. If there isn't a tag return any text.
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
            or namespace(elem.tag) != XHTML_NS:
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) == XHTML_NS \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) == XHTML_NS \
                     and elem.tail:
                 return [elem.tail]
             return ['']
diff --git a/src/calibre/ebooks/txt/textileml.py b/src/calibre/ebooks/txt/textileml.py
index 355c2c2df6..25bf9e3f34 100644
--- a/src/calibre/ebooks/txt/textileml.py
+++ b/src/calibre/ebooks/txt/textileml.py
@@ -13,7 +13,6 @@ from calibre.ebooks.htmlz.oeb2html import OEB2HTML
 from calibre.ebooks.oeb.base import XHTML, XHTML_NS, barename, namespace, rewrite_links
 from calibre.ebooks.oeb.stylizer import Stylizer
 from calibre.ebooks.textile.unsmarten import unsmarten
-from polyglot.builtins import string_or_bytes
 
 
 class TextileMLizer(OEB2HTML):
@@ -231,10 +230,10 @@ class TextileMLizer(OEB2HTML):
         '''
 
         # We can only processes tags. If there isn't a tag return any text.
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
            or namespace(elem.tag) != XHTML_NS:
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) == XHTML_NS \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) == XHTML_NS \
                     and elem.tail:
                 return [elem.tail]
             return ['']
diff --git a/src/calibre/ebooks/txt/txtml.py b/src/calibre/ebooks/txt/txtml.py
index 8326298071..31d172e9c9 100644
--- a/src/calibre/ebooks/txt/txtml.py
+++ b/src/calibre/ebooks/txt/txtml.py
@@ -10,8 +10,6 @@ import re
 
 from lxml import etree
 
-from polyglot.builtins import string_or_bytes
-
 BLOCK_TAGS = [
     'div',
     'p',
@@ -189,10 +187,10 @@ class TXTMLizer:
         '''
         from calibre.ebooks.oeb.base import XHTML_NS, barename, namespace
 
-        if not isinstance(elem.tag, string_or_bytes) \
+        if not isinstance(elem.tag, (str, bytes)) \
            or namespace(elem.tag) != XHTML_NS:
             p = elem.getparent()
-            if p is not None and isinstance(p.tag, string_or_bytes) and namespace(p.tag) == XHTML_NS \
+            if p is not None and isinstance(p.tag, (str, bytes)) and namespace(p.tag) == XHTML_NS \
                     and elem.tail:
                 return [elem.tail]
             return ['']
diff --git a/src/calibre/gui2/__init__.py b/src/calibre/gui2/__init__.py
index 9b58b6d961..1228d8c7a0 100644
--- a/src/calibre/gui2/__init__.py
+++ b/src/calibre/gui2/__init__.py
@@ -91,7 +91,7 @@ from calibre.utils.resources import get_image_path as I
 from calibre.utils.resources import get_path as P
 from calibre.utils.resources import user_dir
 from polyglot import queue
-from polyglot.builtins import iteritems, string_or_bytes
+from polyglot.builtins import iteritems
 
 del pqc, geometry_for_restore_as_dict
 NO_URL_FORMATTING = QUrl.UrlFormattingOption.None_
@@ -1487,7 +1487,7 @@ SanitizeLibraryPath = sanitize_env_vars  # For old plugins
 
 
 def open_url(qurl):
-    if isinstance(qurl, string_or_bytes):
+    if isinstance(qurl, (str, bytes)):
         qurl = QUrl(qurl)
     scheme = qurl.scheme().lower() or 'file'
     import fnmatch
@@ -1533,7 +1533,7 @@ def open_url(qurl):
 
 
 def safe_open_url(qurl):
-    if isinstance(qurl, string_or_bytes):
+    if isinstance(qurl, (str, bytes)):
         qurl = QUrl(qurl)
     if qurl.scheme() in ('', 'file'):
         path = qurl.toLocalFile()
diff --git a/src/calibre/gui2/actions/__init__.py b/src/calibre/gui2/actions/__init__.py
index 2bd5aa2cec..59721eee04 100644
--- a/src/calibre/gui2/actions/__init__.py
+++ b/src/calibre/gui2/actions/__init__.py
@@ -14,7 +14,6 @@ from calibre import prints
 from calibre.constants import ismacos
 from calibre.gui2 import Dispatcher
 from calibre.gui2.keyboard import NameConflict
-from polyglot.builtins import string_or_bytes
 
 
 def toolbar_widgets_for_action(gui, action):
@@ -244,7 +243,7 @@ class InterfaceAction(QObject):
         if attr == 'qaction':
             shortcut_action = ma
         if shortcut is not None:
-            keys = ((shortcut,) if isinstance(shortcut, string_or_bytes) else
+            keys = ((shortcut,) if isinstance(shortcut, (str, bytes)) else
                     tuple(shortcut))
             if shortcut_name is None:
                 if self.action_shortcut_name is not None:
@@ -324,7 +323,7 @@ class InterfaceAction(QObject):
             ac.setIcon(icon)
         keys = ()
         if shortcut is not None and shortcut is not False:
-            keys = ((shortcut,) if isinstance(shortcut, string_or_bytes) else
+            keys = ((shortcut,) if isinstance(shortcut, (str, bytes)) else
                     tuple(shortcut))
         unique_name = menu_action_unique_name(self, unique_name)
         if description is not None:
diff --git a/src/calibre/gui2/actions/add.py b/src/calibre/gui2/actions/add.py
index 3bb22c9784..ca883c3889 100644
--- a/src/calibre/gui2/actions/add.py
+++ b/src/calibre/gui2/actions/add.py
@@ -25,7 +25,6 @@ from calibre.utils.config_base import tweaks
 from calibre.utils.filenames import ascii_filename, make_long_path_useable
 from calibre.utils.icu import sort_key
 from calibre.utils.localization import ngettext
-from polyglot.builtins import string_or_bytes
 
 
 def get_filters():
@@ -541,7 +540,7 @@ class AddAction(InterfaceAction):
             self._add_extra_files({cid}, add_as_data_files)
 
     def __add_filesystem_book(self, paths, allow_device=True):
-        if isinstance(paths, string_or_bytes):
+        if isinstance(paths, (str, bytes)):
             paths = [paths]
         books = [path for path in map(os.path.abspath, paths) if os.access(path,
             os.R_OK)]
@@ -696,7 +695,7 @@ class AddAction(InterfaceAction):
             self.gui.device_job_exception(job)
             return
         paths = job.result
-        ok_paths = [x for x in paths if isinstance(x, string_or_bytes)]
+        ok_paths = [x for x in paths if isinstance(x, (str, bytes))]
         failed_paths = [x for x in paths if isinstance(x, tuple)]
         if failed_paths:
             if not ok_paths:
diff --git a/src/calibre/gui2/actions/similar_books.py b/src/calibre/gui2/actions/similar_books.py
index bc72d5c865..21345fa260 100644
--- a/src/calibre/gui2/actions/similar_books.py
+++ b/src/calibre/gui2/actions/similar_books.py
@@ -11,7 +11,6 @@ from qt.core import QToolButton
 from calibre.gui2.actions import InterfaceAction
 from calibre.startup import connect_lambda
 from calibre.utils.icu import lower as icu_lower
-from polyglot.builtins import string_or_bytes
 
 
 class SimilarBooksAction(InterfaceAction):
@@ -83,7 +82,7 @@ class SimilarBooksAction(InterfaceAction):
         if not val:
             return
 
-        if isinstance(val, string_or_bytes):
+        if isinstance(val, (str, bytes)):
             val = [val]
         if typ == 'authors':
             import re
diff --git a/src/calibre/gui2/add.py b/src/calibre/gui2/add.py
index 3edb7f114e..2e629839eb 100644
--- a/src/calibre/gui2/add.py
+++ b/src/calibre/gui2/add.py
@@ -35,12 +35,11 @@ from calibre.utils.filenames import make_long_path_useable
 from calibre.utils.icu import lower as icu_lower
 from calibre.utils.ipc.pool import Failure, Pool
 from calibre.utils.localization import ngettext
-from polyglot.builtins import string_or_bytes
 from polyglot.queue import Empty
 
 
 def validate_source(source, parent=None):  # {{{
-    if isinstance(source, string_or_bytes):
+    if isinstance(source, (str, bytes)):
         if not os.path.exists(source):
             error_dialog(parent, _('Cannot add books'), _(
                 'The path %s does not exist') % source, show=True)
@@ -210,7 +209,7 @@ class Adder(QObject):
             return tdir
 
         try:
-            if isinstance(self.source, string_or_bytes):
+            if isinstance(self.source, (str, bytes)):
                 find_files(self.source)
                 self.ignore_opf = True
             else:
diff --git a/src/calibre/gui2/ebook_download.py b/src/calibre/gui2/ebook_download.py
index d0288d04e3..0f247786bc 100644
--- a/src/calibre/gui2/ebook_download.py
+++ b/src/calibre/gui2/ebook_download.py
@@ -17,7 +17,7 @@ from calibre.gui2.threaded_jobs import ThreadedJob
 from calibre.ptempfile import PersistentTemporaryDirectory
 from calibre.utils.filenames import ascii_filename
 from calibre.web import get_download_filename_from_response
-from polyglot.builtins import as_unicode, string_or_bytes
+from polyglot.builtins import as_unicode
 
 
 class DownloadInfo(MessageBox):
@@ -157,7 +157,7 @@ class EbookDownloadMixin:
 
     def download_ebook(self, url='', cookie_file=None, filename='', save_loc='', add_to_lib=True, tags=[], create_browser=None):
         if tags:
-            if isinstance(tags, string_or_bytes):
+            if isinstance(tags, (str, bytes)):
                 tags = tags.split(',')
         start_ebook_download(Dispatcher(self.downloaded_ebook), self.job_manager, self, cookie_file, url, filename, save_loc, add_to_lib, tags, create_browser)
         self.status_bar.show_message(_('Downloading') + ' ' + as_unicode(filename or url, errors='replace'), 3000)
diff --git a/src/calibre/gui2/library/models.py b/src/calibre/gui2/library/models.py
index 24bf1c58b5..f37be2985d 100644
--- a/src/calibre/gui2/library/models.py
+++ b/src/calibre/gui2/library/models.py
@@ -49,7 +49,7 @@ from calibre.utils.icu import sort_key
 from calibre.utils.localization import calibre_langcode_to_name, ngettext
 from calibre.utils.resources import get_path as P
 from calibre.utils.search_query_parser import ParseException, SearchQueryParser
-from polyglot.builtins import iteritems, string_or_bytes
+from polyglot.builtins import iteritems
 
 Counts = namedtuple('Counts', 'library_total total current')
 
@@ -1481,7 +1481,7 @@ class OnDeviceSearch(SearchQueryParser):  # {{{
                     vals = accessor(row)
                     if vals is None:
                         vals = ''
-                    if isinstance(vals, string_or_bytes):
+                    if isinstance(vals, (str, bytes)):
                         vals = vals.split(',') if locvalue == 'collections' else [vals]
                     if _match(query, vals, m, use_primary_find_in_search=upf):
                         matches.add(index)
diff --git a/src/calibre/gui2/linux_file_dialogs.py b/src/calibre/gui2/linux_file_dialogs.py
index c9f018d2a5..07112916cb 100644
--- a/src/calibre/gui2/linux_file_dialogs.py
+++ b/src/calibre/gui2/linux_file_dialogs.py
@@ -13,7 +13,7 @@ from qt.core import QEventLoop
 from calibre import force_unicode
 from calibre.constants import DEBUG, filesystem_encoding, preferred_encoding
 from calibre.utils.config import dynamic
-from polyglot.builtins import reraise, string_or_bytes
+from polyglot.builtins import reraise
 
 
 def dialog_name(name, title):
@@ -78,7 +78,7 @@ def get_initial_dir(name, title, default_dir, no_save_dir):
         return ensure_dir(process_path(default_dir))
     key = dialog_name(name, title)
     saved = dynamic.get(key)
-    if not isinstance(saved, string_or_bytes):
+    if not isinstance(saved, (str, bytes)):
         saved = None
     if saved and os.path.isdir(saved):
         return ensure_dir(process_path(saved))
diff --git a/src/calibre/gui2/lrf_renderer/text.py b/src/calibre/gui2/lrf_renderer/text.py
index 9cd07197b9..08b6eaabae 100644
--- a/src/calibre/gui2/lrf_renderer/text.py
+++ b/src/calibre/gui2/lrf_renderer/text.py
@@ -12,7 +12,6 @@ from qt.core import QBrush, QColor, QFont, QFontMetrics, QGraphicsItem, QGraphic
 
 from calibre.ebooks.hyphenate import hyphenate_word
 from calibre.ebooks.lrf.fonts import LIBERATION_FONT_MAP
-from polyglot.builtins import string_or_bytes
 
 
 def WEIGHT_MAP(wt):
@@ -241,7 +240,7 @@ class TextBlock:
         open_containers = collections.deque()
         self.in_para = False
         for i in tb.content:
-            if isinstance(i, string_or_bytes):
+            if isinstance(i, (str, bytes)):
                 self.process_text(i)
             elif i is None:
                 if len(open_containers) > 0:
diff --git a/src/calibre/gui2/open_with.py b/src/calibre/gui2/open_with.py
index 11e4360c40..0693cccdea 100644
--- a/src/calibre/gui2/open_with.py
+++ b/src/calibre/gui2/open_with.py
@@ -39,7 +39,7 @@ from calibre.gui2.widgets2 import Dialog
 from calibre.utils.config import JSONConfig
 from calibre.utils.icu import numeric_sort_key as sort_key
 from calibre.utils.resources import get_image_path as I
-from polyglot.builtins import iteritems, string_or_bytes
+from polyglot.builtins import iteritems
 
 ENTRY_ROLE = Qt.ItemDataRole.UserRole
 
@@ -237,7 +237,7 @@ else:
 
     def entry_to_item(entry, parent):
         icon_path = entry.get('Icon') or I('blank.png')
-        if not isinstance(icon_path, string_or_bytes):
+        if not isinstance(icon_path, (str, bytes)):
             icon_path = I('blank.png')
         ans = QListWidgetItem(QIcon(icon_path), entry.get('Name') or _('Unknown'), parent)
         ans.setData(ENTRY_ROLE, entry)
diff --git a/src/calibre/gui2/preferences/__init__.py b/src/calibre/gui2/preferences/__init__.py
index 6ac66fa297..74c2afea74 100644
--- a/src/calibre/gui2/preferences/__init__.py
+++ b/src/calibre/gui2/preferences/__init__.py
@@ -31,7 +31,6 @@ from calibre.customize.ui import preferences_plugins
 from calibre.gui2.complete2 import EditWithComplete
 from calibre.gui2.widgets import HistoryLineEdit
 from calibre.utils.config import ConfigProxy
-from polyglot.builtins import string_or_bytes
 
 
 class AbortCommit(Exception):
@@ -190,7 +189,7 @@ class Setting:
             else:
                 self.gui_obj.clear()
                 for x in choices:
-                    if isinstance(x, string_or_bytes):
+                    if isinstance(x, (str, bytes)):
                         x = (x, x)
                     self.gui_obj.addItem(x[0], (x[1]))
         self.set_gui_val(self.get_config_val(default=False))
diff --git a/src/calibre/gui2/qt_file_dialogs.py b/src/calibre/gui2/qt_file_dialogs.py
index 6a06232bc2..684ed4ee12 100644
--- a/src/calibre/gui2/qt_file_dialogs.py
+++ b/src/calibre/gui2/qt_file_dialogs.py
@@ -7,7 +7,6 @@ import os
 from qt.core import QDialog, QFileDialog, QObject
 
 from calibre.gui2.linux_file_dialogs import dialog_name, image_extensions
-from polyglot.builtins import string_or_bytes
 from polyglot.urllib import unquote
 
 
@@ -89,7 +88,7 @@ class FileDialog(QObject):
         else:
             initial_dir = dynamic.get(self.dialog_name,
                     os.path.expanduser(default_dir))
-        if not isinstance(initial_dir, string_or_bytes):
+        if not isinstance(initial_dir, (str, bytes)):
             initial_dir = os.path.expanduser(default_dir)
         if not initial_dir or (not os.path.exists(initial_dir) and not (
                 mode == QFileDialog.FileMode.AnyFile and (no_save_dir or combine_file_and_saved_dir))):
diff --git a/src/calibre/gui2/search_box.py b/src/calibre/gui2/search_box.py
index 9b7fbd7e4c..78fa2d75f1 100644
--- a/src/calibre/gui2/search_box.py
+++ b/src/calibre/gui2/search_box.py
@@ -17,7 +17,7 @@ from calibre.gui2.dialogs.search import SearchDialog
 from calibre.gui2.widgets import stylesheet_for_lineedit
 from calibre.utils.icu import primary_sort_key
 from calibre.utils.localization import pgettext
-from polyglot.builtins import native_string_type, string_or_bytes
+from polyglot.builtins import native_string_type
 
 
 class AsYouType(str):
@@ -215,7 +215,7 @@ class SearchBox2(QComboBox):  # {{{
             self.parse_error_action.setToolTip(tooltip)
 
     def search_done(self, ok):
-        if isinstance(ok, string_or_bytes):
+        if isinstance(ok, (str, bytes)):
             self.setToolTip(ok)
             self.show_parse_error_action(True, tooltip=ok)
             ok = False
diff --git a/src/calibre/gui2/store/web_store.py b/src/calibre/gui2/store/web_store.py
index 14a3be9490..0538fd0bf0 100644
--- a/src/calibre/gui2/store/web_store.py
+++ b/src/calibre/gui2/store/web_store.py
@@ -20,7 +20,6 @@ from calibre.ptempfile import PersistentTemporaryDirectory, reset_base_dir
 from calibre.startup import connect_lambda
 from calibre.utils.webengine import setup_profile
 from polyglot.binary import as_base64_bytes, from_base64_bytes
-from polyglot.builtins import string_or_bytes
 
 
 class DownloadItem(QWidget):
@@ -213,7 +212,7 @@ class Main(MainWindow):
                 os.remove(path)
             return
         tags = self.data['tags']
-        if isinstance(tags, string_or_bytes):
+        if isinstance(tags, (str, bytes)):
             tags = list(filter(None, [x.strip() for x in tags.split(',')]))
         data = json.dumps({'path': path, 'tags': tags})
         if not isinstance(data, bytes):
diff --git a/src/calibre/gui2/tweak_book/boss.py b/src/calibre/gui2/tweak_book/boss.py
index 97ce2cec74..4bf552c7d5 100644
--- a/src/calibre/gui2/tweak_book/boss.py
+++ b/src/calibre/gui2/tweak_book/boss.py
@@ -88,7 +88,7 @@ from calibre.utils.imghdr import identify
 from calibre.utils.ipc.launch import exe_path, macos_edit_book_bundle_path
 from calibre.utils.localization import ngettext
 from calibre.utils.tdir_in_cache import tdir_in_cache
-from polyglot.builtins import as_bytes, iteritems, itervalues, string_or_bytes
+from polyglot.builtins import as_bytes, iteritems, itervalues
 from polyglot.urllib import urlparse
 
 _diff_dialogs = []
@@ -1565,7 +1565,7 @@ class Boss(QObject):
 
     @in_thread_job
     def export_requested(self, name_or_names, path):
-        if isinstance(name_or_names, string_or_bytes):
+        if isinstance(name_or_names, (str, bytes)):
             return self.export_file(name_or_names, path)
         for name in name_or_names:
             dest = os.path.abspath(os.path.join(path, name))
diff --git a/src/calibre/gui2/tweak_book/editor/widget.py b/src/calibre/gui2/tweak_book/editor/widget.py
index 9e9425595a..5e00b550e3 100644
--- a/src/calibre/gui2/tweak_book/editor/widget.py
+++ b/src/calibre/gui2/tweak_book/editor/widget.py
@@ -36,11 +36,10 @@ from calibre.gui2.tweak_book.editor import CLASS_ATTRIBUTE_PROPERTY, CSS_PROPERT
 from calibre.gui2.tweak_book.editor.help import help_url
 from calibre.gui2.tweak_book.editor.text import TextEdit
 from calibre.utils.icu import primary_sort_key, utf16_length
-from polyglot.builtins import string_or_bytes
 
 
 def create_icon(text, palette=None, sz=None, divider=2, fill='white'):
-    if isinstance(fill, string_or_bytes):
+    if isinstance(fill, (str, bytes)):
         fill = QColor(fill)
     sz = sz or math.ceil(tprefs['toolbar_icon_size'] * QApplication.instance().devicePixelRatio())
     if palette is None:
diff --git a/src/calibre/gui2/ui.py b/src/calibre/gui2/ui.py
index 34b5fd4163..fad9a32525 100644
--- a/src/calibre/gui2/ui.py
+++ b/src/calibre/gui2/ui.py
@@ -68,7 +68,6 @@ from calibre.utils.config import dynamic, prefs
 from calibre.utils.ipc.pool import Pool
 from calibre.utils.resources import get_image_path as I
 from calibre.utils.resources import get_path as P
-from polyglot.builtins import string_or_bytes
 from polyglot.queue import Empty, Queue
 
 
@@ -656,7 +655,7 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
 
     def handle_cli_args(self, args):
         from urllib.parse import parse_qs, unquote, urlparse
-        if isinstance(args, string_or_bytes):
+        if isinstance(args, (str, bytes)):
             args = [args]
         files, urls = [], []
         for p in args:
diff --git a/src/calibre/gui2/win_file_dialogs.py b/src/calibre/gui2/win_file_dialogs.py
index 785418f64a..9515e1445a 100644
--- a/src/calibre/gui2/win_file_dialogs.py
+++ b/src/calibre/gui2/win_file_dialogs.py
@@ -11,7 +11,6 @@ from threading import Thread
 from uuid import uuid4
 
 from calibre.utils.localization import _
-from polyglot.builtins import string_or_bytes
 
 base = sys.extensions_location if hasattr(sys, 'new_app_layout') else os.path.dirname(sys.executable)
 HELPER = os.path.join(base, 'calibre-file-dialog.exe')
@@ -74,7 +73,7 @@ def serialize_file_types(file_types):
         buf.append(struct.pack(f'=H{len(x)}s', len(x), x))
     for name, extensions in file_types:
         add(name or _('Files'))
-        if isinstance(extensions, string_or_bytes):
+        if isinstance(extensions, (str, bytes)):
             extensions = extensions.split()
         add('; '.join('*.' + ext.lower() for ext in extensions))
     return b''.join(buf)
diff --git a/src/calibre/library/catalogs/bibtex.py b/src/calibre/library/catalogs/bibtex.py
index d135fa5d8b..f5729cf58d 100644
--- a/src/calibre/library/catalogs/bibtex.py
+++ b/src/calibre/library/catalogs/bibtex.py
@@ -17,7 +17,6 @@ from calibre.customize.conversion import DummyReporter
 from calibre.ebooks.metadata import format_isbn
 from calibre.library.catalogs import FIELDS, TEMPLATE_ALLOWED_FIELDS
 from calibre.utils.localization import _
-from polyglot.builtins import string_or_bytes
 
 
 class BIBTEX(CatalogPlugin):
@@ -220,10 +219,10 @@ class BIBTEX(CatalogPlugin):
                     bibtex_entry.append(f'year = "{item.year}"')
                     bibtex_entry.append('month = "{}"'.format(bibtexdict.utf8ToBibtex(strftime('%b', item))))
 
-                elif field.startswith('#') and isinstance(item, string_or_bytes):
+                elif field.startswith('#') and isinstance(item, (str, bytes)):
                     bibtex_entry.append(f'custom_{field[1:]} = "{bibtexdict.utf8ToBibtex(item)}"')
 
-                elif isinstance(item, string_or_bytes):
+                elif isinstance(item, (str, bytes)):
                     # elif field in ['title', 'publisher', 'cover', 'uuid', 'ondevice',
                     # 'author_sort', 'series', 'title_sort'] :
                     bibtex_entry.append(f'{field} = "{bibtexdict.utf8ToBibtex(item)}"')
@@ -357,7 +356,7 @@ class BIBTEX(CatalogPlugin):
             bibtexc.ascii_bibtex = True
 
         # Check citation choice and go to default in case of bad CLI
-        if isinstance(opts.impcit, string_or_bytes):
+        if isinstance(opts.impcit, (str, bytes)):
             if opts.impcit == 'False':
                 citation_bibtex= False
             elif opts.impcit == 'True':
@@ -369,7 +368,7 @@ class BIBTEX(CatalogPlugin):
             citation_bibtex= opts.impcit
 
         # Check add file entry and go to default in case of bad CLI
-        if isinstance(opts.addfiles, string_or_bytes):
+        if isinstance(opts.addfiles, (str, bytes)):
             if opts.addfiles == 'False':
                 addfiles_bibtex = False
             elif opts.addfiles == 'True':
diff --git a/src/calibre/library/custom_columns.py b/src/calibre/library/custom_columns.py
index c85dba0dc3..d65def618d 100644
--- a/src/calibre/library/custom_columns.py
+++ b/src/calibre/library/custom_columns.py
@@ -16,7 +16,6 @@ from calibre.library.field_metadata import FieldMetadata
 from calibre.utils.config import tweaks
 from calibre.utils.date import parse_date
 from calibre.utils.localization import _
-from polyglot.builtins import string_or_bytes
 
 
 class CustomColumns:
@@ -218,7 +217,7 @@ class CustomColumns:
             ans = ans.split(data['multiple_seps']['cache_to_list']) if ans else []
             if data['display'].get('sort_alpha', False):
                 ans.sort(key=lambda x:x.lower())
-        if data['datatype'] == 'datetime' and isinstance(ans, string_or_bytes):
+        if data['datatype'] == 'datetime' and isinstance(ans, (str, bytes)):
             from calibre.db.tables import UNDEFINED_DATE, c_parse
             ans = c_parse(ans)
             if ans is UNDEFINED_DATE:
@@ -250,7 +249,7 @@ class CustomColumns:
             ans = ans.split(data['multiple_seps']['cache_to_list']) if ans else []
             if data['display'].get('sort_alpha', False):
                 ans.sort(key=lambda x: x.lower())
-        if data['datatype'] == 'datetime' and isinstance(ans, string_or_bytes):
+        if data['datatype'] == 'datetime' and isinstance(ans, (str, bytes)):
             from calibre.db.tables import UNDEFINED_DATE, c_parse
             ans = c_parse(ans)
             if ans is UNDEFINED_DATE:
diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 8306627307..92b50db429 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -55,7 +55,7 @@ from calibre.utils.localization import _, calibre_langcode_to_name, canonicalize
 from calibre.utils.recycle_bin import delete_file, delete_tree
 from calibre.utils.resources import get_path as P
 from calibre.utils.search_query_parser import saved_searches, set_saved_searches
-from polyglot.builtins import iteritems, string_or_bytes
+from polyglot.builtins import iteritems
 
 copyfile = os.link if hasattr(os, 'link') else shutil.copyfile
 SPOOL_SIZE = 30*1024*1024
@@ -1121,7 +1121,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
 
     def find_identical_books(self, mi):
         fuzzy_title_patterns = [(re.compile(pat, re.IGNORECASE) if
-            isinstance(pat, string_or_bytes) else pat, repl) for pat, repl in
+            isinstance(pat, (str, bytes)) else pat, repl) for pat, repl in
                 [
                     (r'[\[\](){}<>\'";,:#]', ''),
                     (get_title_sort_pat(), ''),
@@ -1404,7 +1404,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
             id_ = index if index_is_id else self.id(index)
             raise NoSuchFormat(f'Record {id_} has no {fmt} file')
         if windows_atomic_move is not None:
-            if not isinstance(dest, string_or_bytes):
+            if not isinstance(dest, (str, bytes)):
                 raise Exception('Error, you must pass the dest as a path when'
                         ' using windows_atomic_move')
             if dest:
@@ -1459,7 +1459,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
         id = index if index_is_id else self.id(index)
         path = os.path.join(self.library_path, self.path(id, index_is_id=True), 'cover.jpg')
         if windows_atomic_move is not None:
-            if not isinstance(dest, string_or_bytes):
+            if not isinstance(dest, (str, bytes)):
                 raise Exception('Error, you must pass the dest as a path when'
                         ' using windows_atomic_move')
             if os.access(path, os.R_OK) and dest and not samefile(dest, path):
@@ -2340,7 +2340,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
         # force_changes has no effect on cover manipulation
         if mi.cover_data[1] is not None:
             doit(self.set_cover, id, mi.cover_data[1], commit=False)
-        elif isinstance(mi.cover, string_or_bytes) and mi.cover:
+        elif isinstance(mi.cover, (str, bytes)) and mi.cover:
             if os.access(mi.cover, os.R_OK):
                 with open(mi.cover, 'rb') as f:
                     raw = f.read()
@@ -2647,7 +2647,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
     def set_pubdate(self, id, dt, notify=True, commit=True):
         if not dt:
             dt = UNDEFINED_DATE
-        if isinstance(dt, string_or_bytes):
+        if isinstance(dt, (str, bytes)):
             dt = parse_only_date(dt)
         self.conn.execute('UPDATE books SET pubdate=? WHERE id=?', (dt, id))
         self.data.set(id, self.FIELD_MAP['pubdate'], dt, row_is_id=True)
diff --git a/src/calibre/srv/ajax.py b/src/calibre/srv/ajax.py
index 87eae7ceef..460b05a2a5 100644
--- a/src/calibre/srv/ajax.py
+++ b/src/calibre/srv/ajax.py
@@ -21,7 +21,7 @@ from calibre.utils.config import prefs, tweaks
 from calibre.utils.date import isoformat, timestampfromdt
 from calibre.utils.icu import numeric_sort_key as sort_key
 from calibre.utils.localization import _
-from polyglot.builtins import iteritems, string_or_bytes
+from polyglot.builtins import iteritems
 
 
 def ensure_val(x, *allowed):
@@ -107,7 +107,7 @@ def book_to_json(ctx, rd, db, book_id,
                 if (fm and fm['is_category'] and not fm['is_csp'] and
                         key != 'formats' and fm['datatype'] != 'rating'):
                     categories = mi.get(key) or []
-                    if isinstance(categories, string_or_bytes):
+                    if isinstance(categories, (str, bytes)):
                         categories = [categories]
                     category_urls[key] = dbtags = {}
                     for category in categories:
diff --git a/src/calibre/srv/http_response.py b/src/calibre/srv/http_response.py
index c93be0202c..d9ccb9cb28 100644
--- a/src/calibre/srv/http_response.py
+++ b/src/calibre/srv/http_response.py
@@ -25,7 +25,7 @@ from calibre.srv.utils import HTTP1, HTTP11, Cookie, MultiDict, get_translator_f
 from calibre.utils.monotonic import monotonic
 from calibre.utils.speedups import ReadOnlyFileBuffer
 from polyglot import http_client, reprlib
-from polyglot.builtins import error_message, iteritems, reraise, string_or_bytes
+from polyglot.builtins import error_message, iteritems, reraise
 
 Range = namedtuple('Range', 'start stop size')
 MULTIPART_SEPARATOR = uuid.uuid4().hex
@@ -315,7 +315,7 @@ def filesystem_file_output(output, outheaders, stat_result):
     etag = getattr(output, 'etag', None)
     if etag is None:
         oname = output.name or ''
-        if not isinstance(oname, string_or_bytes):
+        if not isinstance(oname, (str, bytes)):
             oname = str(oname)
         etag = hashlib.sha1((str(stat_result.st_mtime) + force_unicode(oname)).encode('utf-8')).hexdigest()
     else:
@@ -652,7 +652,7 @@ class HTTPConnection(HTTPRequest):
             output = filesystem_file_output(output, outheaders, stat_result)
             if 'Content-Type' not in outheaders:
                 output_name = output.name
-                if not isinstance(output_name, string_or_bytes):
+                if not isinstance(output_name, (str, bytes)):
                     output_name = str(output_name)
                 mt = guess_type(output_name)[0]
                 if mt:
@@ -661,7 +661,7 @@ class HTTPConnection(HTTPRequest):
                     outheaders['Content-Type'] = mt
                 else:
                     outheaders['Content-Type'] = 'application/octet-stream'
-        elif isinstance(output, string_or_bytes):
+        elif isinstance(output, (str, bytes)):
             output = dynamic_output(output, outheaders)
         elif hasattr(output, 'read'):
             output = ReadableOutput(output)
diff --git a/src/calibre/srv/legacy.py b/src/calibre/srv/legacy.py
index 4e7021544a..18d1e4e055 100644
--- a/src/calibre/srv/legacy.py
+++ b/src/calibre/srv/legacy.py
@@ -18,14 +18,14 @@ from calibre.srv.utils import get_library_data, http_date
 from calibre.utils.cleantext import clean_xml_chars
 from calibre.utils.date import dt_as_local, is_date_undefined, timestampfromdt
 from calibre.utils.localization import _
-from polyglot.builtins import as_bytes, string_or_bytes
+from polyglot.builtins import as_bytes
 from polyglot.urllib import urlencode
 
 # /mobile {{{
 
 
 def clean(x):
-    if isinstance(x, string_or_bytes):
+    if isinstance(x, (str, bytes)):
         x = clean_xml_chars(x)
     return x
 
diff --git a/src/calibre/utils/img.py b/src/calibre/utils/img.py
index eee127a1a7..a26a5bddc2 100644
--- a/src/calibre/utils/img.py
+++ b/src/calibre/utils/img.py
@@ -22,7 +22,6 @@ from calibre.utils.filenames import atomic_rename
 from calibre.utils.imghdr import what
 from calibre.utils.resources import get_image_path as I
 from calibre_extensions import imageops
-from polyglot.builtins import string_or_bytes
 
 
 # Utilities {{{
@@ -515,7 +514,7 @@ def quantize_image(img, max_colors=256, dither=True, palette=''):
     img = image_from_data(img)
     if img.hasAlphaChannel():
         img = blend_image(img)
-    if palette and isinstance(palette, string_or_bytes):
+    if palette and isinstance(palette, (str, bytes)):
         palette = palette.split()
     return imageops.quantize(img, int(max_colors), dither, tuple(QColor(x).rgb() for x in palette))
 
diff --git a/src/calibre/utils/imghdr.py b/src/calibre/utils/imghdr.py
index 74d3874740..1b704622cc 100644
--- a/src/calibre/utils/imghdr.py
+++ b/src/calibre/utils/imghdr.py
@@ -6,7 +6,6 @@ import os
 from struct import error, unpack
 
 from calibre.utils.speedups import ReadOnlyFileBuffer
-from polyglot.builtins import string_or_bytes
 
 ''' Recognize image file formats and sizes based on their first few bytes.'''
 
@@ -16,7 +15,7 @@ HSIZE = 120
 def what(file, h=None):
     ' Recognize image headers '
     if h is None:
-        if isinstance(file, string_or_bytes):
+        if isinstance(file, (str, bytes)):
             with open(file, 'rb') as f:
                 h = f.read(HSIZE)
         else:
diff --git a/src/calibre/utils/ipc/launch.py b/src/calibre/utils/ipc/launch.py
index 53465ac97a..1233835dfa 100644
--- a/src/calibre/utils/ipc/launch.py
+++ b/src/calibre/utils/ipc/launch.py
@@ -14,7 +14,7 @@ from calibre.ptempfile import PersistentTemporaryFile, base_dir
 from calibre.utils.config import prefs
 from calibre.utils.serialize import msgpack_dumps
 from polyglot.binary import as_hex_unicode
-from polyglot.builtins import environ_item, native_string_type, string_or_bytes
+from polyglot.builtins import environ_item, native_string_type
 
 if iswindows:
     try:
@@ -184,7 +184,7 @@ class Worker:
         _cwd = cwd
         if priority is None:
             priority = prefs['worker_process_priority']
-        cmd = [exe] if isinstance(exe, string_or_bytes) else exe
+        cmd = [exe] if isinstance(exe, (str, bytes)) else exe
         args = {
                 'env': env,
                 'cwd': _cwd,
diff --git a/src/calibre/utils/ipc/server.py b/src/calibre/utils/ipc/server.py
index 808a392718..c2f8f58abb 100644
--- a/src/calibre/utils/ipc/server.py
+++ b/src/calibre/utils/ipc/server.py
@@ -25,7 +25,7 @@ from calibre.utils.ipc.launch import Worker
 from calibre.utils.ipc.worker import PARALLEL_FUNCS
 from calibre.utils.serialize import pickle_loads
 from polyglot.binary import as_hex_unicode
-from polyglot.builtins import environ_item, string_or_bytes
+from polyglot.builtins import environ_item
 from polyglot.queue import Empty, Queue
 
 server_counter = count()
@@ -125,7 +125,7 @@ class Server(Thread):
             redirect_output = not gui
 
         cw = self.do_launch(gui, redirect_output, rfile, job_name=job_name)
-        if isinstance(cw, string_or_bytes):
+        if isinstance(cw, (str, bytes)):
             raise CriticalError('Failed to launch worker process:\n'+force_unicode(cw))
         if DEBUG:
             print(f'Worker Launch took: {time.monotonic() - start:.2f} seconds')
diff --git a/src/calibre/utils/ipc/simple_worker.py b/src/calibre/utils/ipc/simple_worker.py
index 5a336979e7..b1cb3ca66b 100644
--- a/src/calibre/utils/ipc/simple_worker.py
+++ b/src/calibre/utils/ipc/simple_worker.py
@@ -16,7 +16,7 @@ from calibre.constants import iswindows
 from calibre.utils.ipc import eintr_retry_call
 from calibre.utils.ipc.launch import Worker, windows_creationflags_for_worker_process
 from calibre.utils.monotonic import monotonic
-from polyglot.builtins import environ_item, string_or_bytes
+from polyglot.builtins import environ_item
 
 if iswindows:
     from multiprocessing.connection import PipeConnection as Connection
@@ -153,7 +153,7 @@ def start_pipe_worker(command, env=None, priority='normal', **process_args):
             args['env']['CALIBRE_WORKER_NICENESS'] = str(niceness)
 
         exe = w.executable
-        cmd = [exe] if isinstance(exe, string_or_bytes) else exe
+        cmd = [exe] if isinstance(exe, (str, bytes)) else exe
         p = subprocess.Popen(cmd + ['--pipe-worker', command], **args)
     finally:
         if iswindows and pass_fds:
diff --git a/src/calibre/utils/open_with/osx.py b/src/calibre/utils/open_with/osx.py
index 7d8a08aac3..48f8465b76 100644
--- a/src/calibre/utils/open_with/osx.py
+++ b/src/calibre/utils/open_with/osx.py
@@ -13,7 +13,6 @@ from plistlib import loads
 
 from calibre.ptempfile import TemporaryDirectory
 from calibre.utils.icu import numeric_sort_key
-from polyglot.builtins import string_or_bytes
 
 application_locations = ('/Applications', '~/Applications', '~/Desktop')
 
@@ -241,7 +240,7 @@ def get_extensions_from_utis(utis, plist):
         for decl in plist.get(key, ()):
             if isinstance(decl, dict):
                 uti = decl.get('UTTypeIdentifier')
-                if isinstance(uti, string_or_bytes):
+                if isinstance(uti, (str, bytes)):
                     spec = decl.get('UTTypeTagSpecification')
                     if isinstance(spec, dict):
                         ext = spec.get('public.filename-extension')
@@ -291,10 +290,10 @@ def get_bundle_data(path):
             extensions |= get_extensions_from_utis(utis, plist)
         else:
             for ext in dtype.get('CFBundleTypeExtensions', ()):
-                if isinstance(ext, string_or_bytes):
+                if isinstance(ext, (str, bytes)):
                     extensions.add(ext.lower())
             for mt in dtype.get('CFBundleTypeMIMETypes', ()):
-                if isinstance(mt, string_or_bytes):
+                if isinstance(mt, (str, bytes)):
                     for ext in mimetypes.guess_all_extensions(mt, strict=False):
                         extensions.add(ext.lower())
     return ans
diff --git a/src/calibre/utils/smtplib.py b/src/calibre/utils/smtplib.py
index bd201a3a25..57c429f91d 100644
--- a/src/calibre/utils/smtplib.py
+++ b/src/calibre/utils/smtplib.py
@@ -53,8 +53,6 @@ from email.base64mime import body_encode as encode_base64
 from functools import partial
 from sys import stderr
 
-from polyglot.builtins import string_or_bytes
-
 __all__ = [
     'SMTP',
     'SMTPAuthenticationError',
@@ -735,7 +733,7 @@ class SMTP:
             self.rset()
             raise SMTPSenderRefused(code, resp, from_addr)
         senderrs = {}
-        if isinstance(to_addrs, string_or_bytes):
+        if isinstance(to_addrs, (str, bytes)):
             to_addrs = [to_addrs]
         for each in to_addrs:
             code, resp = self.rcpt(each, rcpt_options)
diff --git a/src/calibre/utils/unrar.py b/src/calibre/utils/unrar.py
index 53423ef15a..9343ed4c1d 100644
--- a/src/calibre/utils/unrar.py
+++ b/src/calibre/utils/unrar.py
@@ -13,7 +13,6 @@ from io import BytesIO
 from calibre.constants import filesystem_encoding, iswindows
 from calibre.ptempfile import PersistentTemporaryFile, TemporaryDirectory
 from calibre.utils.filenames import make_long_path_useable
-from polyglot.builtins import string_or_bytes
 
 
 def as_unicode(x):
@@ -29,7 +28,7 @@ class StreamAsPath:
 
     def __enter__(self):
         self.temppath = None
-        if isinstance(self.stream, string_or_bytes):
+        if isinstance(self.stream, (str, bytes)):
             return as_unicode(self.stream)
         name = getattr(self.stream, 'name', None)
         if name and os.access(name, os.R_OK):
diff --git a/src/calibre/utils/zipfile.py b/src/calibre/utils/zipfile.py
index 43ccf12f5c..efa7fa5c13 100644
--- a/src/calibre/utils/zipfile.py
+++ b/src/calibre/utils/zipfile.py
@@ -20,7 +20,7 @@ from calibre import sanitize_file_name
 from calibre.constants import filesystem_encoding
 from calibre.ebooks.chardet import detect
 from calibre.ptempfile import SpooledTemporaryFile
-from polyglot.builtins import as_bytes, string_or_bytes
+from polyglot.builtins import as_bytes
 
 try:
     from calibre_extensions.speedup import pread_all
@@ -782,7 +782,7 @@ class ZipFile:
         self.comment = b''
 
         # Check if we were passed a file-like object
-        if isinstance(file, string_or_bytes):
+        if isinstance(file, (str, bytes)):
             self._filePassed = 0
             self.filename = file
             modeDict = {'r': 'rb', 'w': 'wb', 'a': 'r+b'}
diff --git a/src/calibre/web/feeds/__init__.py b/src/calibre/web/feeds/__init__.py
index 266ded702a..3d9f1895fc 100644
--- a/src/calibre/web/feeds/__init__.py
+++ b/src/calibre/web/feeds/__init__.py
@@ -16,7 +16,6 @@ from calibre import force_unicode, replace_entities, strftime
 from calibre.utils.cleantext import clean_ascii_chars, clean_xml_chars
 from calibre.utils.date import dt_factory, local_tz, utcnow
 from calibre.utils.logging import default_log
-from polyglot.builtins import string_or_bytes
 
 
 class Article:
@@ -25,7 +24,7 @@ class Article:
         from lxml import html
         self.downloaded = False
         self.id = id
-        if not title or not isinstance(title, string_or_bytes):
+        if not title or not isinstance(title, (str, bytes)):
             title = _('Unknown')
         title = force_unicode(title, 'utf-8')
         self._title = clean_xml_chars(title).strip()
diff --git a/src/calibre/web/feeds/news.py b/src/calibre/web/feeds/news.py
index 1306623c72..a5c508989d 100644
--- a/src/calibre/web/feeds/news.py
+++ b/src/calibre/web/feeds/news.py
@@ -33,7 +33,6 @@ from calibre.web.feeds import Feed, feed_from_xml, feeds_from_index, templates
 from calibre.web.fetch.simple import AbortArticle, RecursiveFetcher
 from calibre.web.fetch.simple import option_parser as web2disk_option_parser
 from calibre.web.fetch.utils import prepare_masthead_image
-from polyglot.builtins import string_or_bytes
 
 
 def classes(classes):
@@ -1751,7 +1750,7 @@ class BasicNewsRecipe(Recipe):
         parsed_feeds = []
         br = self.browser
         for obj in feeds:
-            if isinstance(obj, string_or_bytes):
+            if isinstance(obj, (str, bytes)):
                 title, url = None, obj
             else:
                 title, url = obj
@@ -1812,7 +1811,7 @@ class BasicNewsRecipe(Recipe):
         '''
         if tag is None:
             return ''
-        if isinstance(tag, string_or_bytes):
+        if isinstance(tag, (str, bytes)):
             return tag
         if callable(getattr(tag, 'xpath', None)) and not hasattr(tag, 'contents'):  # a lxml tag
             from lxml.etree import tostring
diff --git a/src/odf/attrconverters.py b/src/odf/attrconverters.py
index 3ed1d85128..58a14c975e 100644
--- a/src/odf/attrconverters.py
+++ b/src/odf/attrconverters.py
@@ -19,7 +19,7 @@
 
 import re
 
-from polyglot.builtins import string_or_bytes, unicode_type
+from polyglot.builtins import unicode_type
 
 from .namespaces import (
     ANIMNS,
@@ -212,7 +212,7 @@ def cnv_NCName(attribute, arg, element):
     ''' NCName is defined in http://www.w3.org/TR/REC-xml-names/#NT-NCName
         Essentially an XML name minus ':'
     '''
-    if isinstance(arg, string_or_bytes):
+    if isinstance(arg, (str, bytes)):
         return make_NCName(arg)
     else:
         return arg.getAttrNS(STYLENS, 'name')
@@ -269,7 +269,7 @@ pattern_points = re.compile(r'-?[0-9]+,-?[0-9]+([ ]+-?[0-9]+,-?[0-9]+)*')
 
 def cnv_points(attribute, arg, element):
     global pattern_points
-    if isinstance(arg, string_or_bytes):
+    if isinstance(arg, (str, bytes)):
         if not pattern_points.match(arg):
             raise ValueError('x,y are separated by a comma and the points are separated by white spaces')
         return arg