diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 195490e3a8..e841bde57c 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -4,7 +4,8 @@ on:
   merge_group:
   push:
     branches-ignore:
-    - gh-readonly-queue/**  # Temporary merge queue-related GH-made branches
+    # disabled for jaraco/skeleton#103
+    # - gh-readonly-queue/**  # Temporary merge queue-related GH-made branches
   pull_request:
   workflow_dispatch:
 
diff --git a/README.rst b/README.rst
index c7387deb9f..f9f497d462 100644
--- a/README.rst
+++ b/README.rst
@@ -27,10 +27,9 @@
    :target: https://discord.com/channels/803025117553754132/815945031150993468
    :alt: Discord
 
-See the `Installation Instructions
-<https://packaging.python.org/installing/>`_ in the Python Packaging
-User's Guide for instructions on installing, upgrading, and uninstalling
-Setuptools.
+See the `Quickstart <https://setuptools.pypa.io/en/latest/userguide/quickstart.html>`_
+and the `User's Guide <https://setuptools.pypa.io/en/latest/userguide/>`_ for
+instructions on how to use Setuptools.
 
 Questions and comments should be directed to `GitHub Discussions
 <https://github.com/pypa/setuptools/discussions>`_.
diff --git a/pkg_resources/__init__.py b/pkg_resources/__init__.py
index 14680a476a..5bee50539d 100644
--- a/pkg_resources/__init__.py
+++ b/pkg_resources/__init__.py
@@ -399,20 +399,18 @@ def get_provider(moduleOrReq):
     return _find_adapter(_provider_factories, loader)(module)
 
 
-def _macos_vers(_cache=[]):
-    if not _cache:
-        version = platform.mac_ver()[0]
-        # fallback for MacPorts
-        if version == '':
-            plist = '/System/Library/CoreServices/SystemVersion.plist'
-            if os.path.exists(plist):
-                if hasattr(plistlib, 'readPlist'):
-                    plist_content = plistlib.readPlist(plist)
-                    if 'ProductVersion' in plist_content:
-                        version = plist_content['ProductVersion']
-
-        _cache.append(version.split('.'))
-    return _cache[0]
+@functools.lru_cache(maxsize=None)
+def _macos_vers():
+    version = platform.mac_ver()[0]
+    # fallback for MacPorts
+    if version == '':
+        plist = '/System/Library/CoreServices/SystemVersion.plist'
+        if os.path.exists(plist):
+            with open(plist, 'rb') as fh:
+                plist_content = plistlib.load(fh)
+            if 'ProductVersion' in plist_content:
+                version = plist_content['ProductVersion']
+    return version.split('.')
 
 
 def _macos_arch(machine):
@@ -1887,7 +1885,7 @@ def _extract_resource(self, manager, zip_path):  # noqa: C901
             try:
                 rename(tmpnam, real_path)
 
-            except os.error:
+            except OSError:
                 if os.path.isfile(real_path):
                     if self._is_current(real_path, zip_path):
                         # the file became current since it was checked above,
@@ -1900,7 +1898,7 @@ def _extract_resource(self, manager, zip_path):  # noqa: C901
                         return real_path
                 raise
 
-        except os.error:
+        except OSError:
             # report a user-friendly error
             manager.extraction_error()
 
@@ -2414,12 +2412,9 @@ def _cygwin_patch(filename):  # pragma: nocover
     return os.path.abspath(filename) if sys.platform == 'cygwin' else filename
 
 
-def _normalize_cached(filename, _cache={}):
-    try:
-        return _cache[filename]
-    except KeyError:
-        _cache[filename] = result = normalize_path(filename)
-        return result
+@functools.lru_cache(maxsize=None)
+def _normalize_cached(filename):
+    return normalize_path(filename)
 
 
 def _is_egg_path(path):
@@ -2893,7 +2888,7 @@ def __getattr__(self, attr):
 
     def __dir__(self):
         return list(
-            set(super(Distribution, self).__dir__())
+            set(super().__dir__())
             | set(attr for attr in self._provider.__dir__() if not attr.startswith('_'))
         )
 
@@ -3160,7 +3155,7 @@ class RequirementParseError(packaging.requirements.InvalidRequirement):
 class Requirement(packaging.requirements.Requirement):
     def __init__(self, requirement_string):
         """DO NOT CALL THIS UNDOCUMENTED METHOD; use Requirement.parse()!"""
-        super(Requirement, self).__init__(requirement_string)
+        super().__init__(requirement_string)
         self.unsafe_name = self.name
         project_name = safe_name(self.name)
         self.project_name, self.key = project_name, project_name.lower()
diff --git a/pkg_resources/tests/test_pkg_resources.py b/pkg_resources/tests/test_pkg_resources.py
index e316cd18ad..c667215c37 100644
--- a/pkg_resources/tests/test_pkg_resources.py
+++ b/pkg_resources/tests/test_pkg_resources.py
@@ -1,3 +1,4 @@
+import builtins
 import sys
 import tempfile
 import os
@@ -308,6 +309,32 @@ def test_dist_info_is_not_dir(tmp_path, only):
     assert not pkg_resources.dist_factory(str(tmp_path), str(dist_info), only)
 
 
+def test_macos_vers_fallback(monkeypatch, tmp_path):
+    """Regression test for pkg_resources._macos_vers"""
+    orig_open = builtins.open
+
+    # Pretend we need to use the plist file
+    monkeypatch.setattr('platform.mac_ver', mock.Mock(return_value=('', (), '')))
+
+    # Create fake content for the fake plist file
+    with open(tmp_path / 'fake.plist', 'wb') as fake_file:
+        plistlib.dump({"ProductVersion": "11.4"}, fake_file)
+
+    # Pretend the fake file exists
+    monkeypatch.setattr('os.path.exists', mock.Mock(return_value=True))
+
+    def fake_open(file, *args, **kwargs):
+        return orig_open(tmp_path / 'fake.plist', *args, **kwargs)
+
+    # Ensure that the _macos_vers works correctly
+    with mock.patch('builtins.open', mock.Mock(side_effect=fake_open)) as m:
+        pkg_resources._macos_vers.cache_clear()
+        assert pkg_resources._macos_vers() == ["11", "4"]
+        pkg_resources._macos_vers.cache_clear()
+
+    m.assert_called()
+
+
 class TestDeepVersionLookupDistutils:
     @pytest.fixture
     def env(self, tmpdir):
diff --git a/pkg_resources/tests/test_working_set.py b/pkg_resources/tests/test_working_set.py
index f8e60e752a..57f62b5492 100644
--- a/pkg_resources/tests/test_working_set.py
+++ b/pkg_resources/tests/test_working_set.py
@@ -76,10 +76,10 @@ def parametrize_test_working_set_resolve(*test_list):
             requirements,
             expected1,
             expected2,
-        ) = [
+        ) = (
             strip_comments(s.lstrip())
             for s in textwrap.dedent(test).lstrip().split('\n\n', 5)
-        ]
+        )
         installed_dists = list(parse_distributions(installed_dists))
         installable_dists = list(parse_distributions(installable_dists))
         requirements = list(pkg_resources.parse_requirements(requirements))
diff --git a/ruff.toml b/ruff.toml
index 7ed133b790..18776ab60a 100644
--- a/ruff.toml
+++ b/ruff.toml
@@ -1,5 +1,5 @@
 [lint]
-extend-ignore = [
+ignore = [
 	# https://docs.astral.sh/ruff/formatter/#conflicting-lint-rules
 	"W191",
 	"E111",
@@ -16,7 +16,27 @@ extend-ignore = [
 	"ISC001",
 	"ISC002",
 ]
+extend-select = [
+	"UP",  # pyupgrade
+]
+extend-ignore = [
+	"UP015",  # redundant-open-modes, explicit is prefered
+	"UP030",  # temporarily disabled
+	"UP031",  # temporarily disabled
+	"UP032",  # temporarily disabled
+	"UP036",  # temporarily disabled
+]
+exclude = [
+	"**/_vendor",
+	"setuptools/_distutils",
+	"setuptools/config/_validate_pyproject",
+]
 
 [format]
+exclude = [
+	"**/_vendor",
+	"setuptools/_distutils",
+	"setuptools/config/_validate_pyproject",
+]
 # https://docs.astral.sh/ruff/settings/#format-quote-style
 quote-style = "preserve"
diff --git a/setuptools/build_meta.py b/setuptools/build_meta.py
index 80ccceff3c..62954b3b77 100644
--- a/setuptools/build_meta.py
+++ b/setuptools/build_meta.py
@@ -121,7 +121,7 @@ def _file_with_extension(directory, extension):
         raise ValueError(
             'No distribution was found. Ensure that `setup.py` '
             'is not empty and that it calls `setup()`.'
-        )
+        ) from None
     return file
 
 
@@ -477,7 +477,7 @@ def run_setup(self, setup_script='setup.py'):
         sys.argv[0] = setup_script
 
         try:
-            super(_BuildMetaLegacyBackend, self).run_setup(setup_script=setup_script)
+            super().run_setup(setup_script=setup_script)
         finally:
             # While PEP 517 frontends should be calling each hook in a fresh
             # subprocess according to the standard (and thus it should not be
diff --git a/setuptools/command/bdist_egg.py b/setuptools/command/bdist_egg.py
index 87ba043fa0..8aaf155833 100644
--- a/setuptools/command/bdist_egg.py
+++ b/setuptools/command/bdist_egg.py
@@ -321,8 +321,7 @@ def walk_egg(egg_dir):
     if 'EGG-INFO' in dirs:
         dirs.remove('EGG-INFO')
     yield base, dirs, files
-    for bdf in walker:
-        yield bdf
+    yield from walker
 
 
 def analyze_egg(egg_dir, stubs):
@@ -403,14 +402,12 @@ def scan_module(egg_dir, base, name, stubs):
 
 def iter_symbols(code):
     """Yield names and strings used by `code` and its nested code objects"""
-    for name in code.co_names:
-        yield name
+    yield from code.co_names
     for const in code.co_consts:
         if isinstance(const, str):
             yield const
         elif isinstance(const, CodeType):
-            for name in iter_symbols(const):
-                yield name
+            yield from iter_symbols(const)
 
 
 def can_scan():
diff --git a/setuptools/command/build_ext.py b/setuptools/command/build_ext.py
index 2e1954ab0f..ef2a4da84d 100644
--- a/setuptools/command/build_ext.py
+++ b/setuptools/command/build_ext.py
@@ -157,7 +157,7 @@ def get_ext_filename(self, fullname):
 
         if fullname in self.ext_map:
             ext = self.ext_map[fullname]
-            use_abi3 = getattr(ext, 'py_limited_api') and get_abi3_suffix()
+            use_abi3 = ext.py_limited_api and get_abi3_suffix()
             if use_abi3:
                 filename = filename[: -len(so_ext)]
                 so_ext = get_abi3_suffix()
diff --git a/setuptools/command/build_py.py b/setuptools/command/build_py.py
index cbdd05aab0..3f40b060b3 100644
--- a/setuptools/command/build_py.py
+++ b/setuptools/command/build_py.py
@@ -288,7 +288,7 @@ def exclude_data_files(self, package, src_dir, files):
         return list(unique_everseen(keepers))
 
     @staticmethod
-    def _get_platform_patterns(spec, package, src_dir, extra_patterns=[]):
+    def _get_platform_patterns(spec, package, src_dir, extra_patterns=()):
         """
         yield platform-specific path patterns (suitable for glob
         or fn_match) from a glob-based spec (such as
diff --git a/setuptools/command/easy_install.py b/setuptools/command/easy_install.py
index e2859e8d35..f73d857f08 100644
--- a/setuptools/command/easy_install.py
+++ b/setuptools/command/easy_install.py
@@ -1744,8 +1744,7 @@ class RewritePthDistributions(PthDistributions):
     @classmethod
     def _wrap_lines(cls, lines):
         yield cls.prelude
-        for line in lines:
-            yield line
+        yield from lines
         yield cls.postlude
 
     prelude = _one_liner(
@@ -2025,7 +2024,7 @@ def chmod(path, mode):
     log.debug("changing mode of %s to %o", path, mode)
     try:
         _chmod(path, mode)
-    except os.error as e:
+    except OSError as e:
         log.debug("chmod failed: %s", e)
 
 
@@ -2181,8 +2180,7 @@ def get_args(cls, dist, header=None):
                 cls._ensure_safe_name(name)
                 script_text = cls.template % locals()
                 args = cls._get_script_args(type_, name, header, script_text)
-                for res in args:
-                    yield res
+                yield from args
 
     @staticmethod
     def _ensure_safe_name(name):
diff --git a/setuptools/command/editable_wheel.py b/setuptools/command/editable_wheel.py
index a3681f6cbc..8a4ae7928f 100644
--- a/setuptools/command/editable_wheel.py
+++ b/setuptools/command/editable_wheel.py
@@ -19,7 +19,7 @@
 from contextlib import suppress
 from enum import Enum
 from inspect import cleandoc
-from itertools import chain
+from itertools import chain, starmap
 from pathlib import Path
 from tempfile import TemporaryDirectory
 from typing import (
@@ -394,7 +394,7 @@ def __init__(self, dist: Distribution, name: str, path_entries: List[Path]):
         self.path_entries = path_entries
 
     def __call__(self, wheel: "WheelFile", files: List[str], mapping: Dict[str, str]):
-        entries = "\n".join((str(p.resolve()) for p in self.path_entries))
+        entries = "\n".join(str(p.resolve()) for p in self.path_entries)
         contents = _encode_pth(f"{entries}\n")
         wheel.writestr(f"__editable__.{self.name}.pth", contents)
 
@@ -600,7 +600,7 @@ def _simple_layout(
     layout = {pkg: find_package_path(pkg, package_dir, project_dir) for pkg in packages}
     if not layout:
         return set(package_dir) in ({}, {""})
-    parent = os.path.commonpath([_parent_path(k, v) for k, v in layout.items()])
+    parent = os.path.commonpath(starmap(_parent_path, layout.items()))
     return all(
         _path.same_path(Path(parent, *key.split('.')), value)
         for key, value in layout.items()
diff --git a/setuptools/command/egg_info.py b/setuptools/command/egg_info.py
index 7169f33535..62d2feea9b 100644
--- a/setuptools/command/egg_info.py
+++ b/setuptools/command/egg_info.py
@@ -385,9 +385,8 @@ def process_template_line(self, line):
         try:
             process_action = action_map[action]
         except KeyError:
-            raise DistutilsInternalError(
-                "this cannot happen: invalid action '{action!s}'".format(action=action),
-            )
+            msg = f"Invalid MANIFEST.in: unknown action {action!r} in {line!r}"
+            raise DistutilsInternalError(msg) from None
 
         # OK, now we know that the action is valid and we have the
         # right number of words on the line for that action -- so we
diff --git a/setuptools/command/sdist.py b/setuptools/command/sdist.py
index dc85161196..d455f44c5e 100644
--- a/setuptools/command/sdist.py
+++ b/setuptools/command/sdist.py
@@ -13,8 +13,7 @@
 def walk_revctrl(dirname=''):
     """Find all files under revision control"""
     for ep in metadata.entry_points(group='setuptools.file_finders'):
-        for item in ep.load()(dirname):
-            yield item
+        yield from ep.load()(dirname)
 
 
 class sdist(orig.sdist):
@@ -97,7 +96,7 @@ class NoValue:
             yield
         finally:
             if orig_val is not NoValue:
-                setattr(os, 'link', orig_val)
+                os.link = orig_val
 
     def add_defaults(self):
         super().add_defaults()
@@ -181,7 +180,7 @@ def _manifest_is_not_generated(self):
 
         with open(self.manifest, 'rb') as fp:
             first_line = fp.readline()
-        return first_line != '# file GENERATED by distutils, do NOT edit\n'.encode()
+        return first_line != b'# file GENERATED by distutils, do NOT edit\n'
 
     def read_manifest(self):
         """Read the manifest file (named by 'self.manifest') and use it to
diff --git a/setuptools/command/test.py b/setuptools/command/test.py
index 5fce6660c0..0a128f2a7a 100644
--- a/setuptools/command/test.py
+++ b/setuptools/command/test.py
@@ -132,7 +132,7 @@ def with_project_on_sys_path(self, func):
             func()
 
     @contextlib.contextmanager
-    def project_on_sys_path(self, include_dists=[]):
+    def project_on_sys_path(self, include_dists=()):
         self.run_command('egg_info')
 
         # Build extensions in-place
diff --git a/setuptools/config/_validate_pyproject/error_reporting.py b/setuptools/config/_validate_pyproject/error_reporting.py
index f78e4838fb..d44e290e36 100644
--- a/setuptools/config/_validate_pyproject/error_reporting.py
+++ b/setuptools/config/_validate_pyproject/error_reporting.py
@@ -24,7 +24,7 @@
     "must not be there",
 )
 
-_NEED_DETAILS = {"anyOf", "oneOf", "anyOf", "contains", "propertyNames", "not", "items"}
+_NEED_DETAILS = {"anyOf", "oneOf", "allOf", "contains", "propertyNames", "not", "items"}
 
 _CAMEL_CASE_SPLITTER = re.compile(r"\W+|([A-Z][^A-Z\W]*)")
 _IDENTIFIER = re.compile(r"^[\w_]+$", re.I)
diff --git a/setuptools/config/setupcfg.py b/setuptools/config/setupcfg.py
index 44a2876c06..a7f02714cb 100644
--- a/setuptools/config/setupcfg.py
+++ b/setuptools/config/setupcfg.py
@@ -283,8 +283,8 @@ def __setitem__(self, option_name, value):
 
         try:
             current_value = getattr(target_obj, option_name)
-        except AttributeError:
-            raise KeyError(option_name)
+        except AttributeError as e:
+            raise KeyError(option_name) from e
 
         if current_value:
             # Already inhabited. Skipping.
@@ -582,11 +582,11 @@ def _parse_version(self, value):
             # accidentally include newlines and other unintended content
             try:
                 Version(version)
-            except InvalidVersion:
+            except InvalidVersion as e:
                 raise OptionError(
                     f'Version loaded from {value} does not '
                     f'comply with PEP 440: {version}'
-                )
+                ) from e
 
             return version
 
diff --git a/setuptools/dist.py b/setuptools/dist.py
index c9c8c77515..0d35583dbc 100644
--- a/setuptools/dist.py
+++ b/setuptools/dist.py
@@ -912,11 +912,9 @@ def get_cmdline_options(self):
     def iter_distribution_names(self):
         """Yield all packages, modules, and extension names in distribution"""
 
-        for pkg in self.packages or ():
-            yield pkg
+        yield from self.packages or ()
 
-        for module in self.py_modules or ():
-            yield module
+        yield from self.py_modules or ()
 
         for ext in self.ext_modules or ():
             if isinstance(ext, tuple):
diff --git a/setuptools/glob.py b/setuptools/glob.py
index 8dbf34972d..a184c0b643 100644
--- a/setuptools/glob.py
+++ b/setuptools/glob.py
@@ -113,8 +113,7 @@ def glob0(dirname, basename):
 def glob2(dirname, pattern):
     assert _isrecursive(pattern)
     yield pattern[:0]
-    for x in _rlistdir(dirname):
-        yield x
+    yield from _rlistdir(dirname)
 
 
 # Recursively yields relative pathnames inside a literal directory.
@@ -126,7 +125,7 @@ def _rlistdir(dirname):
             dirname = os.curdir
     try:
         names = os.listdir(dirname)
-    except os.error:
+    except OSError:
         return
     for x in names:
         yield x
diff --git a/setuptools/monkey.py b/setuptools/monkey.py
index 2ff6c5fbfc..da0993506c 100644
--- a/setuptools/monkey.py
+++ b/setuptools/monkey.py
@@ -115,7 +115,7 @@ def patch_func(replacement, target_mod, func_name):
 
 
 def get_unpatched_function(candidate):
-    return getattr(candidate, 'unpatched')
+    return candidate.unpatched
 
 
 def patch_for_msvc_specialized_compiler():
diff --git a/setuptools/msvc.py b/setuptools/msvc.py
index be373d176e..aa69db5810 100644
--- a/setuptools/msvc.py
+++ b/setuptools/msvc.py
@@ -12,7 +12,6 @@
 """
 
 import json
-from io import open
 from os import listdir, pathsep
 from os.path import join, isfile, isdir, dirname
 from subprocess import CalledProcessError
diff --git a/setuptools/package_index.py b/setuptools/package_index.py
index 3cedd5105c..1e535bc747 100644
--- a/setuptools/package_index.py
+++ b/setuptools/package_index.py
@@ -112,15 +112,13 @@ def egg_info_for_url(url):
 def distros_for_url(url, metadata=None):
     """Yield egg or source distribution objects that might be found at a URL"""
     base, fragment = egg_info_for_url(url)
-    for dist in distros_for_location(url, base, metadata):
-        yield dist
+    yield from distros_for_location(url, base, metadata)
     if fragment:
         match = EGG_FRAGMENT.match(fragment)
         if match:
-            for dist in interpret_distro_name(
+            yield from interpret_distro_name(
                 url, match.group(1), metadata, precedence=CHECKOUT_DIST
-            ):
-                yield dist
+            )
 
 
 def distros_for_location(location, basename, metadata=None):
@@ -516,7 +514,7 @@ def obtain(self, requirement, installer=None):
             if dist in requirement:
                 return dist
             self.debug("%s does not match %s", requirement, dist)
-        return super(PackageIndex, self).obtain(requirement, installer)
+        return super().obtain(requirement, installer)
 
     def check_hash(self, checker, filename, tfp):
         """
diff --git a/setuptools/tests/config/test_setupcfg.py b/setuptools/tests/config/test_setupcfg.py
index d2bb1212dc..d235478f7e 100644
--- a/setuptools/tests/config/test_setupcfg.py
+++ b/setuptools/tests/config/test_setupcfg.py
@@ -957,17 +957,13 @@ class TestExternalSetters:
     # pbr or something else setting these values.
     def _fake_distribution_init(self, dist, attrs):
         saved_dist_init(dist, attrs)
-        # see self._DISTUTUILS_UNSUPPORTED_METADATA
-        setattr(dist.metadata, 'long_description_content_type', 'text/something')
+        # see self._DISTUTILS_UNSUPPORTED_METADATA
+        dist.metadata.long_description_content_type = 'text/something'
         # Test overwrite setup() args
-        setattr(
-            dist.metadata,
-            'project_urls',
-            {
-                'Link One': 'https://example.com/one/',
-                'Link Two': 'https://example.com/two/',
-            },
-        )
+        dist.metadata.project_urls = {
+            'Link One': 'https://example.com/one/',
+            'Link Two': 'https://example.com/two/',
+        }
         return None
 
     @patch.object(_Distribution, '__init__', autospec=True)
diff --git a/setuptools/tests/integration/helpers.py b/setuptools/tests/integration/helpers.py
index 824dfdfe1a..62076bdf7d 100644
--- a/setuptools/tests/integration/helpers.py
+++ b/setuptools/tests/integration/helpers.py
@@ -15,8 +15,7 @@
 def run(cmd, env=None):
     r = subprocess.run(
         cmd,
-        stdout=subprocess.PIPE,
-        stderr=subprocess.PIPE,
+        capture_output=True,
         universal_newlines=True,
         env={**os.environ, **(env or {})},
         # ^-- allow overwriting instead of discarding the current env
diff --git a/setuptools/tests/test_archive_util.py b/setuptools/tests/test_archive_util.py
index 7f9962440c..06d7f05aa0 100644
--- a/setuptools/tests/test_archive_util.py
+++ b/setuptools/tests/test_archive_util.py
@@ -1,5 +1,3 @@
-# coding: utf-8
-
 import tarfile
 import io
 
diff --git a/setuptools/tests/test_build_meta.py b/setuptools/tests/test_build_meta.py
index 429533229d..b912194805 100644
--- a/setuptools/tests/test_build_meta.py
+++ b/setuptools/tests/test_build_meta.py
@@ -30,9 +30,9 @@
 
 
 class BuildBackendBase:
-    def __init__(self, cwd='.', env={}, backend_name='setuptools.build_meta'):
+    def __init__(self, cwd='.', env=None, backend_name='setuptools.build_meta'):
         self.cwd = cwd
-        self.env = env
+        self.env = env or {}
         self.backend_name = backend_name
 
 
@@ -40,7 +40,7 @@ class BuildBackend(BuildBackendBase):
     """PEP 517 Build Backend"""
 
     def __init__(self, *args, **kwargs):
-        super(BuildBackend, self).__init__(*args, **kwargs)
+        super().__init__(*args, **kwargs)
         self.pool = futures.ProcessPoolExecutor(max_workers=1)
 
     def __getattr__(self, name):
@@ -73,7 +73,7 @@ def _kill(self, pid):
 
 class BuildBackendCaller(BuildBackendBase):
     def __init__(self, *args, **kwargs):
-        super(BuildBackendCaller, self).__init__(*args, **kwargs)
+        super().__init__(*args, **kwargs)
 
         (self.backend_name, _, self.backend_obj) = self.backend_name.partition(':')
 
diff --git a/setuptools/tests/test_dist.py b/setuptools/tests/test_dist.py
index 609932a9b3..99cd582501 100644
--- a/setuptools/tests/test_dist.py
+++ b/setuptools/tests/test_dist.py
@@ -116,7 +116,7 @@ def test_provides_extras_deterministic_order():
     # Invalid value type.
     (
         {
-            'hello': str('*.msg'),
+            'hello': '*.msg',
         },
         (
             "\"values of 'package_data' dict\" "
@@ -142,7 +142,7 @@ def test_check_package_data(package_data, expected_message):
         assert check_package_data(None, 'package_data', package_data) is None
     else:
         with pytest.raises(DistutilsSetupError, match=re.escape(expected_message)):
-            check_package_data(None, str('package_data'), package_data)
+            check_package_data(None, 'package_data', package_data)
 
 
 def test_check_specifier():
diff --git a/setuptools/tests/test_easy_install.py b/setuptools/tests/test_easy_install.py
index d0b95e09ea..ef85978ecb 100644
--- a/setuptools/tests/test_easy_install.py
+++ b/setuptools/tests/test_easy_install.py
@@ -53,7 +53,7 @@ class FakeDist:
     def get_entry_map(self, group):
         if group != 'console_scripts':
             return {}
-        return {str('name'): 'ep'}
+        return {'name': 'ep'}
 
     def as_requirement(self):
         return 'spec'
@@ -567,8 +567,8 @@ def test_setup_requires_honors_fetch_params(self, mock_index, monkeypatch):
         setup_requires, it should honor the fetch parameters (such as
         index-url, and find-links).
         """
-        monkeypatch.setenv(str('PIP_RETRIES'), str('0'))
-        monkeypatch.setenv(str('PIP_TIMEOUT'), str('0'))
+        monkeypatch.setenv('PIP_RETRIES', '0')
+        monkeypatch.setenv('PIP_TIMEOUT', '0')
         monkeypatch.setenv('PIP_NO_INDEX', 'false')
         with contexts.quiet():
             # create an sdist that has a build-time dependency.
@@ -653,7 +653,7 @@ def test_setup_requires_overrides_version_conflict(self, use_setup_cfg):
                 with contexts.quiet() as (stdout, stderr):
                     # Don't even need to install the package, just
                     # running the setup.py at all is sufficient
-                    run_setup(test_setup_py, [str('--name')])
+                    run_setup(test_setup_py, ['--name'])
 
                 lines = stdout.readlines()
                 assert len(lines) > 0
@@ -716,7 +716,7 @@ def test_setup_requires_override_nspkg(self, use_setup_cfg):
                     try:
                         # Don't even need to install the package, just
                         # running the setup.py at all is sufficient
-                        run_setup(test_setup_py, [str('--name')])
+                        run_setup(test_setup_py, ['--name'])
                     except pkg_resources.VersionConflict:
                         self.fail(
                             'Installing setup.py requirements '
@@ -766,16 +766,16 @@ def make_dependency_sdist(dist_path, distname, version):
                 )
                 test_setup_py = os.path.join(test_pkg, 'setup.py')
                 with contexts.quiet() as (stdout, stderr):
-                    run_setup(test_setup_py, [str('--version')])
+                    run_setup(test_setup_py, ['--version'])
                 lines = stdout.readlines()
                 assert len(lines) > 0
                 assert lines[-1].strip() == '42'
 
     def test_setup_requires_honors_pip_env(self, mock_index, monkeypatch):
-        monkeypatch.setenv(str('PIP_RETRIES'), str('0'))
-        monkeypatch.setenv(str('PIP_TIMEOUT'), str('0'))
+        monkeypatch.setenv('PIP_RETRIES', '0')
+        monkeypatch.setenv('PIP_TIMEOUT', '0')
         monkeypatch.setenv('PIP_NO_INDEX', 'false')
-        monkeypatch.setenv(str('PIP_INDEX_URL'), mock_index.url)
+        monkeypatch.setenv('PIP_INDEX_URL', mock_index.url)
         with contexts.save_pkg_resources_state():
             with contexts.tempdir() as temp_dir:
                 test_pkg = create_setup_requires_package(
@@ -796,14 +796,14 @@ def test_setup_requires_honors_pip_env(self, mock_index, monkeypatch):
                     )
                 test_setup_py = os.path.join(test_pkg, 'setup.py')
                 with pytest.raises(distutils.errors.DistutilsError):
-                    run_setup(test_setup_py, [str('--version')])
+                    run_setup(test_setup_py, ['--version'])
         assert len(mock_index.requests) == 1
         assert mock_index.requests[0].path == '/python-xlib/'
 
     def test_setup_requires_with_pep508_url(self, mock_index, monkeypatch):
-        monkeypatch.setenv(str('PIP_RETRIES'), str('0'))
-        monkeypatch.setenv(str('PIP_TIMEOUT'), str('0'))
-        monkeypatch.setenv(str('PIP_INDEX_URL'), mock_index.url)
+        monkeypatch.setenv('PIP_RETRIES', '0')
+        monkeypatch.setenv('PIP_TIMEOUT', '0')
+        monkeypatch.setenv('PIP_INDEX_URL', mock_index.url)
         with contexts.save_pkg_resources_state():
             with contexts.tempdir() as temp_dir:
                 dep_sdist = os.path.join(temp_dir, 'dep.tar.gz')
@@ -817,7 +817,7 @@ def test_setup_requires_with_pep508_url(self, mock_index, monkeypatch):
                     setup_attrs=dict(setup_requires='dependency @ %s' % dep_url),
                 )
                 test_setup_py = os.path.join(test_pkg, 'setup.py')
-                run_setup(test_setup_py, [str('--version')])
+                run_setup(test_setup_py, ['--version'])
         assert len(mock_index.requests) == 0
 
     def test_setup_requires_with_allow_hosts(self, mock_index):
@@ -843,15 +843,15 @@ def test_setup_requires_with_allow_hosts(self, mock_index):
                 path.build(files, prefix=temp_dir)
                 setup_py = str(pathlib.Path(temp_dir, 'test_pkg', 'setup.py'))
                 with pytest.raises(distutils.errors.DistutilsError):
-                    run_setup(setup_py, [str('--version')])
+                    run_setup(setup_py, ['--version'])
         assert len(mock_index.requests) == 0
 
     def test_setup_requires_with_python_requires(self, monkeypatch, tmpdir):
         """Check `python_requires` is honored."""
-        monkeypatch.setenv(str('PIP_RETRIES'), str('0'))
-        monkeypatch.setenv(str('PIP_TIMEOUT'), str('0'))
-        monkeypatch.setenv(str('PIP_NO_INDEX'), str('1'))
-        monkeypatch.setenv(str('PIP_VERBOSE'), str('1'))
+        monkeypatch.setenv('PIP_RETRIES', '0')
+        monkeypatch.setenv('PIP_TIMEOUT', '0')
+        monkeypatch.setenv('PIP_NO_INDEX', '1')
+        monkeypatch.setenv('PIP_VERBOSE', '1')
         dep_1_0_sdist = 'dep-1.0.tar.gz'
         dep_1_0_url = path_to_url(str(tmpdir / dep_1_0_sdist))
         dep_1_0_python_requires = '>=2.7'
@@ -898,7 +898,7 @@ def test_setup_requires_with_python_requires(self, monkeypatch, tmpdir):
                 setup_attrs=dict(setup_requires='dep', dependency_links=[index_url]),
             )
             test_setup_py = os.path.join(test_pkg, 'setup.py')
-            run_setup(test_setup_py, [str('--version')])
+            run_setup(test_setup_py, ['--version'])
         eggs = list(
             map(str, pkg_resources.find_distributions(os.path.join(test_pkg, '.eggs')))
         )
@@ -908,8 +908,8 @@ def test_setup_requires_with_python_requires(self, monkeypatch, tmpdir):
     def test_setup_requires_with_find_links_in_setup_cfg(
         self, monkeypatch, with_dependency_links_in_setup_py
     ):
-        monkeypatch.setenv(str('PIP_RETRIES'), str('0'))
-        monkeypatch.setenv(str('PIP_TIMEOUT'), str('0'))
+        monkeypatch.setenv('PIP_RETRIES', '0')
+        monkeypatch.setenv('PIP_TIMEOUT', '0')
         with contexts.save_pkg_resources_state():
             with contexts.tempdir() as temp_dir:
                 make_trivial_sdist(
@@ -946,7 +946,7 @@ def test_setup_requires_with_find_links_in_setup_cfg(
                             find_links=temp_dir,
                         )
                     )
-                run_setup(test_setup_py, [str('--version')])
+                run_setup(test_setup_py, ['--version'])
 
     def test_setup_requires_with_transitive_extra_dependency(self, monkeypatch):
         """
@@ -979,7 +979,7 @@ def test_setup_requires_with_transitive_extra_dependency(self, monkeypatch):
                     prefix=dep_pkg,
                 )
                 # "Install" dep.
-                run_setup(os.path.join(dep_pkg, 'setup.py'), [str('dist_info')])
+                run_setup(os.path.join(dep_pkg, 'setup.py'), ['dist_info'])
                 working_set.add_entry(dep_pkg)
                 # Create source tree for test package.
                 test_pkg = os.path.join(temp_dir, 'test_pkg')
@@ -995,11 +995,11 @@ def test_setup_requires_with_transitive_extra_dependency(self, monkeypatch):
                         )
                     )
                 # Check...
-                monkeypatch.setenv(str('PIP_FIND_LINKS'), str(temp_dir))
-                monkeypatch.setenv(str('PIP_NO_INDEX'), str('1'))
-                monkeypatch.setenv(str('PIP_RETRIES'), str('0'))
-                monkeypatch.setenv(str('PIP_TIMEOUT'), str('0'))
-                run_setup(test_setup_py, [str('--version')])
+                monkeypatch.setenv('PIP_FIND_LINKS', str(temp_dir))
+                monkeypatch.setenv('PIP_NO_INDEX', '1')
+                monkeypatch.setenv('PIP_RETRIES', '0')
+                monkeypatch.setenv('PIP_TIMEOUT', '0')
+                run_setup(test_setup_py, ['--version'])
 
     def test_setup_requires_with_distutils_command_dep(self, monkeypatch):
         """
@@ -1063,7 +1063,7 @@ class epcmd(build_py):
                     prefix=dep_pkg,
                 )
                 # "Install" dep.
-                run_setup(os.path.join(dep_pkg, 'setup.py'), [str('dist_info')])
+                run_setup(os.path.join(dep_pkg, 'setup.py'), ['dist_info'])
                 working_set.add_entry(dep_pkg)
                 # Create source tree for test package.
                 test_pkg = os.path.join(temp_dir, 'test_pkg')
@@ -1079,10 +1079,10 @@ class epcmd(build_py):
                         )
                     )
                 # Check...
-                monkeypatch.setenv(str('PIP_FIND_LINKS'), str(temp_dir))
-                monkeypatch.setenv(str('PIP_NO_INDEX'), str('1'))
-                monkeypatch.setenv(str('PIP_RETRIES'), str('0'))
-                monkeypatch.setenv(str('PIP_TIMEOUT'), str('0'))
+                monkeypatch.setenv('PIP_FIND_LINKS', str(temp_dir))
+                monkeypatch.setenv('PIP_NO_INDEX', '1')
+                monkeypatch.setenv('PIP_RETRIES', '0')
+                monkeypatch.setenv('PIP_TIMEOUT', '0')
                 run_setup(test_setup_py, ['epcmd'])
 
 
@@ -1195,7 +1195,7 @@ def create_setup_requires_package(
     version='0.1',
     make_package=make_trivial_sdist,
     setup_py_template=None,
-    setup_attrs={},
+    setup_attrs=None,
     use_setup_cfg=(),
 ):
     """Creates a source tree under path for a trivial test package that has a
@@ -1213,7 +1213,8 @@ def create_setup_requires_package(
         'setup_requires': ['%s==%s' % (distname, version)],
         'dependency_links': [os.path.abspath(path)],
     }
-    test_setup_attrs.update(setup_attrs)
+    if setup_attrs:
+        test_setup_attrs.update(setup_attrs)
 
     test_pkg = os.path.join(path, 'test_pkg')
     os.mkdir(test_pkg)
@@ -1286,7 +1287,7 @@ def test_get_script_header_non_ascii_exe(self):
         actual = ei.ScriptWriter.get_header(
             '#!/usr/bin/python', executable=self.non_ascii_exe
         )
-        expected = str('#!%s -x\n') % self.non_ascii_exe
+        expected = '#!%s -x\n' % self.non_ascii_exe
         assert actual == expected
 
     def test_get_script_header_exe_with_spaces(self):
diff --git a/setuptools/tests/test_integration.py b/setuptools/tests/test_integration.py
index e17ffc5d5c..1aa16172b5 100644
--- a/setuptools/tests/test_integration.py
+++ b/setuptools/tests/test_integration.py
@@ -64,7 +64,7 @@ def fin():
     monkeypatch.setattr('site.USER_BASE', user_base.strpath)
     monkeypatch.setattr('site.USER_SITE', user_site.strpath)
     monkeypatch.setattr('sys.path', sys.path + [install_dir.strpath])
-    monkeypatch.setenv(str('PYTHONPATH'), str(os.path.pathsep.join(sys.path)))
+    monkeypatch.setenv('PYTHONPATH', str(os.path.pathsep.join(sys.path)))
 
     # Set up the command for performing the installation.
     dist = Distribution()
diff --git a/setuptools/tests/test_manifest.py b/setuptools/tests/test_manifest.py
index 33d3250893..fbd21b1976 100644
--- a/setuptools/tests/test_manifest.py
+++ b/setuptools/tests/test_manifest.py
@@ -171,7 +171,7 @@ def teardown_method(self, method):
 
 class TestManifestTest(TempDirTestCase):
     def setup_method(self, method):
-        super(TestManifestTest, self).setup_method(method)
+        super().setup_method(method)
 
         f = open(os.path.join(self.temp_dir, 'setup.py'), 'w')
         f.write(SETUP_PY)
diff --git a/setuptools/tests/test_msvc14.py b/setuptools/tests/test_msvc14.py
index 619293cada..4b8344539f 100644
--- a/setuptools/tests/test_msvc14.py
+++ b/setuptools/tests/test_msvc14.py
@@ -57,7 +57,7 @@ def test_get_vc2017(self):
         # This function cannot be mocked, so pass it if we find VS 2017
         # and mark it skipped if we do not.
         version, path = _msvccompiler._msvc14_find_vc2017()
-        if os.environ.get('APPVEYOR_BUILD_WORKER_IMAGE', '') in ['Visual Studio 2017']:
+        if os.environ.get('APPVEYOR_BUILD_WORKER_IMAGE', '') == 'Visual Studio 2017':
             assert version
         if version:
             assert version >= 15
diff --git a/setuptools/tests/test_sdist.py b/setuptools/tests/test_sdist.py
index 0adec70f04..5d597709ed 100644
--- a/setuptools/tests/test_sdist.py
+++ b/setuptools/tests/test_sdist.py
@@ -658,7 +658,7 @@ def test_sdist_with_latin1_encoded_filename(self):
         else:
             # The Latin-1 filename should have been skipped
             filename = filename.decode('latin-1')
-            filename not in cmd.filelist.files
+            assert filename not in cmd.filelist.files
 
     _EXAMPLE_DIRECTIVES = {
         "setup.cfg - long_description and version": """
diff --git a/setuptools/tests/test_setuptools.py b/setuptools/tests/test_setuptools.py
index 1ca5523d20..0dc4769b93 100644
--- a/setuptools/tests/test_setuptools.py
+++ b/setuptools/tests/test_setuptools.py
@@ -61,13 +61,13 @@ def f1():
         assert dep.extract_constant(fc, 'q', -1) is None
 
         # constant assigned
-        dep.extract_constant(fc, 'x', -1) == "test"
+        assert dep.extract_constant(fc, 'x', -1) == "test"
 
         # expression assigned
-        dep.extract_constant(fc, 'y', -1) == -1
+        assert dep.extract_constant(fc, 'y', -1) == -1
 
         # recognized name, not assigned
-        dep.extract_constant(fc, 'z', -1) is None
+        assert dep.extract_constant(fc, 'z', -1) is None
 
     def testFindModule(self):
         with pytest.raises(ImportError):
diff --git a/tools/build_launchers.py b/tools/build_launchers.py
index 8d832b9c24..c673445365 100644
--- a/tools/build_launchers.py
+++ b/tools/build_launchers.py
@@ -118,8 +118,8 @@ def get_msbuild():
     ]
     try:
         return subprocess.check_output(cmd, encoding='utf-8', text=True).strip()
-    except subprocess.CalledProcessError:
-        raise SystemExit("Unable to find MSBuild; check Visual Studio install")
+    except subprocess.CalledProcessError as e:
+        raise SystemExit("Unable to find MSBuild; check Visual Studio install") from e
 
 
 def do_build(arena, platform, target):