diff --git a/doc/conf.py b/doc/conf.py
index 58cbfe708..d32ee47ae 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -48,7 +48,7 @@ epub_fix_images = False
 epub_max_image_width = 0
 epub_show_urls = 'inline'
 epub_use_index = False
-epub_guide = (('toc', 'contents.xhtml', u'Table of Contents'),)
+epub_guide = (('toc', 'contents.xhtml', 'Table of Contents'),)
 epub_description = 'Sphinx documentation generator system manual'
 
 latex_documents = [('contents', 'sphinx.tex', 'Sphinx Documentation',
diff --git a/sphinx/builders/changes.py b/sphinx/builders/changes.py
index f6bfe1b64..3b169e493 100644
--- a/sphinx/builders/changes.py
+++ b/sphinx/builders/changes.py
@@ -148,8 +148,8 @@ class ChangesBuilder(Builder):
                     'text': text
                 }
                 f.write(self.templates.render('changes/rstsource.html', ctx))
-        themectx = dict(('theme_' + key, val) for (key, val) in
-                        self.theme.get_options({}).items())
+        themectx = {'theme_' + key: val for (key, val) in
+                    self.theme.get_options({}).items()}
         copy_asset_file(path.join(package_dir, 'themes', 'default', 'static', 'default.css_t'),
                         self.outdir, context=themectx, renderer=self.templates)
         copy_asset_file(path.join(package_dir, 'themes', 'basic', 'static', 'basic.css'),
diff --git a/sphinx/builders/html.py b/sphinx/builders/html.py
index 2c5ebcd4d..3f167d0d3 100644
--- a/sphinx/builders/html.py
+++ b/sphinx/builders/html.py
@@ -187,7 +187,7 @@ class BuildInfo:
         self.tags_hash = ''
 
         if config:
-            values = dict((c.name, c.value) for c in config.filter(config_categories))
+            values = {c.name: c.value for c in config.filter(config_categories)}
             self.config_hash = get_stable_hash(values)
 
         if tags:
diff --git a/sphinx/cmd/quickstart.py b/sphinx/cmd/quickstart.py
index c8b1b4fdd..dfc096de5 100644
--- a/sphinx/cmd/quickstart.py
+++ b/sphinx/cmd/quickstart.py
@@ -349,8 +349,7 @@ document is a custom template, you can also set this to another filename.'''))
                 d['extensions'].append('sphinx.ext.%s' % name)
 
         # Handle conflicting options
-        if set(['sphinx.ext.imgmath', 'sphinx.ext.mathjax']).issubset(
-                d['extensions']):
+        if {'sphinx.ext.imgmath', 'sphinx.ext.mathjax'}.issubset(d['extensions']):
             print(__('Note: imgmath and mathjax cannot be enabled at the same '
                      'time. imgmath has been deselected.'))
             d['extensions'].remove('sphinx.ext.imgmath')
@@ -469,7 +468,7 @@ def valid_dir(d):
     if not path.isdir(dir):
         return False
 
-    if set(['Makefile', 'make.bat']) & set(os.listdir(dir)):
+    if {'Makefile', 'make.bat'} & set(os.listdir(dir)):
         return False
 
     if d['sep']:
@@ -590,7 +589,7 @@ def main(argv=sys.argv[1:]):
 
     d = vars(args)
     # delete None or False value
-    d = dict((k, v) for k, v in d.items() if v is not None)
+    d = {k: v for k, v in d.items() if v is not None}
 
     # handle use of CSV-style extension values
     d.setdefault('extensions', [])
@@ -601,12 +600,12 @@ def main(argv=sys.argv[1:]):
 
     try:
         if 'quiet' in d:
-            if not set(['project', 'author']).issubset(d):
+            if not {'project', 'author'}.issubset(d):
                 print(__('''"quiet" is specified, but any of "project" or \
 "author" is not specified.'''))
                 return 1
 
-        if set(['quiet', 'project', 'author']).issubset(d):
+        if {'quiet', 'project', 'author'}.issubset(d):
             # quiet mode with all required params satisfied, use default
             d.setdefault('version', '')
             d.setdefault('release', d['version'])
diff --git a/sphinx/deprecation.py b/sphinx/deprecation.py
index e10ec8b32..6cdd22ec1 100644
--- a/sphinx/deprecation.py
+++ b/sphinx/deprecation.py
@@ -37,7 +37,7 @@ def deprecated_alias(modname, objects, warning):
     sys.modules[modname] = _ModuleWrapper(module, modname, objects, warning)  # type: ignore
 
 
-class _ModuleWrapper(object):
+class _ModuleWrapper:
     def __init__(self, module, modname, objects, warning):
         # type: (Any, str, Dict, Type[Warning]) -> None
         self._module = module
diff --git a/sphinx/domains/c.py b/sphinx/domains/c.py
index 46d92f5e1..ec311cfc7 100644
--- a/sphinx/domains/c.py
+++ b/sphinx/domains/c.py
@@ -72,12 +72,12 @@ class CObject(ObjectDescription):
 
     # These C types aren't described anywhere, so don't try to create
     # a cross-reference to them
-    stopwords = set((
+    stopwords = {
         'const', 'void', 'char', 'wchar_t', 'int', 'short',
         'long', 'float', 'double', 'unsigned', 'signed', 'FILE',
         'clock_t', 'time_t', 'ptrdiff_t', 'size_t', 'ssize_t',
         'struct', '_Bool',
-    ))
+    }
 
     def _parse_type(self, node, ctype):
         # type: (nodes.Element, str) -> None
diff --git a/sphinx/ext/apidoc.py b/sphinx/ext/apidoc.py
index 94f07d91f..2d9a771d1 100644
--- a/sphinx/ext/apidoc.py
+++ b/sphinx/ext/apidoc.py
@@ -45,7 +45,7 @@ else:
     ]
 
 INITPY = '__init__.py'
-PY_SUFFIXES = set(['.py', '.pyx'])
+PY_SUFFIXES = {'.py', '.pyx'}
 
 
 def makename(package, module):
diff --git a/sphinx/ext/autodoc/__init__.py b/sphinx/ext/autodoc/__init__.py
index f4b0c368f..5c94d611d 100644
--- a/sphinx/ext/autodoc/__init__.py
+++ b/sphinx/ext/autodoc/__init__.py
@@ -80,7 +80,7 @@ def members_set_option(arg):
     """Used to convert the :members: option to auto directives."""
     if arg is None:
         return ALL
-    return set(x.strip() for x in arg.split(','))
+    return {x.strip() for x in arg.split(',')}
 
 
 SUPPRESS = object()
diff --git a/sphinx/ext/ifconfig.py b/sphinx/ext/ifconfig.py
index 4fd5fa391..930ed9954 100644
--- a/sphinx/ext/ifconfig.py
+++ b/sphinx/ext/ifconfig.py
@@ -56,7 +56,7 @@ class IfConfig(SphinxDirective):
 
 def process_ifconfig_nodes(app, doctree, docname):
     # type: (Sphinx, nodes.document, str) -> None
-    ns = dict((confval.name, confval.value) for confval in app.config)
+    ns = {confval.name: confval.value for confval in app.config}
     ns.update(app.config.__dict__.copy())
     ns['builder'] = app.builder.name
     for node in doctree.traverse(ifconfig):
diff --git a/sphinx/ext/intersphinx.py b/sphinx/ext/intersphinx.py
index 9c26d8c56..6b9bc3825 100644
--- a/sphinx/ext/intersphinx.py
+++ b/sphinx/ext/intersphinx.py
@@ -150,9 +150,9 @@ def _get_safe_url(url):
     else:
         frags = list(parts)
         if parts.port:
-            frags[1] = '{0}@{1}:{2}'.format(parts.username, parts.hostname, parts.port)
+            frags[1] = '{}@{}:{}'.format(parts.username, parts.hostname, parts.port)
         else:
-            frags[1] = '{0}@{1}'.format(parts.username, parts.hostname)
+            frags[1] = '{}@{}'.format(parts.username, parts.hostname)
 
         return urlunsplit(frags)
 
diff --git a/sphinx/io.py b/sphinx/io.py
index 368f661d5..d3c4b2183 100644
--- a/sphinx/io.py
+++ b/sphinx/io.py
@@ -202,7 +202,7 @@ class SphinxFileInput(FileInput):
     def __init__(self, *args, **kwargs):
         # type: (Any, Any) -> None
         kwargs['error_handler'] = 'sphinx'
-        super(SphinxFileInput, self).__init__(*args, **kwargs)
+        super().__init__(*args, **kwargs)
 
 
 class SphinxRSTFileInput(SphinxBaseFileInput):
diff --git a/sphinx/project.py b/sphinx/project.py
index c7094503f..8e2e7330a 100644
--- a/sphinx/project.py
+++ b/sphinx/project.py
@@ -24,7 +24,7 @@ logger = logging.getLogger(__name__)
 EXCLUDE_PATHS = ['**/_sources', '.#*', '**/.#*', '*.lproj/**']
 
 
-class Project(object):
+class Project:
     """A project is source code set of Sphinx document."""
 
     def __init__(self, srcdir, source_suffix):
diff --git a/sphinx/search/__init__.py b/sphinx/search/__init__.py
index dd30b5045..868b0e489 100644
--- a/sphinx/search/__init__.py
+++ b/sphinx/search/__init__.py
@@ -310,9 +310,9 @@ class IndexBuilder:
             rv = {}
             for k, v in mapping.items():
                 if isinstance(v, int):
-                    rv[k] = set([index2fn[v]])
+                    rv[k] = {index2fn[v]}
                 else:
-                    rv[k] = set(index2fn[i] for i in v)
+                    rv[k] = {index2fn[i] for i in v}
             return rv
 
         self._mapping = load_terms(frozen['terms'])
@@ -381,12 +381,11 @@ class IndexBuilder:
         """Create a usable data structure for serializing."""
         docnames, titles = zip(*sorted(self._titles.items()))
         filenames = [self._filenames.get(docname) for docname in docnames]
-        fn2index = dict((f, i) for (i, f) in enumerate(docnames))
+        fn2index = {f: i for (i, f) in enumerate(docnames)}
         terms, title_terms = self.get_terms(fn2index)
 
         objects = self.get_objects(fn2index)  # populates _objtypes
-        objtypes = dict((v, k[0] + ':' + k[1])
-                        for (k, v) in self._objtypes.items())
+        objtypes = {v: k[0] + ':' + k[1] for (k, v) in self._objtypes.items()}
         objnames = self._objnames
         return dict(docnames=docnames, filenames=filenames, titles=titles, terms=terms,
                     objects=objects, objtypes=objtypes, objnames=objnames,
diff --git a/sphinx/search/ja.py b/sphinx/search/ja.py
index 814296f79..0c11af74d 100644
--- a/sphinx/search/ja.py
+++ b/sphinx/search/ja.py
@@ -155,14 +155,14 @@ class JanomeSplitter(BaseSplitter):
 
 
 class DefaultSplitter(BaseSplitter):
-    patterns_ = dict([(re.compile(pattern), value) for pattern, value in {
+    patterns_ = {re.compile(pattern): value for pattern, value in {
         '[一二三四五六七八九十百千万億兆]': 'M',
         '[一-龠々〆ヵヶ]': 'H',
         '[ぁ-ん]': 'I',
         '[ァ-ヴーｱ-ﾝﾞｰ]': 'K',
         '[a-zA-Zａ-ｚＡ-Ｚ]': 'A',
         '[0-9０-９]': 'N',
-    }.items()])
+    }.items()}
     BIAS__ = -332
     BC1__ = {'HH': 6, 'II': 2461, 'KH': 406, 'OH': -1378}
     BC2__ = {'AA': -3267, 'AI': 2744, 'AN': -878, 'HH': -4070, 'HM': -1711,
diff --git a/sphinx/testing/util.py b/sphinx/testing/util.py
index fbd05c5d1..7b73059e9 100644
--- a/sphinx/testing/util.py
+++ b/sphinx/testing/util.py
@@ -133,8 +133,8 @@ class SphinxTestApp(application.Sphinx):
         self._saved_directives = directives._directives.copy()  # type: ignore
         self._saved_roles = roles._roles.copy()  # type: ignore
 
-        self._saved_nodeclasses = set(v for v in dir(nodes.GenericNodeVisitor)
-                                      if v.startswith('visit_'))
+        self._saved_nodeclasses = {v for v in dir(nodes.GenericNodeVisitor)
+                                   if v.startswith('visit_')}
 
         try:
             super().__init__(srcdir, confdir, outdir, doctreedir,
diff --git a/sphinx/transforms/__init__.py b/sphinx/transforms/__init__.py
index 6f513377b..d489db334 100644
--- a/sphinx/transforms/__init__.py
+++ b/sphinx/transforms/__init__.py
@@ -36,11 +36,11 @@ if False:
 
 logger = logging.getLogger(__name__)
 
-default_substitutions = set([
+default_substitutions = {
     'version',
     'release',
     'today',
-])
+}
 
 
 class SphinxTransform(Transform):
diff --git a/sphinx/util/__init__.py b/sphinx/util/__init__.py
index def90125c..b266b955d 100644
--- a/sphinx/util/__init__.py
+++ b/sphinx/util/__init__.py
@@ -138,7 +138,7 @@ class FilenameUniqDict(dict):
         while uniquename in self._existing:
             i += 1
             uniquename = '%s%s%s' % (base, i, ext)
-        self[newfile] = (set([docname]), uniquename)
+        self[newfile] = ({docname}, uniquename)
         self._existing.add(uniquename)
         return uniquename
 
diff --git a/tests/test_application.py b/tests/test_application.py
index 87ee72f63..6bc454311 100644
--- a/tests/test_application.py
+++ b/tests/test_application.py
@@ -61,7 +61,7 @@ def test_extension_in_blacklist(app, status, warning):
 @pytest.mark.filterwarnings('ignore:The config variable "source_parsers"')
 @pytest.mark.filterwarnings('ignore:app.add_source_parser\\(\\) does not support suffix')
 def test_add_source_parser(app, status, warning):
-    assert set(app.config.source_suffix) == set(['.rst', '.md', '.test'])
+    assert set(app.config.source_suffix) == {'.rst', '.md', '.test'}
 
     # .rst; only in :confval:`source_suffix`
     assert '.rst' not in app.registry.get_source_parsers()
diff --git a/tests/test_builder.py b/tests/test_builder.py
index 35197a8ef..fa64f0c1f 100644
--- a/tests/test_builder.py
+++ b/tests/test_builder.py
@@ -28,7 +28,7 @@ def test_incremental_reading(app):
     # second reading
     updated = app.builder.read()
 
-    assert set(updated) == set(['index', 'new'])
+    assert set(updated) == {'index', 'new'}
     assert 'autodoc' not in app.env.all_docs
     assert 'autodoc' not in app.env.found_docs
 
@@ -44,4 +44,4 @@ def test_incremental_reading_for_missing_files(app):
 
     # "index" is listed up to updated because it contains references
     # to nonexisting downloadable or image files
-    assert set(updated) == set(['index'])
+    assert set(updated) == {'index'}
diff --git a/tests/test_catalogs.py b/tests/test_catalogs.py
index 14fca84d5..1355280e3 100644
--- a/tests/test_catalogs.py
+++ b/tests/test_catalogs.py
@@ -42,10 +42,10 @@ def test_compile_all_catalogs(app, status, warning):
 
     locale_dir = app.srcdir / 'locale'
     catalog_dir = locale_dir / app.config.language / 'LC_MESSAGES'
-    expect = set([
+    expect = {
         x.replace('.po', '.mo')
         for x in find_files(catalog_dir, '.po')
-    ])
+    }
     actual = set(find_files(catalog_dir, '.mo'))
     assert actual  # not empty
     assert actual == expect
@@ -66,7 +66,7 @@ def test_compile_specific_catalogs(app, status, warning):
     actual_on_boot = get_actual()  # sphinx.mo might be included
     app.builder.compile_specific_catalogs([app.srcdir / 'admonitions.txt'])
     actual = get_actual() - actual_on_boot
-    assert actual == set(['admonitions.mo'])
+    assert actual == {'admonitions.mo'}
 
 
 @pytest.mark.usefixtures('setup_test')
@@ -79,10 +79,10 @@ def test_compile_update_catalogs(app, status, warning):
 
     locale_dir = app.srcdir / 'locale'
     catalog_dir = locale_dir / app.config.language / 'LC_MESSAGES'
-    expect = set([
+    expect = {
         x.replace('.po', '.mo')
         for x in find_files(catalog_dir, '.po')
-    ])
+    }
     actual = set(find_files(catalog_dir, '.mo'))
     assert actual  # not empty
     assert actual == expect
diff --git a/tests/test_environment.py b/tests/test_environment.py
index df0aa20b0..15562536f 100644
--- a/tests/test_environment.py
+++ b/tests/test_environment.py
@@ -25,21 +25,20 @@ def test_images(app):
     htmlbuilder.imgpath = 'dummy'
     htmlbuilder.post_process_images(tree)
     assert set(htmlbuilder.images.keys()) == \
-        set(['subdir/img.png', 'img.png', 'subdir/simg.png', 'svgimg.svg',
-             'img.foo.png'])
+        {'subdir/img.png', 'img.png', 'subdir/simg.png', 'svgimg.svg', 'img.foo.png'}
     assert set(htmlbuilder.images.values()) == \
-        set(['img.png', 'img1.png', 'simg.png', 'svgimg.svg', 'img.foo.png'])
+        {'img.png', 'img1.png', 'simg.png', 'svgimg.svg', 'img.foo.png'}
 
     latexbuilder = LaTeXBuilder(app)
     latexbuilder.set_environment(app.env)
     latexbuilder.init()
     latexbuilder.post_process_images(tree)
     assert set(latexbuilder.images.keys()) == \
-        set(['subdir/img.png', 'subdir/simg.png', 'img.png', 'img.pdf',
-             'svgimg.pdf', 'img.foo.png'])
+        {'subdir/img.png', 'subdir/simg.png', 'img.png', 'img.pdf',
+         'svgimg.pdf', 'img.foo.png'}
     assert set(latexbuilder.images.values()) == \
-        set(['img.pdf', 'img.png', 'img1.png', 'simg.png',
-             'svgimg.pdf', 'img.foo.png'])
+        {'img.pdf', 'img.png', 'img1.png', 'simg.png',
+         'svgimg.pdf', 'img.foo.png'}
 
 
 @pytest.mark.sphinx('dummy')
diff --git a/tests/test_environment_toctree.py b/tests/test_environment_toctree.py
index c490dcedf..9d880d92c 100644
--- a/tests/test_environment_toctree.py
+++ b/tests/test_environment_toctree.py
@@ -75,11 +75,11 @@ def test_process_doc(app):
     # other collections
     assert app.env.toc_num_entries['index'] == 6
     assert app.env.toctree_includes['index'] == ['foo', 'bar', 'baz']
-    assert app.env.files_to_rebuild['foo'] == set(['index'])
-    assert app.env.files_to_rebuild['bar'] == set(['index'])
-    assert app.env.files_to_rebuild['baz'] == set(['index'])
+    assert app.env.files_to_rebuild['foo'] == {'index'}
+    assert app.env.files_to_rebuild['bar'] == {'index'}
+    assert app.env.files_to_rebuild['baz'] == {'index'}
     assert app.env.glob_toctrees == set()
-    assert app.env.numbered_toctrees == set(['index'])
+    assert app.env.numbered_toctrees == {'index'}
 
     # qux has no section title
     assert len(app.env.tocs['qux']) == 0
diff --git a/tests/test_ext_coverage.py b/tests/test_ext_coverage.py
index d02d65feb..73181909d 100644
--- a/tests/test_ext_coverage.py
+++ b/tests/test_ext_coverage.py
@@ -37,7 +37,7 @@ def test_build(app, status, warning):
     undoc_py, undoc_c = pickle.loads((app.outdir / 'undoc.pickle').bytes())
     assert len(undoc_c) == 1
     # the key is the full path to the header file, which isn't testable
-    assert list(undoc_c.values())[0] == set([('function', 'Py_SphinxTest')])
+    assert list(undoc_c.values())[0] == {('function', 'Py_SphinxTest')}
 
     assert 'autodoc_target' in undoc_py
     assert 'funcs' in undoc_py['autodoc_target']
diff --git a/tests/test_ext_inheritance_diagram.py b/tests/test_ext_inheritance_diagram.py
index 9e5d3e60f..03b5bb689 100644
--- a/tests/test_ext_inheritance_diagram.py
+++ b/tests/test_ext_inheritance_diagram.py
@@ -121,7 +121,7 @@ def test_import_classes(rootdir):
 
         # all of classes in the module
         classes = import_classes('sphinx.application', None)
-        assert set(classes) == set([Sphinx, TemplateBridge])
+        assert set(classes) == {Sphinx, TemplateBridge}
 
         # specified class in the module
         classes = import_classes('sphinx.application.Sphinx', None)
diff --git a/tests/test_ext_napoleon_docstring.py b/tests/test_ext_napoleon_docstring.py
index fa75062b3..86ded7d89 100644
--- a/tests/test_ext_napoleon_docstring.py
+++ b/tests/test_ext_napoleon_docstring.py
@@ -36,7 +36,7 @@ class NamedtupleSubclass(namedtuple('NamedtupleSubclass', ('attr1', 'attr2'))):
     __slots__ = ()
 
     def __new__(cls, attr1, attr2=None):
-        return super(NamedtupleSubclass, cls).__new__(cls, attr1, attr2)
+        return super().__new__(cls, attr1, attr2)
 
 
 class BaseDocstringTest(TestCase):
diff --git a/tests/test_ext_todo.py b/tests/test_ext_todo.py
index 2ce7ac95e..3fca33f6f 100644
--- a/tests/test_ext_todo.py
+++ b/tests/test_ext_todo.py
@@ -54,9 +54,9 @@ def test_todo(app, status, warning):
 
     # check handled event
     assert len(todos) == 3
-    assert set(todo[1].astext() for todo in todos) == {'todo in foo',
-                                                       'todo in bar',
-                                                       'todo in param field'}
+    assert {todo[1].astext() for todo in todos} == {'todo in foo',
+                                                    'todo in bar',
+                                                    'todo in param field'}
 
 
 @pytest.mark.sphinx('html', testroot='ext-todo', freshenv=True,
@@ -92,9 +92,9 @@ def test_todo_not_included(app, status, warning):
 
     # check handled event
     assert len(todos) == 3
-    assert set(todo[1].astext() for todo in todos) == {'todo in foo',
-                                                       'todo in bar',
-                                                       'todo in param field'}
+    assert {todo[1].astext() for todo in todos} == {'todo in foo',
+                                                    'todo in bar',
+                                                    'todo in param field'}
 
 
 @pytest.mark.sphinx('latex', testroot='ext-todo', freshenv=True,
diff --git a/tests/test_intl.py b/tests/test_intl.py
index 367409fd9..35e8f6909 100644
--- a/tests/test_intl.py
+++ b/tests/test_intl.py
@@ -829,8 +829,7 @@ def test_xml_footnote_backlinks(app):
 
     para0 = secs[0].findall('paragraph')
     refs0 = para0[0].findall('footnote_reference')
-    refid2id = dict([
-        (r.attrib.get('refid'), r.attrib.get('ids')) for r in refs0])
+    refid2id = {r.attrib.get('refid'): r.attrib.get('ids') for r in refs0}
 
     footnote0 = secs[0].findall('footnote')
     for footnote in footnote0:
diff --git a/tests/test_util_i18n.py b/tests/test_util_i18n.py
index b25e29575..a0d0d5577 100644
--- a/tests/test_util_i18n.py
+++ b/tests/test_util_i18n.py
@@ -70,13 +70,13 @@ def test_get_catalogs_for_xx(tempdir):
     (tempdir / 'loc1' / 'xx' / 'LC_ALL' / 'test7.po').write_text('#')
 
     catalogs = i18n.find_catalog_source_files([tempdir / 'loc1'], 'xx', force_all=False)
-    domains = set(c.domain for c in catalogs)
-    assert domains == set([
+    domains = {c.domain for c in catalogs}
+    assert domains == {
         'test1',
         'test2',
         'sub/test4',
         'sub/test5',
-    ])
+    }
 
 
 def test_get_catalogs_for_en(tempdir):
@@ -86,8 +86,8 @@ def test_get_catalogs_for_en(tempdir):
     (tempdir / 'loc1' / 'en' / 'LC_MESSAGES' / 'en_dom.po').write_text('#')
 
     catalogs = i18n.find_catalog_source_files([tempdir / 'loc1'], 'en', force_all=False)
-    domains = set(c.domain for c in catalogs)
-    assert domains == set(['en_dom'])
+    domains = {c.domain for c in catalogs}
+    assert domains == {'en_dom'}
 
 
 def test_get_catalogs_with_non_existent_locale(tempdir):
@@ -121,13 +121,13 @@ def test_get_catalogs_for_xx_without_outdated(tempdir):
     assert not catalogs
 
     catalogs = i18n.find_catalog_source_files([tempdir / 'loc1'], 'xx', force_all=True)
-    domains = set(c.domain for c in catalogs)
-    assert domains == set([
+    domains = {c.domain for c in catalogs}
+    assert domains == {
         'test1',
         'test2',
         'sub/test4',
         'sub/test5',
-    ])
+    }
 
 
 def test_get_catalogs_from_multiple_locale_dirs(tempdir):
@@ -152,8 +152,8 @@ def test_get_catalogs_with_compact(tempdir):
     (tempdir / 'loc1' / 'xx' / 'LC_MESSAGES' / 'sub' / 'test4.po').write_text('#')
 
     catalogs = i18n.find_catalog_source_files([tempdir / 'loc1'], 'xx', gettext_compact=True)
-    domains = set(c.domain for c in catalogs)
-    assert domains == set(['test1', 'test2', 'sub/test3', 'sub/test4'])
+    domains = {c.domain for c in catalogs}
+    assert domains == {'test1', 'test2', 'sub/test3', 'sub/test4'}
 
 
 def test_get_catalogs_excluded(tempdir):
@@ -163,8 +163,8 @@ def test_get_catalogs_excluded(tempdir):
 
     catalogs = i18n.find_catalog_source_files(
         [tempdir / 'loc1'], 'en', force_all=False, excluded=lambda path: '.git' in path)
-    domains = set(c.domain for c in catalogs)
-    assert domains == set(['en_dom'])
+    domains = {c.domain for c in catalogs}
+    assert domains == {'en_dom'}
 
 
 def test_format_date():
diff --git a/tests/test_util_inspect.py b/tests/test_util_inspect.py
index 6cb2a4b1b..ba2bb7501 100644
--- a/tests/test_util_inspect.py
+++ b/tests/test_util_inspect.py
@@ -352,7 +352,7 @@ def test_set_sorting():
 
 
 def test_set_sorting_fallback():
-    set_ = set((None, 1))
+    set_ = {None, 1}
     description = inspect.object_description(set_)
     assert description in ("{1, None}", "{None, 1}")
 
diff --git a/utils/jssplitter_generator.py b/utils/jssplitter_generator.py
index 255bc0a98..360ce7d15 100644
--- a/utils/jssplitter_generator.py
+++ b/utils/jssplitter_generator.py
@@ -79,7 +79,7 @@ function splitQuery(query) {
 }
 ''' % (fold(singles, ','), fold(ranges, '],'))
 
-js_test_src = u'''
+js_test_src = '''
 // This is regression test for https://github.com/sphinx-doc/sphinx/issues/3150
 // generated by compat_regexp_generator.py
 // it needs node.js for testing