style: use Black everywhere (#2594)

* style: use Black everywhere

* style: minor touchup from review

.pre-commit-config.yaml

@@ -36,8 +36,7 @@ repos:
   - id: black
     # By default, this ignores pyi files, though black supports them
     types: [text]
-    # Not all Python files are Blacked, yet
-    files: ^(setup.py|pybind11|tests/extra|tools).*\.pyi?$
+    files: \.pyi?$
 
 # Changes tabs to spaces
 - repo: https://github.com/Lucas-C/pre-commit-hooks

docs/benchmark.py

@@ -14,7 +14,7 @@ def generate_dummy_code_pybind11(nclasses=10):
 
     for cl in range(nclasses):
         decl += "class cl%03i;\n" % cl
-    decl += '\n'
+    decl += "\n"
 
     for cl in range(nclasses):
         decl += "class cl%03i {\n" % cl
@@ -22,18 +22,17 @@ def generate_dummy_code_pybind11(nclasses=10):
         bindings += '    py::class_<cl%03i>(m, "cl%03i")\n' % (cl, cl)
         for fn in range(nfns):
             ret = random.randint(0, nclasses - 1)
-            params  = [random.randint(0, nclasses - 1) for i in range(nargs)]
+            params = [random.randint(0, nclasses - 1) for i in range(nargs)]
             decl += "    cl%03i *fn_%03i(" % (ret, fn)
             decl += ", ".join("cl%03i *" % p for p in params)
             decl += ");\n"
-            bindings += '        .def("fn_%03i", &cl%03i::fn_%03i)\n' % \
-                (fn, cl, fn)
+            bindings += '        .def("fn_%03i", &cl%03i::fn_%03i)\n' % (fn, cl, fn)
         decl += "};\n\n"
-        bindings += '        ;\n'
+        bindings += "        ;\n"
 
     result = "#include <pybind11/pybind11.h>\n\n"
     result += "namespace py = pybind11;\n\n"
-    result += decl + '\n'
+    result += decl + "\n"
     result += "PYBIND11_MODULE(example, m) {\n"
     result += bindings
     result += "}"
@@ -46,7 +45,7 @@ def generate_dummy_code_boost(nclasses=10):
 
     for cl in range(nclasses):
         decl += "class cl%03i;\n" % cl
-    decl += '\n'
+    decl += "\n"
 
     for cl in range(nclasses):
         decl += "class cl%03i {\n" % cl
@@ -54,18 +53,20 @@ def generate_dummy_code_boost(nclasses=10):
         bindings += '    py::class_<cl%03i>("cl%03i")\n' % (cl, cl)
         for fn in range(nfns):
             ret = random.randint(0, nclasses - 1)
-            params  = [random.randint(0, nclasses - 1) for i in range(nargs)]
+            params = [random.randint(0, nclasses - 1) for i in range(nargs)]
             decl += "    cl%03i *fn_%03i(" % (ret, fn)
             decl += ", ".join("cl%03i *" % p for p in params)
             decl += ");\n"
-            bindings += '        .def("fn_%03i", &cl%03i::fn_%03i, py::return_value_policy<py::manage_new_object>())\n' % \
-                (fn, cl, fn)
+            bindings += (
+                '        .def("fn_%03i", &cl%03i::fn_%03i, py::return_value_policy<py::manage_new_object>())\n'
+                % (fn, cl, fn)
+            )
         decl += "};\n\n"
-        bindings += '        ;\n'
+        bindings += "        ;\n"
 
     result = "#include <boost/python.hpp>\n\n"
     result += "namespace py = boost::python;\n\n"
-    result += decl + '\n'
+    result += decl + "\n"
     result += "BOOST_PYTHON_MODULE(example) {\n"
     result += bindings
     result += "}"
@@ -73,17 +74,19 @@ def generate_dummy_code_boost(nclasses=10):
 
 
 for codegen in [generate_dummy_code_pybind11, generate_dummy_code_boost]:
-    print ("{")
+    print("{")
     for i in range(0, 10):
         nclasses = 2 ** i
         with open("test.cpp", "w") as f:
             f.write(codegen(nclasses))
         n1 = dt.datetime.now()
-        os.system("g++ -Os -shared -rdynamic -undefined dynamic_lookup "
+        os.system(
+            "g++ -Os -shared -rdynamic -undefined dynamic_lookup "
             "-fvisibility=hidden -std=c++14 test.cpp -I include "
-            "-I /System/Library/Frameworks/Python.framework/Headers -o test.so")
+            "-I /System/Library/Frameworks/Python.framework/Headers -o test.so"
+        )
         n2 = dt.datetime.now()
         elapsed = (n2 - n1).total_seconds()
-        size = os.stat('test.so').st_size
+        size = os.stat("test.so").st_size
         print("   {%i, %f, %i}," % (nclasses * nfns, elapsed, size))
-    print ("}")
+    print("}")

docs/conf.py

@@ -21,40 +21,44 @@ import subprocess
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
-#sys.path.insert(0, os.path.abspath('.'))
+# sys.path.insert(0, os.path.abspath('.'))
 
 # -- General configuration ------------------------------------------------
 
 # If your documentation needs a minimal Sphinx version, state it here.
-#needs_sphinx = '1.0'
+# needs_sphinx = '1.0'
 
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = ['breathe', 'sphinxcontrib.rsvgconverter', 'sphinxcontrib.moderncmakedomain']
+extensions = [
+    "breathe",
+    "sphinxcontrib.rsvgconverter",
+    "sphinxcontrib.moderncmakedomain",
+]
 
-breathe_projects = {'pybind11': '.build/doxygenxml/'}
-breathe_default_project = 'pybind11'
-breathe_domain_by_extension = {'h': 'cpp'}
+breathe_projects = {"pybind11": ".build/doxygenxml/"}
+breathe_default_project = "pybind11"
+breathe_domain_by_extension = {"h": "cpp"}
 
 # Add any paths that contain templates here, relative to this directory.
-templates_path = ['.templates']
+templates_path = [".templates"]
 
 # The suffix(es) of source filenames.
 # You can specify multiple suffix as a list of string:
 # source_suffix = ['.rst', '.md']
-source_suffix = '.rst'
+source_suffix = ".rst"
 
 # The encoding of source files.
-#source_encoding = 'utf-8-sig'
+# source_encoding = 'utf-8-sig'
 
 # The master toctree document.
-master_doc = 'index'
+master_doc = "index"
 
 # General information about the project.
-project = 'pybind11'
-copyright = '2017, Wenzel Jakob'
-author = 'Wenzel Jakob'
+project = "pybind11"
+copyright = "2017, Wenzel Jakob"
+author = "Wenzel Jakob"
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
@@ -78,37 +82,37 @@ language = None
 
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used:
-#today = ''
+# today = ''
 # Else, today_fmt is used as the format for a strftime call.
-#today_fmt = '%B %d, %Y'
+# today_fmt = '%B %d, %Y'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
-exclude_patterns = ['.build', 'release.rst']
+exclude_patterns = [".build", "release.rst"]
 
 # The reST default role (used for this markup: `text`) to use for all
 # documents.
-default_role = 'any'
+default_role = "any"
 
 # If true, '()' will be appended to :func: etc. cross-reference text.
-#add_function_parentheses = True
+# add_function_parentheses = True
 
 # If true, the current module name will be prepended to all description
 # unit titles (such as .. function::).
-#add_module_names = True
+# add_module_names = True
 
 # If true, sectionauthor and moduleauthor directives will be shown in the
 # output. They are ignored by default.
-#show_authors = False
+# show_authors = False
 
 # The name of the Pygments (syntax highlighting) style to use.
-#pygments_style = 'monokai'
+# pygments_style = 'monokai'
 
 # A list of ignored prefixes for module index sorting.
-#modindex_common_prefix = []
+# modindex_common_prefix = []
 
 # If true, keep warnings as "system message" paragraphs in the built documents.
-#keep_warnings = False
+# keep_warnings = False
 
 # If true, `todo` and `todoList` produce output, else they produce nothing.
 todo_include_todos = False
@@ -119,144 +123,137 @@ todo_include_todos = False
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 
-on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
+on_rtd = os.environ.get("READTHEDOCS", None) == "True"
 
 if not on_rtd:  # only import and set the theme if we're building docs locally
     import sphinx_rtd_theme
-    html_theme = 'sphinx_rtd_theme'
+
+    html_theme = "sphinx_rtd_theme"
     html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
-    html_context = {
-        'css_files': [
-            '_static/theme_overrides.css'
-        ]
-    }
+    html_context = {"css_files": ["_static/theme_overrides.css"]}
 else:
     html_context = {
-        'css_files': [
-            '//media.readthedocs.org/css/sphinx_rtd_theme.css',
-            '//media.readthedocs.org/css/readthedocs-doc-embed.css',
-            '_static/theme_overrides.css'
+        "css_files": [
+            "//media.readthedocs.org/css/sphinx_rtd_theme.css",
+            "//media.readthedocs.org/css/readthedocs-doc-embed.css",
+            "_static/theme_overrides.css",
         ]
     }
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
-#html_theme_options = {}
+# html_theme_options = {}
 
 # Add any paths that contain custom themes here, relative to this directory.
-#html_theme_path = []
+# html_theme_path = []
 
 # The name for this set of Sphinx documents.  If None, it defaults to
 # "<project> v<version> documentation".
-#html_title = None
+# html_title = None
 
 # A shorter title for the navigation bar.  Default is the same as html_title.
-#html_short_title = None
+# html_short_title = None
 
 # The name of an image file (relative to this directory) to place at the top
 # of the sidebar.
-#html_logo = None
+# html_logo = None
 
 # The name of an image file (within the static path) to use as favicon of the
 # docs.  This file should be a Windows icon file (.ico) being 16x16 or 32x32
 # pixels large.
-#html_favicon = None
+# html_favicon = None
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = ["_static"]
 
 # Add any extra paths that contain custom files (such as robots.txt or
 # .htaccess) here, relative to this directory. These files are copied
 # directly to the root of the documentation.
-#html_extra_path = []
+# html_extra_path = []
 
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
-#html_last_updated_fmt = '%b %d, %Y'
+# html_last_updated_fmt = '%b %d, %Y'
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.
-#html_use_smartypants = True
+# html_use_smartypants = True
 
 # Custom sidebar templates, maps document names to template names.
-#html_sidebars = {}
+# html_sidebars = {}
 
 # Additional templates that should be rendered to pages, maps page names to
 # template names.
-#html_additional_pages = {}
+# html_additional_pages = {}
 
 # If false, no module index is generated.
-#html_domain_indices = True
+# html_domain_indices = True
 
 # If false, no index is generated.
-#html_use_index = True
+# html_use_index = True
 
 # If true, the index is split into individual pages for each letter.
-#html_split_index = False
+# html_split_index = False
 
 # If true, links to the reST sources are added to the pages.
-#html_show_sourcelink = True
+# html_show_sourcelink = True
 
 # If true, "Created using Sphinx" is shown in the HTML footer. Default is True.
-#html_show_sphinx = True
+# html_show_sphinx = True
 
 # If true, "(C) Copyright ..." is shown in the HTML footer. Default is True.
-#html_show_copyright = True
+# html_show_copyright = True
 
 # If true, an OpenSearch description file will be output, and all pages will
 # contain a <link> tag referring to it.  The value of this option must be the
 # base URL from which the finished HTML is served.
-#html_use_opensearch = ''
+# html_use_opensearch = ''
 
 # This is the file name suffix for HTML files (e.g. ".xhtml").
-#html_file_suffix = None
+# html_file_suffix = None
 
 # Language to be used for generating the HTML full-text search index.
 # Sphinx supports the following languages:
 #   'da', 'de', 'en', 'es', 'fi', 'fr', 'h', 'it', 'ja'
 #   'nl', 'no', 'pt', 'ro', 'r', 'sv', 'tr'
-#html_search_language = 'en'
+# html_search_language = 'en'
 
 # A dictionary with options for the search language support, empty by default.
 # Now only 'ja' uses this config value
-#html_search_options = {'type': 'default'}
+# html_search_options = {'type': 'default'}
 
 # The name of a javascript file (relative to the configuration directory) that
 # implements a search results scorer. If empty, the default will be used.
-#html_search_scorer = 'scorer.js'
+# html_search_scorer = 'scorer.js'
 
 # Output file base name for HTML help builder.
-htmlhelp_basename = 'pybind11doc'
+htmlhelp_basename = "pybind11doc"
 
 # -- Options for LaTeX output ---------------------------------------------
 
 latex_elements = {
-# The paper size ('letterpaper' or 'a4paper').
-#'papersize': 'letterpaper',
-
-# The font size ('10pt', '11pt' or '12pt').
-#'pointsize': '10pt',
-
-# Additional stuff for the LaTeX preamble.
-'preamble': r'''
+    # The paper size ('letterpaper' or 'a4paper').
+    # 'papersize': 'letterpaper',
+    # The font size ('10pt', '11pt' or '12pt').
+    # 'pointsize': '10pt',
+    # Additional stuff for the LaTeX preamble.
+    "preamble": r"""
 \DeclareUnicodeCharacter{00A0}{}
 \DeclareUnicodeCharacter{2194}{<->}
-''',
-
-# Latex figure (float) alignment
-#'figure_align': 'htbp',
+""",
+    # Latex figure (float) alignment
+    # 'figure_align': 'htbp',
 }
 
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title,
 #  author, documentclass [howto, manual, or own class]).
 latex_documents = [
-  (master_doc, 'pybind11.tex', 'pybind11 Documentation',
-   'Wenzel Jakob', 'manual'),
+    (master_doc, "pybind11.tex", "pybind11 Documentation", "Wenzel Jakob", "manual"),
 ]
 
 # The name of an image file (relative to this directory) to place at the top of
@@ -265,32 +262,29 @@ latex_documents = [
 
 # For "manual" documents, if this is true, then toplevel headings are parts,
 # not chapters.
-#latex_use_parts = False
+# latex_use_parts = False
 
 # If true, show page references after internal links.
-#latex_show_pagerefs = False
+# latex_show_pagerefs = False
 
 # If true, show URL addresses after external links.
-#latex_show_urls = False
+# latex_show_urls = False
 
 # Documents to append as an appendix to all manuals.
-#latex_appendices = []
+# latex_appendices = []
 
 # If false, no module index is generated.
-#latex_domain_indices = True
+# latex_domain_indices = True
 
 
 # -- Options for manual page output ---------------------------------------
 
 # One entry per manual page. List of tuples
 # (source start file, name, description, authors, manual section).
-man_pages = [
-    (master_doc, 'pybind11', 'pybind11 Documentation',
-     [author], 1)
-]
+man_pages = [(master_doc, "pybind11", "pybind11 Documentation", [author], 1)]
 
 # If true, show URL addresses after external links.
-#man_show_urls = False
+# man_show_urls = False
 
 
 # -- Options for Texinfo output -------------------------------------------
@@ -299,35 +293,41 @@ man_pages = [
 # (source start file, target name, title, author,
 #  dir menu entry, description, category)
 texinfo_documents = [
-  (master_doc, 'pybind11', 'pybind11 Documentation',
-   author, 'pybind11', 'One line description of project.',
-   'Miscellaneous'),
+    (
+        master_doc,
+        "pybind11",
+        "pybind11 Documentation",
+        author,
+        "pybind11",
+        "One line description of project.",
+        "Miscellaneous",
+    ),
 ]
 
 # Documents to append as an appendix to all manuals.
-#texinfo_appendices = []
+# texinfo_appendices = []
 
 # If false, no module index is generated.
-#texinfo_domain_indices = True
+# texinfo_domain_indices = True
 
 # How to display URL addresses: 'footnote', 'no', or 'inline'.
-#texinfo_show_urls = 'footnote'
+# texinfo_show_urls = 'footnote'
 
 # If true, do not generate a @detailmenu in the "Top" node's menu.
-#texinfo_no_detailmenu = False
+# texinfo_no_detailmenu = False
 
-primary_domain = 'cpp'
-highlight_language = 'cpp'
+primary_domain = "cpp"
+highlight_language = "cpp"
 
 
 def generate_doxygen_xml(app):
-    build_dir = os.path.join(app.confdir, '.build')
+    build_dir = os.path.join(app.confdir, ".build")
     if not os.path.exists(build_dir):
         os.mkdir(build_dir)
 
     try:
-        subprocess.call(['doxygen', '--version'])
-        retcode = subprocess.call(['doxygen'], cwd=app.confdir)
+        subprocess.call(["doxygen", "--version"])
+        retcode = subprocess.call(["doxygen"], cwd=app.confdir)
         if retcode < 0:
             sys.stderr.write("doxygen error code: {}\n".format(-retcode))
     except OSError as e:

tests/conftest.py

@@ -18,9 +18,9 @@ import env
 # Early diagnostic for failed imports
 import pybind11_tests  # noqa: F401
 
-_unicode_marker = re.compile(r'u(\'[^\']*\')')
-_long_marker = re.compile(r'([0-9])L')
-_hexadecimal = re.compile(r'0x[0-9a-fA-F]+')
+_unicode_marker = re.compile(r"u(\'[^\']*\')")
+_long_marker = re.compile(r"([0-9])L")
+_hexadecimal = re.compile(r"0x[0-9a-fA-F]+")
 
 # Avoid collecting Python3 only files
 collect_ignore = []
@@ -30,7 +30,7 @@ if env.PY2:
 
 def _strip_and_dedent(s):
     """For triple-quote strings"""
-    return textwrap.dedent(s.lstrip('\n').rstrip())
+    return textwrap.dedent(s.lstrip("\n").rstrip())
 
 
 def _split_and_sort(s):
@@ -40,11 +40,14 @@ def _split_and_sort(s):
 
 def _make_explanation(a, b):
     """Explanation for a failed assert -- the a and b arguments are List[str]"""
-    return ["--- actual / +++ expected"] + [line.strip('\n') for line in difflib.ndiff(a, b)]
+    return ["--- actual / +++ expected"] + [
+        line.strip("\n") for line in difflib.ndiff(a, b)
+    ]
 
 
 class Output(object):
     """Basic output post-processing and comparison"""
+
     def __init__(self, string):
         self.string = string
         self.explanation = []
@@ -54,7 +57,11 @@ class Output(object):
 
     def __eq__(self, other):
         # Ignore constructor/destructor output which is prefixed with "###"
-        a = [line for line in self.string.strip().splitlines() if not line.startswith("###")]
+        a = [
+            line
+            for line in self.string.strip().splitlines()
+            if not line.startswith("###")
+        ]
         b = _strip_and_dedent(other).splitlines()
         if a == b:
             return True
@@ -65,6 +72,7 @@ class Output(object):
 
 class Unordered(Output):
     """Custom comparison for output without strict line ordering"""
+
     def __eq__(self, other):
         a = _split_and_sort(self.string)
         b = _split_and_sort(other)
@@ -175,7 +183,7 @@ def msg():
 # noinspection PyUnusedLocal
 def pytest_assertrepr_compare(op, left, right):
     """Hook to insert custom failure explanation"""
-    if hasattr(left, 'explanation'):
+    if hasattr(left, "explanation"):
         return left.explanation
 
 
@@ -189,8 +197,8 @@ def suppress(exception):
 
 
 def gc_collect():
-    ''' Run the garbage collector twice (needed when running
-    reference counting tests with PyPy) '''
+    """Run the garbage collector twice (needed when running
+    reference counting tests with PyPy)"""
     gc.collect()
     gc.collect()
 

tests/test_buffers.py

@@ -46,8 +46,8 @@ def test_to_python():
     mat[3, 2] = 7.0
     assert mat[2, 3] == 4
     assert mat[3, 2] == 7
-    assert struct.unpack_from('f', mat, (3 * 4 + 2) * 4) == (7, )
-    assert struct.unpack_from('f', mat, (2 * 4 + 3) * 4) == (4, )
+    assert struct.unpack_from("f", mat, (3 * 4 + 2) * 4) == (7,)
+    assert struct.unpack_from("f", mat, (2 * 4 + 3) * 4) == (4,)
 
     mat2 = np.array(mat, copy=False)
     assert mat2.shape == (5, 4)
@@ -83,31 +83,31 @@ def test_pointer_to_member_fn():
     for cls in [m.Buffer, m.ConstBuffer, m.DerivedBuffer]:
         buf = cls()
         buf.value = 0x12345678
-        value = struct.unpack('i', bytearray(buf))[0]
+        value = struct.unpack("i", bytearray(buf))[0]
         assert value == 0x12345678
 
 
 def test_readonly_buffer():
     buf = m.BufferReadOnly(0x64)
     view = memoryview(buf)
-    assert view[0] == b'd' if env.PY2 else 0x64
+    assert view[0] == b"d" if env.PY2 else 0x64
     assert view.readonly
 
 
 def test_selective_readonly_buffer():
     buf = m.BufferReadOnlySelect()
 
-    memoryview(buf)[0] = b'd' if env.PY2 else 0x64
+    memoryview(buf)[0] = b"d" if env.PY2 else 0x64
     assert buf.value == 0x64
 
-    io.BytesIO(b'A').readinto(buf)
-    assert buf.value == ord(b'A')
+    io.BytesIO(b"A").readinto(buf)
+    assert buf.value == ord(b"A")
 
     buf.readonly = True
     with pytest.raises(TypeError):
-        memoryview(buf)[0] = b'\0' if env.PY2 else 0
+        memoryview(buf)[0] = b"\0" if env.PY2 else 0
     with pytest.raises(TypeError):
-        io.BytesIO(b'1').readinto(buf)
+        io.BytesIO(b"1").readinto(buf)
 
 
 def test_ctypes_array_1d():

tests/test_builtin_casters.py

@@ -37,79 +37,85 @@ def test_unicode_conversion():
         with pytest.raises(UnicodeDecodeError):
             m.bad_utf8_u8string()
 
-    assert m.u8_Z() == 'Z'
-    assert m.u8_eacute() == u'é'
-    assert m.u16_ibang() == u'‽'
-    assert m.u32_mathbfA() == u'𝐀'
-    assert m.wchar_heart() == u'♥'
+    assert m.u8_Z() == "Z"
+    assert m.u8_eacute() == u"é"
+    assert m.u16_ibang() == u"‽"
+    assert m.u32_mathbfA() == u"𝐀"
+    assert m.wchar_heart() == u"♥"
     if hasattr(m, "has_u8string"):
-        assert m.u8_char8_Z() == 'Z'
+        assert m.u8_char8_Z() == "Z"
 
 
 def test_single_char_arguments():
     """Tests failures for passing invalid inputs to char-accepting functions"""
+
     def toobig_message(r):
         return "Character code point not in range({0:#x})".format(r)
+
     toolong_message = "Expected a character, but multi-character string found"
 
-    assert m.ord_char(u'a') == 0x61  # simple ASCII
-    assert m.ord_char_lv(u'b') == 0x62
-    assert m.ord_char(u'é') == 0xE9  # requires 2 bytes in utf-8, but can be stuffed in a char
+    assert m.ord_char(u"a") == 0x61  # simple ASCII
+    assert m.ord_char_lv(u"b") == 0x62
+    assert (
+        m.ord_char(u"é") == 0xE9
+    )  # requires 2 bytes in utf-8, but can be stuffed in a char
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char(u'Ā') == 0x100  # requires 2 bytes, doesn't fit in a char
+        assert m.ord_char(u"Ā") == 0x100  # requires 2 bytes, doesn't fit in a char
     assert str(excinfo.value) == toobig_message(0x100)
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char(u'ab')
+        assert m.ord_char(u"ab")
     assert str(excinfo.value) == toolong_message
 
-    assert m.ord_char16(u'a') == 0x61
-    assert m.ord_char16(u'é') == 0xE9
-    assert m.ord_char16_lv(u'ê') == 0xEA
-    assert m.ord_char16(u'Ā') == 0x100
-    assert m.ord_char16(u'‽') == 0x203d
-    assert m.ord_char16(u'♥') == 0x2665
-    assert m.ord_char16_lv(u'♡') == 0x2661
+    assert m.ord_char16(u"a") == 0x61
+    assert m.ord_char16(u"é") == 0xE9
+    assert m.ord_char16_lv(u"ê") == 0xEA
+    assert m.ord_char16(u"Ā") == 0x100
+    assert m.ord_char16(u"‽") == 0x203D
+    assert m.ord_char16(u"♥") == 0x2665
+    assert m.ord_char16_lv(u"♡") == 0x2661
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char16(u'🎂') == 0x1F382  # requires surrogate pair
+        assert m.ord_char16(u"🎂") == 0x1F382  # requires surrogate pair
     assert str(excinfo.value) == toobig_message(0x10000)
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char16(u'aa')
+        assert m.ord_char16(u"aa")
     assert str(excinfo.value) == toolong_message
 
-    assert m.ord_char32(u'a') == 0x61
-    assert m.ord_char32(u'é') == 0xE9
-    assert m.ord_char32(u'Ā') == 0x100
-    assert m.ord_char32(u'‽') == 0x203d
-    assert m.ord_char32(u'♥') == 0x2665
-    assert m.ord_char32(u'🎂') == 0x1F382
+    assert m.ord_char32(u"a") == 0x61
+    assert m.ord_char32(u"é") == 0xE9
+    assert m.ord_char32(u"Ā") == 0x100
+    assert m.ord_char32(u"‽") == 0x203D
+    assert m.ord_char32(u"♥") == 0x2665
+    assert m.ord_char32(u"🎂") == 0x1F382
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char32(u'aa')
+        assert m.ord_char32(u"aa")
     assert str(excinfo.value) == toolong_message
 
-    assert m.ord_wchar(u'a') == 0x61
-    assert m.ord_wchar(u'é') == 0xE9
-    assert m.ord_wchar(u'Ā') == 0x100
-    assert m.ord_wchar(u'‽') == 0x203d
-    assert m.ord_wchar(u'♥') == 0x2665
+    assert m.ord_wchar(u"a") == 0x61
+    assert m.ord_wchar(u"é") == 0xE9
+    assert m.ord_wchar(u"Ā") == 0x100
+    assert m.ord_wchar(u"‽") == 0x203D
+    assert m.ord_wchar(u"♥") == 0x2665
     if m.wchar_size == 2:
         with pytest.raises(ValueError) as excinfo:
-            assert m.ord_wchar(u'🎂') == 0x1F382  # requires surrogate pair
+            assert m.ord_wchar(u"🎂") == 0x1F382  # requires surrogate pair
         assert str(excinfo.value) == toobig_message(0x10000)
     else:
-        assert m.ord_wchar(u'🎂') == 0x1F382
+        assert m.ord_wchar(u"🎂") == 0x1F382
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_wchar(u'aa')
+        assert m.ord_wchar(u"aa")
     assert str(excinfo.value) == toolong_message
 
     if hasattr(m, "has_u8string"):
-        assert m.ord_char8(u'a') == 0x61  # simple ASCII
-        assert m.ord_char8_lv(u'b') == 0x62
-        assert m.ord_char8(u'é') == 0xE9  # requires 2 bytes in utf-8, but can be stuffed in a char
+        assert m.ord_char8(u"a") == 0x61  # simple ASCII
+        assert m.ord_char8_lv(u"b") == 0x62
+        assert (
+            m.ord_char8(u"é") == 0xE9
+        )  # requires 2 bytes in utf-8, but can be stuffed in a char
         with pytest.raises(ValueError) as excinfo:
-            assert m.ord_char8(u'Ā') == 0x100  # requires 2 bytes, doesn't fit in a char
+            assert m.ord_char8(u"Ā") == 0x100  # requires 2 bytes, doesn't fit in a char
         assert str(excinfo.value) == toobig_message(0x100)
         with pytest.raises(ValueError) as excinfo:
-            assert m.ord_char8(u'ab')
+            assert m.ord_char8(u"ab")
         assert str(excinfo.value) == toolong_message
 
 
@@ -129,19 +135,19 @@ def test_bytes_to_string():
     assert m.strlen(to_bytes("a\x00b")) == 1  # C-string limitation
 
     # passing in a utf8 encoded string should work
-    assert m.string_length(u'💩'.encode("utf8")) == 4
+    assert m.string_length(u"💩".encode("utf8")) == 4
 
 
 @pytest.mark.skipif(not hasattr(m, "has_string_view"), reason="no <string_view>")
 def test_string_view(capture):
     """Tests support for C++17 string_view arguments and return values"""
     assert m.string_view_chars("Hi") == [72, 105]
-    assert m.string_view_chars("Hi 🎂") == [72, 105, 32, 0xf0, 0x9f, 0x8e, 0x82]
-    assert m.string_view16_chars(u"Hi 🎂") == [72, 105, 32, 0xd83c, 0xdf82]
+    assert m.string_view_chars("Hi 🎂") == [72, 105, 32, 0xF0, 0x9F, 0x8E, 0x82]
+    assert m.string_view16_chars(u"Hi 🎂") == [72, 105, 32, 0xD83C, 0xDF82]
     assert m.string_view32_chars(u"Hi 🎂") == [72, 105, 32, 127874]
     if hasattr(m, "has_u8string"):
         assert m.string_view8_chars("Hi") == [72, 105]
-        assert m.string_view8_chars(u"Hi 🎂") == [72, 105, 32, 0xf0, 0x9f, 0x8e, 0x82]
+        assert m.string_view8_chars(u"Hi 🎂") == [72, 105, 32, 0xF0, 0x9F, 0x8E, 0x82]
 
     assert m.string_view_return() == u"utf8 secret 🎂"
     assert m.string_view16_return() == u"utf16 secret 🎂"
@@ -154,40 +160,52 @@ def test_string_view(capture):
         m.string_view_print("utf8 🎂")
         m.string_view16_print(u"utf16 🎂")
         m.string_view32_print(u"utf32 🎂")
-    assert capture == u"""
+    assert (
+        capture
+        == u"""
         Hi 2
         utf8 🎂 9
         utf16 🎂 8
         utf32 🎂 7
     """
+    )
     if hasattr(m, "has_u8string"):
         with capture:
             m.string_view8_print("Hi")
             m.string_view8_print(u"utf8 🎂")
-        assert capture == u"""
+        assert (
+            capture
+            == u"""
             Hi 2
             utf8 🎂 9
         """
+        )
 
     with capture:
         m.string_view_print("Hi, ascii")
         m.string_view_print("Hi, utf8 🎂")
         m.string_view16_print(u"Hi, utf16 🎂")
         m.string_view32_print(u"Hi, utf32 🎂")
-    assert capture == u"""
+    assert (
+        capture
+        == u"""
         Hi, ascii 9
         Hi, utf8 🎂 13
         Hi, utf16 🎂 12
         Hi, utf32 🎂 11
     """
+    )
     if hasattr(m, "has_u8string"):
         with capture:
             m.string_view8_print("Hi, ascii")
             m.string_view8_print(u"Hi, utf8 🎂")
-        assert capture == u"""
+        assert (
+            capture
+            == u"""
             Hi, ascii 9
             Hi, utf8 🎂 13
         """
+        )
 
 
 def test_integer_casting():
@@ -199,8 +217,14 @@ def test_integer_casting():
     if env.PY2:
         assert m.i32_str(long(-1)) == "-1"  # noqa: F821 undefined name 'long'
         assert m.i64_str(long(-1)) == "-1"  # noqa: F821 undefined name 'long'
-        assert m.i64_str(long(-999999999999)) == "-999999999999"  # noqa: F821 undefined name
-        assert m.u64_str(long(999999999999)) == "999999999999"  # noqa: F821 undefined name 'long'
+        assert (
+            m.i64_str(long(-999999999999))  # noqa: F821 undefined name 'long'
+            == "-999999999999"
+        )
+        assert (
+            m.u64_str(long(999999999999))  # noqa: F821 undefined name 'long'
+            == "999999999999"
+        )
     else:
         assert m.i64_str(-999999999999) == "-999999999999"
         assert m.u64_str(999999999999) == "999999999999"
@@ -236,16 +260,22 @@ def test_tuple(doc):
     assert m.tuple_passthrough([True, "test", 5]) == (5, "test", True)
     assert m.empty_tuple() == ()
 
-    assert doc(m.pair_passthrough) == """
+    assert (
+        doc(m.pair_passthrough)
+        == """
         pair_passthrough(arg0: Tuple[bool, str]) -> Tuple[str, bool]
 
         Return a pair in reversed order
     """
-    assert doc(m.tuple_passthrough) == """
+    )
+    assert (
+        doc(m.tuple_passthrough)
+        == """
         tuple_passthrough(arg0: Tuple[bool, str, int]) -> Tuple[int, str, bool]
 
         Return a triple in reversed order
     """
+    )
 
     assert m.rvalue_pair() == ("rvalue", "rvalue")
     assert m.lvalue_pair() == ("lvalue", "lvalue")
@@ -372,7 +402,7 @@ def test_numpy_bool():
     assert convert(np.bool_(False)) is False
     assert noconvert(np.bool_(True)) is True
     assert noconvert(np.bool_(False)) is False
-    cant_convert(np.zeros(2, dtype='int'))
+    cant_convert(np.zeros(2, dtype="int"))
 
 
 def test_int_long():
@@ -382,7 +412,8 @@ def test_int_long():
     long."""
 
     import sys
-    must_be_long = type(getattr(sys, 'maxint', 1) + 1)
+
+    must_be_long = type(getattr(sys, "maxint", 1) + 1)
     assert isinstance(m.int_cast(), int)
     assert isinstance(m.long_cast(), int)
     assert isinstance(m.longlong_cast(), must_be_long)

tests/test_call_policies.py

@@ -16,10 +16,13 @@ def test_keep_alive_argument(capture):
     with capture:
         p.addChild(m.Child())
         assert ConstructorStats.detail_reg_inst() == n_inst + 1
-    assert capture == """
+    assert (
+        capture
+        == """
         Allocating child.
         Releasing child.
     """
+    )
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
@@ -35,10 +38,13 @@ def test_keep_alive_argument(capture):
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 def test_keep_alive_return_value(capture):
@@ -49,10 +55,13 @@ def test_keep_alive_return_value(capture):
     with capture:
         p.returnChild()
         assert ConstructorStats.detail_reg_inst() == n_inst + 1
-    assert capture == """
+    assert (
+        capture
+        == """
         Allocating child.
         Releasing child.
     """
+    )
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
@@ -68,10 +77,13 @@ def test_keep_alive_return_value(capture):
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 # https://foss.heptapod.net/pypy/pypy/-/issues/2447
@@ -82,14 +94,17 @@ def test_alive_gc(capture):
     p.addChildKeepAlive(m.Child())
     assert ConstructorStats.detail_reg_inst() == n_inst + 2
     lst = [p]
-    lst.append(lst)   # creates a circular reference
+    lst.append(lst)  # creates a circular reference
     with capture:
         del p, lst
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 def test_alive_gc_derived(capture):
@@ -101,14 +116,17 @@ def test_alive_gc_derived(capture):
     p.addChildKeepAlive(m.Child())
     assert ConstructorStats.detail_reg_inst() == n_inst + 2
     lst = [p]
-    lst.append(lst)   # creates a circular reference
+    lst.append(lst)  # creates a circular reference
     with capture:
         del p, lst
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 def test_alive_gc_multi_derived(capture):
@@ -123,15 +141,18 @@ def test_alive_gc_multi_derived(capture):
     # +3 rather than +2 because Derived corresponds to two registered instances
     assert ConstructorStats.detail_reg_inst() == n_inst + 3
     lst = [p]
-    lst.append(lst)   # creates a circular reference
+    lst.append(lst)  # creates a circular reference
     with capture:
         del p, lst
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
         Releasing child.
     """
+    )
 
 
 def test_return_none(capture):
@@ -167,17 +188,23 @@ def test_keep_alive_constructor(capture):
     with capture:
         p = m.Parent(m.Child())
         assert ConstructorStats.detail_reg_inst() == n_inst + 2
-    assert capture == """
+    assert (
+        capture
+        == """
         Allocating child.
         Allocating parent.
     """
+    )
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 def test_call_guard():

tests/test_callbacks.py

@@ -42,17 +42,19 @@ def test_bound_method_callback():
 
 
 def test_keyword_args_and_generalized_unpacking():
-
     def f(*args, **kwargs):
         return args, kwargs
 
     assert m.test_tuple_unpacking(f) == (("positional", 1, 2, 3, 4, 5, 6), {})
-    assert m.test_dict_unpacking(f) == (("positional", 1), {"key": "value", "a": 1, "b": 2})
+    assert m.test_dict_unpacking(f) == (
+        ("positional", 1),
+        {"key": "value", "a": 1, "b": 2},
+    )
     assert m.test_keyword_args(f) == ((), {"x": 10, "y": 20})
     assert m.test_unpacking_and_keywords1(f) == ((1, 2), {"c": 3, "d": 4})
     assert m.test_unpacking_and_keywords2(f) == (
         ("positional", 1, 2, 3, 4, 5),
-        {"key": "value", "a": 1, "b": 2, "c": 3, "d": 4, "e": 5}
+        {"key": "value", "a": 1, "b": 2, "c": 3, "d": 4, "e": 5},
     )
 
     with pytest.raises(TypeError) as excinfo:
@@ -83,12 +85,18 @@ def test_lambda_closure_cleanup():
 def test_cpp_function_roundtrip():
     """Test if passing a function pointer from C++ -> Python -> C++ yields the original pointer"""
 
-    assert m.test_dummy_function(m.dummy_function) == "matches dummy_function: eval(1) = 2"
-    assert (m.test_dummy_function(m.roundtrip(m.dummy_function)) ==
-            "matches dummy_function: eval(1) = 2")
+    assert (
+        m.test_dummy_function(m.dummy_function) == "matches dummy_function: eval(1) = 2"
+    )
+    assert (
+        m.test_dummy_function(m.roundtrip(m.dummy_function))
+        == "matches dummy_function: eval(1) = 2"
+    )
     assert m.roundtrip(None, expect_none=True) is None
-    assert (m.test_dummy_function(lambda x: x + 2) ==
-            "can't convert to function pointer: eval(1) = 3")
+    assert (
+        m.test_dummy_function(lambda x: x + 2)
+        == "can't convert to function pointer: eval(1) = 3"
+    )
 
     with pytest.raises(TypeError) as excinfo:
         m.test_dummy_function(m.dummy_function2)
@@ -96,8 +104,10 @@ def test_cpp_function_roundtrip():
 
     with pytest.raises(TypeError) as excinfo:
         m.test_dummy_function(lambda x, y: x + y)
-    assert any(s in str(excinfo.value) for s in ("missing 1 required positional argument",
-                                                 "takes exactly 2 arguments"))
+    assert any(
+        s in str(excinfo.value)
+        for s in ("missing 1 required positional argument", "takes exactly 2 arguments")
+    )
 
 
 def test_function_signatures(doc):
@@ -127,6 +137,7 @@ def test_async_callbacks():
     m.test_async_callback(gen_f(), work)
     # wait until work is done
     from time import sleep
+
     sleep(0.5)
     assert sum(res) == sum([x + 3 for x in work])
 

tests/test_chrono.py

@@ -80,22 +80,28 @@ SKIP_TZ_ENV_ON_WIN = pytest.mark.skipif(
 )
 
 
-@pytest.mark.parametrize("time1", [
-    datetime.datetime.today().time(),
-    datetime.time(0, 0, 0),
-    datetime.time(0, 0, 0, 1),
-    datetime.time(0, 28, 45, 109827),
-    datetime.time(0, 59, 59, 999999),
-    datetime.time(1, 0, 0),
-    datetime.time(5, 59, 59, 0),
-    datetime.time(5, 59, 59, 1),
-])
-@pytest.mark.parametrize("tz", [
-    None,
-    pytest.param("Europe/Brussels", marks=SKIP_TZ_ENV_ON_WIN),
-    pytest.param("Asia/Pyongyang", marks=SKIP_TZ_ENV_ON_WIN),
-    pytest.param("America/New_York", marks=SKIP_TZ_ENV_ON_WIN),
-])
+@pytest.mark.parametrize(
+    "time1",
+    [
+        datetime.datetime.today().time(),
+        datetime.time(0, 0, 0),
+        datetime.time(0, 0, 0, 1),
+        datetime.time(0, 28, 45, 109827),
+        datetime.time(0, 59, 59, 999999),
+        datetime.time(1, 0, 0),
+        datetime.time(5, 59, 59, 0),
+        datetime.time(5, 59, 59, 1),
+    ],
+)
+@pytest.mark.parametrize(
+    "tz",
+    [
+        None,
+        pytest.param("Europe/Brussels", marks=SKIP_TZ_ENV_ON_WIN),
+        pytest.param("Asia/Pyongyang", marks=SKIP_TZ_ENV_ON_WIN),
+        pytest.param("America/New_York", marks=SKIP_TZ_ENV_ON_WIN),
+    ],
+)
 def test_chrono_system_clock_roundtrip_time(time1, tz, monkeypatch):
     if tz is not None:
         monkeypatch.setenv("TZ", "/usr/share/zoneinfo/{}".format(tz))
@@ -199,7 +205,7 @@ def test_floating_point_duration():
 def test_nano_timepoint():
     time = datetime.datetime.now()
     time1 = m.test_nano_timepoint(time, datetime.timedelta(seconds=60))
-    assert(time1 == time + datetime.timedelta(seconds=60))
+    assert time1 == time + datetime.timedelta(seconds=60)
 
 
 def test_chrono_different_resolutions():

tests/test_class.py

@@ -31,8 +31,10 @@ def test_type():
     with pytest.raises(RuntimeError) as execinfo:
         m.check_type(0)
 
-    assert 'pybind11::detail::get_type_info: unable to find type info' in str(execinfo.value)
-    assert 'Invalid' in str(execinfo.value)
+    assert "pybind11::detail::get_type_info: unable to find type info" in str(
+        execinfo.value
+    )
+    assert "Invalid" in str(execinfo.value)
 
     # Currently not supported
     # See https://github.com/pybind/pybind11/issues/2486
@@ -73,18 +75,24 @@ def test_docstrings(doc):
     assert UserType.get_value.__name__ == "get_value"
     assert UserType.get_value.__module__ == "pybind11_tests"
 
-    assert doc(UserType.get_value) == """
+    assert (
+        doc(UserType.get_value)
+        == """
         get_value(self: m.UserType) -> int
 
         Get value using a method
     """
+    )
     assert doc(UserType.value) == "Get/set value using a property"
 
-    assert doc(m.NoConstructor.new_instance) == """
+    assert (
+        doc(m.NoConstructor.new_instance)
+        == """
         new_instance() -> m.class_.NoConstructor
 
         Return an instance
     """
+    )
 
 
 def test_qualname(doc):
@@ -93,51 +101,69 @@ def test_qualname(doc):
     assert m.NestBase.__qualname__ == "NestBase"
     assert m.NestBase.Nested.__qualname__ == "NestBase.Nested"
 
-    assert doc(m.NestBase.__init__) == """
+    assert (
+        doc(m.NestBase.__init__)
+        == """
         __init__(self: m.class_.NestBase) -> None
     """
-    assert doc(m.NestBase.g) == """
+    )
+    assert (
+        doc(m.NestBase.g)
+        == """
         g(self: m.class_.NestBase, arg0: m.class_.NestBase.Nested) -> None
     """
-    assert doc(m.NestBase.Nested.__init__) == """
+    )
+    assert (
+        doc(m.NestBase.Nested.__init__)
+        == """
         __init__(self: m.class_.NestBase.Nested) -> None
     """
-    assert doc(m.NestBase.Nested.fn) == """
+    )
+    assert (
+        doc(m.NestBase.Nested.fn)
+        == """
         fn(self: m.class_.NestBase.Nested, arg0: int, arg1: m.class_.NestBase, arg2: m.class_.NestBase.Nested) -> None
     """  # noqa: E501 line too long
-    assert doc(m.NestBase.Nested.fa) == """
+    )
+    assert (
+        doc(m.NestBase.Nested.fa)
+        == """
         fa(self: m.class_.NestBase.Nested, a: int, b: m.class_.NestBase, c: m.class_.NestBase.Nested) -> None
     """  # noqa: E501 line too long
+    )
     assert m.NestBase.__module__ == "pybind11_tests.class_"
     assert m.NestBase.Nested.__module__ == "pybind11_tests.class_"
 
 
 def test_inheritance(msg):
-    roger = m.Rabbit('Rabbit')
+    roger = m.Rabbit("Rabbit")
     assert roger.name() + " is a " + roger.species() == "Rabbit is a parrot"
     assert m.pet_name_species(roger) == "Rabbit is a parrot"
 
-    polly = m.Pet('Polly', 'parrot')
+    polly = m.Pet("Polly", "parrot")
     assert polly.name() + " is a " + polly.species() == "Polly is a parrot"
     assert m.pet_name_species(polly) == "Polly is a parrot"
 
-    molly = m.Dog('Molly')
+    molly = m.Dog("Molly")
     assert molly.name() + " is a " + molly.species() == "Molly is a dog"
     assert m.pet_name_species(molly) == "Molly is a dog"
 
-    fred = m.Hamster('Fred')
+    fred = m.Hamster("Fred")
     assert fred.name() + " is a " + fred.species() == "Fred is a rodent"
 
     assert m.dog_bark(molly) == "Woof!"
 
     with pytest.raises(TypeError) as excinfo:
         m.dog_bark(polly)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         dog_bark(): incompatible function arguments. The following argument types are supported:
             1. (arg0: m.class_.Dog) -> str
 
         Invoked with: <m.class_.Pet object at 0>
     """
+    )
 
     with pytest.raises(TypeError) as excinfo:
         m.Chimera("lion", "goat")
@@ -150,6 +176,7 @@ def test_inheritance_init(msg):
     class Python(m.Pet):
         def __init__(self):
             pass
+
     with pytest.raises(TypeError) as exc_info:
         Python()
     expected = "m.class_.Pet.__init__() must be called when overriding __init__"
@@ -191,13 +218,19 @@ def test_mismatched_holder():
 
     with pytest.raises(RuntimeError) as excinfo:
         m.mismatched_holder_1()
-    assert re.match('generic_type: type ".*MismatchDerived1" does not have a non-default '
-                    'holder type while its base ".*MismatchBase1" does', str(excinfo.value))
+    assert re.match(
+        'generic_type: type ".*MismatchDerived1" does not have a non-default '
+        'holder type while its base ".*MismatchBase1" does',
+        str(excinfo.value),
+    )
 
     with pytest.raises(RuntimeError) as excinfo:
         m.mismatched_holder_2()
-    assert re.match('generic_type: type ".*MismatchDerived2" has a non-default holder type '
-                    'while its base ".*MismatchBase2" does not', str(excinfo.value))
+    assert re.match(
+        'generic_type: type ".*MismatchDerived2" has a non-default holder type '
+        'while its base ".*MismatchBase2" does not',
+        str(excinfo.value),
+    )
 
 
 def test_override_static():
@@ -229,20 +262,20 @@ def test_operator_new_delete(capture):
         a = m.HasOpNewDel()
         b = m.HasOpNewDelSize()
         d = m.HasOpNewDelBoth()
-    assert capture == """
+    assert (
+        capture
+        == """
         A new 8
         B new 4
         D new 32
     """
+    )
     sz_alias = str(m.AliasedHasOpNewDelSize.size_alias)
     sz_noalias = str(m.AliasedHasOpNewDelSize.size_noalias)
     with capture:
         c = m.AliasedHasOpNewDelSize()
         c2 = SubAliased()
-    assert capture == (
-        "C new " + sz_noalias + "\n" +
-        "C new " + sz_alias + "\n"
-    )
+    assert capture == ("C new " + sz_noalias + "\n" + "C new " + sz_alias + "\n")
 
     with capture:
         del a
@@ -251,21 +284,21 @@ def test_operator_new_delete(capture):
         pytest.gc_collect()
         del d
         pytest.gc_collect()
-    assert capture == """
+    assert (
+        capture
+        == """
         A delete
         B delete 4
         D delete
     """
+    )
 
     with capture:
         del c
         pytest.gc_collect()
         del c2
         pytest.gc_collect()
-    assert capture == (
-        "C delete " + sz_noalias + "\n" +
-        "C delete " + sz_alias + "\n"
-    )
+    assert capture == ("C delete " + sz_noalias + "\n" + "C delete " + sz_alias + "\n")
 
 
 def test_bind_protected_functions():
@@ -325,19 +358,23 @@ def test_reentrant_implicit_conversion_failure(msg):
     # ensure that there is no runaway reentrant implicit conversion (#1035)
     with pytest.raises(TypeError) as excinfo:
         m.BogusImplicitConversion(0)
-    assert msg(excinfo.value) == '''
+    assert (
+        msg(excinfo.value)
+        == """
         __init__(): incompatible constructor arguments. The following argument types are supported:
             1. m.class_.BogusImplicitConversion(arg0: m.class_.BogusImplicitConversion)
 
         Invoked with: 0
-    '''
+    """
+    )
 
 
 def test_error_after_conversions():
     with pytest.raises(TypeError) as exc_info:
         m.test_error_after_conversions("hello")
     assert str(exc_info.value).startswith(
-        "Unable to convert function return value to a Python type!")
+        "Unable to convert function return value to a Python type!"
+    )
 
 
 def test_aligned():
@@ -350,8 +387,10 @@ def test_aligned():
 @pytest.mark.xfail("env.PYPY")
 def test_final():
     with pytest.raises(TypeError) as exc_info:
+
         class PyFinalChild(m.IsFinal):
             pass
+
     assert str(exc_info.value).endswith("is not an acceptable base type")
 
 
@@ -359,8 +398,10 @@ def test_final():
 @pytest.mark.xfail("env.PYPY")
 def test_non_final_final():
     with pytest.raises(TypeError) as exc_info:
+
         class PyNonFinalFinalChild(m.IsNonFinalFinal):
             pass
+
     assert str(exc_info.value).endswith("is not an acceptable base type")
 
 
@@ -396,11 +437,14 @@ def test_base_and_derived_nested_scope():
 @pytest.mark.skip("See https://github.com/pybind/pybind11/pull/2564")
 def test_register_duplicate_class():
     import types
+
     module_scope = types.ModuleType("module_scope")
     with pytest.raises(RuntimeError) as exc_info:
         m.register_duplicate_class_name(module_scope)
-    expected = ('generic_type: cannot initialize type "Duplicate": '
-                'an object with that name is already defined')
+    expected = (
+        'generic_type: cannot initialize type "Duplicate": '
+        "an object with that name is already defined"
+    )
     assert str(exc_info.value) == expected
     with pytest.raises(RuntimeError) as exc_info:
         m.register_duplicate_class_type(module_scope)
@@ -409,10 +453,13 @@ def test_register_duplicate_class():
 
     class ClassScope:
         pass
+
     with pytest.raises(RuntimeError) as exc_info:
         m.register_duplicate_nested_class_name(ClassScope)
-    expected = ('generic_type: cannot initialize type "DuplicateNested": '
-                'an object with that name is already defined')
+    expected = (
+        'generic_type: cannot initialize type "DuplicateNested": '
+        "an object with that name is already defined"
+    )
     assert str(exc_info.value) == expected
     with pytest.raises(RuntimeError) as exc_info:
         m.register_duplicate_nested_class_type(ClassScope)

tests/test_copy_move.py

@@ -19,7 +19,11 @@ def test_move_and_copy_casts():
     """Cast some values in C++ via custom type casters and count the number of moves/copies."""
 
     cstats = m.move_and_copy_cstats()
-    c_m, c_mc, c_c = cstats["MoveOnlyInt"], cstats["MoveOrCopyInt"], cstats["CopyOnlyInt"]
+    c_m, c_mc, c_c = (
+        cstats["MoveOnlyInt"],
+        cstats["MoveOrCopyInt"],
+        cstats["CopyOnlyInt"],
+    )
 
     # The type move constructions/assignments below each get incremented: the move assignment comes
     # from the type_caster load; the move construction happens when extracting that via a cast or
@@ -43,7 +47,11 @@ def test_move_and_copy_loads():
     moves/copies."""
 
     cstats = m.move_and_copy_cstats()
-    c_m, c_mc, c_c = cstats["MoveOnlyInt"], cstats["MoveOrCopyInt"], cstats["CopyOnlyInt"]
+    c_m, c_mc, c_c = (
+        cstats["MoveOnlyInt"],
+        cstats["MoveOrCopyInt"],
+        cstats["CopyOnlyInt"],
+    )
 
     assert m.move_only(10) == 10  # 1 move, c_m
     assert m.move_or_copy(11) == 11  # 1 move, c_mc
@@ -66,12 +74,16 @@ def test_move_and_copy_loads():
     assert c_m.alive() + c_mc.alive() + c_c.alive() == 0
 
 
-@pytest.mark.skipif(not m.has_optional, reason='no <optional>')
+@pytest.mark.skipif(not m.has_optional, reason="no <optional>")
 def test_move_and_copy_load_optional():
     """Tests move/copy loads of std::optional arguments"""
 
     cstats = m.move_and_copy_cstats()
-    c_m, c_mc, c_c = cstats["MoveOnlyInt"], cstats["MoveOrCopyInt"], cstats["CopyOnlyInt"]
+    c_m, c_mc, c_c = (
+        cstats["MoveOnlyInt"],
+        cstats["MoveOrCopyInt"],
+        cstats["CopyOnlyInt"],
+    )
 
     # The extra move/copy constructions below come from the std::optional move (which has to move
     # its arguments):

tests/test_custom_type_casters.py

@@ -5,65 +5,91 @@ from pybind11_tests import custom_type_casters as m
 
 def test_noconvert_args(msg):
     a = m.ArgInspector()
-    assert msg(a.f("hi")) == """
+    assert (
+        msg(a.f("hi"))
+        == """
         loading ArgInspector1 argument WITH conversion allowed.  Argument value = hi
     """
-    assert msg(a.g("this is a", "this is b")) == """
+    )
+    assert (
+        msg(a.g("this is a", "this is b"))
+        == """
         loading ArgInspector1 argument WITHOUT conversion allowed.  Argument value = this is a
         loading ArgInspector1 argument WITH conversion allowed.  Argument value = this is b
         13
         loading ArgInspector2 argument WITH conversion allowed.  Argument value = (default arg inspector 2)
     """  # noqa: E501 line too long
-    assert msg(a.g("this is a", "this is b", 42)) == """
+    )
+    assert (
+        msg(a.g("this is a", "this is b", 42))
+        == """
         loading ArgInspector1 argument WITHOUT conversion allowed.  Argument value = this is a
         loading ArgInspector1 argument WITH conversion allowed.  Argument value = this is b
         42
         loading ArgInspector2 argument WITH conversion allowed.  Argument value = (default arg inspector 2)
     """  # noqa: E501 line too long
-    assert msg(a.g("this is a", "this is b", 42, "this is d")) == """
+    )
+    assert (
+        msg(a.g("this is a", "this is b", 42, "this is d"))
+        == """
         loading ArgInspector1 argument WITHOUT conversion allowed.  Argument value = this is a
         loading ArgInspector1 argument WITH conversion allowed.  Argument value = this is b
         42
         loading ArgInspector2 argument WITH conversion allowed.  Argument value = this is d
     """
-    assert (a.h("arg 1") ==
-            "loading ArgInspector2 argument WITHOUT conversion allowed.  Argument value = arg 1")
-    assert msg(m.arg_inspect_func("A1", "A2")) == """
+    )
+    assert (
+        a.h("arg 1")
+        == "loading ArgInspector2 argument WITHOUT conversion allowed.  Argument value = arg 1"
+    )
+    assert (
+        msg(m.arg_inspect_func("A1", "A2"))
+        == """
         loading ArgInspector2 argument WITH conversion allowed.  Argument value = A1
         loading ArgInspector1 argument WITHOUT conversion allowed.  Argument value = A2
     """
+    )
 
     assert m.floats_preferred(4) == 2.0
     assert m.floats_only(4.0) == 2.0
     with pytest.raises(TypeError) as excinfo:
         m.floats_only(4)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         floats_only(): incompatible function arguments. The following argument types are supported:
             1. (f: float) -> float
 
         Invoked with: 4
     """
+    )
 
     assert m.ints_preferred(4) == 2
     assert m.ints_preferred(True) == 0
     with pytest.raises(TypeError) as excinfo:
         m.ints_preferred(4.0)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         ints_preferred(): incompatible function arguments. The following argument types are supported:
             1. (i: int) -> int
 
         Invoked with: 4.0
     """  # noqa: E501 line too long
+    )
 
     assert m.ints_only(4) == 2
     with pytest.raises(TypeError) as excinfo:
         m.ints_only(4.0)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         ints_only(): incompatible function arguments. The following argument types are supported:
             1. (i: int) -> int
 
         Invoked with: 4.0
     """
+    )
 
 
 def test_custom_caster_destruction():

tests/test_docstring_options.py

@@ -18,10 +18,10 @@ def test_docstring_options():
     assert m.test_overloaded3.__doc__ == "Overload docstr"
 
     # options.enable_function_signatures()
-    assert m.test_function3.__doc__ .startswith("test_function3(a: int, b: int) -> None")
+    assert m.test_function3.__doc__.startswith("test_function3(a: int, b: int) -> None")
 
-    assert m.test_function4.__doc__ .startswith("test_function4(a: int, b: int) -> None")
-    assert m.test_function4.__doc__ .endswith("A custom docstring\n")
+    assert m.test_function4.__doc__.startswith("test_function4(a: int, b: int) -> None")
+    assert m.test_function4.__doc__.endswith("A custom docstring\n")
 
     # options.disable_function_signatures()
     # options.disable_user_defined_docstrings()
@@ -31,8 +31,8 @@ def test_docstring_options():
     assert m.test_function6.__doc__ == "A custom docstring"
 
     # RAII destructor
-    assert m.test_function7.__doc__ .startswith("test_function7(a: int, b: int) -> None")
-    assert m.test_function7.__doc__ .endswith("A custom docstring\n")
+    assert m.test_function7.__doc__.startswith("test_function7(a: int, b: int) -> None")
+    assert m.test_function7.__doc__.endswith("A custom docstring\n")
 
     # Suppression of user-defined docstrings for non-function objects
     assert not m.DocstringTestFoo.__doc__

tests/test_eigen.py

@@ -6,11 +6,15 @@ np = pytest.importorskip("numpy")
 m = pytest.importorskip("pybind11_tests.eigen")
 
 
-ref = np.array([[ 0.,  3,  0,  0,  0, 11],
-                [22,  0,  0,  0, 17, 11],
-                [ 7,  5,  0,  1,  0, 11],
-                [ 0,  0,  0,  0,  0, 11],
-                [ 0,  0, 14,  0,  8, 11]])
+ref = np.array(
+    [
+        [0.0, 3, 0, 0, 0, 11],
+        [22, 0, 0, 0, 17, 11],
+        [7, 5, 0, 1, 0, 11],
+        [0, 0, 0, 0, 0, 11],
+        [0, 0, 14, 0, 8, 11],
+    ]
+)
 
 
 def assert_equal_ref(mat):
@@ -40,28 +44,37 @@ def test_dense():
 
 
 def test_partially_fixed():
-    ref2 = np.array([[0., 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [12, 13, 14, 15]])
+    ref2 = np.array([[0.0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [12, 13, 14, 15]])
     np.testing.assert_array_equal(m.partial_copy_four_rm_r(ref2), ref2)
     np.testing.assert_array_equal(m.partial_copy_four_rm_c(ref2), ref2)
     np.testing.assert_array_equal(m.partial_copy_four_rm_r(ref2[:, 1]), ref2[:, [1]])
     np.testing.assert_array_equal(m.partial_copy_four_rm_c(ref2[0, :]), ref2[[0], :])
-    np.testing.assert_array_equal(m.partial_copy_four_rm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)])
     np.testing.assert_array_equal(
-        m.partial_copy_four_rm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :])
+        m.partial_copy_four_rm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)]
+    )
+    np.testing.assert_array_equal(
+        m.partial_copy_four_rm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :]
+    )
 
     np.testing.assert_array_equal(m.partial_copy_four_cm_r(ref2), ref2)
     np.testing.assert_array_equal(m.partial_copy_four_cm_c(ref2), ref2)
     np.testing.assert_array_equal(m.partial_copy_four_cm_r(ref2[:, 1]), ref2[:, [1]])
     np.testing.assert_array_equal(m.partial_copy_four_cm_c(ref2[0, :]), ref2[[0], :])
-    np.testing.assert_array_equal(m.partial_copy_four_cm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)])
     np.testing.assert_array_equal(
-        m.partial_copy_four_cm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :])
+        m.partial_copy_four_cm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)]
+    )
+    np.testing.assert_array_equal(
+        m.partial_copy_four_cm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :]
+    )
 
     # TypeError should be raise for a shape mismatch
-    functions = [m.partial_copy_four_rm_r, m.partial_copy_four_rm_c,
-                 m.partial_copy_four_cm_r, m.partial_copy_four_cm_c]
-    matrix_with_wrong_shape = [[1, 2],
-                               [3, 4]]
+    functions = [
+        m.partial_copy_four_rm_r,
+        m.partial_copy_four_rm_c,
+        m.partial_copy_four_cm_r,
+        m.partial_copy_four_cm_c,
+    ]
+    matrix_with_wrong_shape = [[1, 2], [3, 4]]
     for f in functions:
         with pytest.raises(TypeError) as excinfo:
             f(matrix_with_wrong_shape)
@@ -69,7 +82,7 @@ def test_partially_fixed():
 
 
 def test_mutator_descriptors():
-    zr = np.arange(30, dtype='float32').reshape(5, 6)  # row-major
+    zr = np.arange(30, dtype="float32").reshape(5, 6)  # row-major
     zc = zr.reshape(6, 5).transpose()  # column-major
 
     m.fixed_mutator_r(zr)
@@ -78,18 +91,21 @@ def test_mutator_descriptors():
     m.fixed_mutator_a(zc)
     with pytest.raises(TypeError) as excinfo:
         m.fixed_mutator_r(zc)
-    assert ('(arg0: numpy.ndarray[numpy.float32[5, 6],'
-            ' flags.writeable, flags.c_contiguous]) -> None'
-            in str(excinfo.value))
+    assert (
+        "(arg0: numpy.ndarray[numpy.float32[5, 6],"
+        " flags.writeable, flags.c_contiguous]) -> None" in str(excinfo.value)
+    )
     with pytest.raises(TypeError) as excinfo:
         m.fixed_mutator_c(zr)
-    assert ('(arg0: numpy.ndarray[numpy.float32[5, 6],'
-            ' flags.writeable, flags.f_contiguous]) -> None'
-            in str(excinfo.value))
+    assert (
+        "(arg0: numpy.ndarray[numpy.float32[5, 6],"
+        " flags.writeable, flags.f_contiguous]) -> None" in str(excinfo.value)
+    )
     with pytest.raises(TypeError) as excinfo:
-        m.fixed_mutator_a(np.array([[1, 2], [3, 4]], dtype='float32'))
-    assert ('(arg0: numpy.ndarray[numpy.float32[5, 6], flags.writeable]) -> None'
-            in str(excinfo.value))
+        m.fixed_mutator_a(np.array([[1, 2], [3, 4]], dtype="float32"))
+    assert "(arg0: numpy.ndarray[numpy.float32[5, 6], flags.writeable]) -> None" in str(
+        excinfo.value
+    )
     zr.flags.writeable = False
     with pytest.raises(TypeError):
         m.fixed_mutator_r(zr)
@@ -98,26 +114,26 @@ def test_mutator_descriptors():
 
 
 def test_cpp_casting():
-    assert m.cpp_copy(m.fixed_r()) == 22.
-    assert m.cpp_copy(m.fixed_c()) == 22.
-    z = np.array([[5., 6], [7, 8]])
-    assert m.cpp_copy(z) == 7.
-    assert m.cpp_copy(m.get_cm_ref()) == 21.
-    assert m.cpp_copy(m.get_rm_ref()) == 21.
-    assert m.cpp_ref_c(m.get_cm_ref()) == 21.
-    assert m.cpp_ref_r(m.get_rm_ref()) == 21.
+    assert m.cpp_copy(m.fixed_r()) == 22.0
+    assert m.cpp_copy(m.fixed_c()) == 22.0
+    z = np.array([[5.0, 6], [7, 8]])
+    assert m.cpp_copy(z) == 7.0
+    assert m.cpp_copy(m.get_cm_ref()) == 21.0
+    assert m.cpp_copy(m.get_rm_ref()) == 21.0
+    assert m.cpp_ref_c(m.get_cm_ref()) == 21.0
+    assert m.cpp_ref_r(m.get_rm_ref()) == 21.0
     with pytest.raises(RuntimeError) as excinfo:
         # Can't reference m.fixed_c: it contains floats, m.cpp_ref_any wants doubles
         m.cpp_ref_any(m.fixed_c())
-    assert 'Unable to cast Python instance' in str(excinfo.value)
+    assert "Unable to cast Python instance" in str(excinfo.value)
     with pytest.raises(RuntimeError) as excinfo:
         # Can't reference m.fixed_r: it contains floats, m.cpp_ref_any wants doubles
         m.cpp_ref_any(m.fixed_r())
-    assert 'Unable to cast Python instance' in str(excinfo.value)
-    assert m.cpp_ref_any(m.ReturnTester.create()) == 1.
+    assert "Unable to cast Python instance" in str(excinfo.value)
+    assert m.cpp_ref_any(m.ReturnTester.create()) == 1.0
 
-    assert m.cpp_ref_any(m.get_cm_ref()) == 21.
-    assert m.cpp_ref_any(m.get_cm_ref()) == 21.
+    assert m.cpp_ref_any(m.get_cm_ref()) == 21.0
+    assert m.cpp_ref_any(m.get_cm_ref()) == 21.0
 
 
 def test_pass_readonly_array():
@@ -149,7 +165,7 @@ def test_nonunit_stride_from_python():
     # Mutator:
     m.double_threer(second_row)
     m.double_threec(second_col)
-    np.testing.assert_array_equal(counting_mat, [[0., 2, 2], [6, 16, 10], [6, 14, 8]])
+    np.testing.assert_array_equal(counting_mat, [[0.0, 2, 2], [6, 16, 10], [6, 14, 8]])
 
 
 def test_negative_stride_from_python(msg):
@@ -178,26 +194,36 @@ def test_negative_stride_from_python(msg):
     # Mutator:
     with pytest.raises(TypeError) as excinfo:
         m.double_threer(second_row)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         double_threer(): incompatible function arguments. The following argument types are supported:
             1. (arg0: numpy.ndarray[numpy.float32[1, 3], flags.writeable]) -> None
 
-        Invoked with: """ + repr(np.array([ 5.,  4.,  3.], dtype='float32'))  # noqa: E501 line too long
+        Invoked with: """  # noqa: E501 line too long
+        + repr(np.array([5.0, 4.0, 3.0], dtype="float32"))
+    )
 
     with pytest.raises(TypeError) as excinfo:
         m.double_threec(second_col)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         double_threec(): incompatible function arguments. The following argument types are supported:
             1. (arg0: numpy.ndarray[numpy.float32[3, 1], flags.writeable]) -> None
 
-        Invoked with: """ + repr(np.array([ 7.,  4.,  1.], dtype='float32'))  # noqa: E501 line too long
+        Invoked with: """  # noqa: E501 line too long
+        + repr(np.array([7.0, 4.0, 1.0], dtype="float32"))
+    )
 
 
 def test_nonunit_stride_to_python():
     assert np.all(m.diagonal(ref) == ref.diagonal())
     assert np.all(m.diagonal_1(ref) == ref.diagonal(1))
     for i in range(-5, 7):
-        assert np.all(m.diagonal_n(ref, i) == ref.diagonal(i)), "m.diagonal_n({})".format(i)
+        assert np.all(
+            m.diagonal_n(ref, i) == ref.diagonal(i)
+        ), "m.diagonal_n({})".format(i)
 
     assert np.all(m.block(ref, 2, 1, 3, 3) == ref[2:5, 1:4])
     assert np.all(m.block(ref, 1, 4, 4, 2) == ref[1:, 4:])
@@ -207,8 +233,10 @@ def test_nonunit_stride_to_python():
 def test_eigen_ref_to_python():
     chols = [m.cholesky1, m.cholesky2, m.cholesky3, m.cholesky4]
     for i, chol in enumerate(chols, start=1):
-        mymat = chol(np.array([[1., 2, 4], [2, 13, 23], [4, 23, 77]]))
-        assert np.all(mymat == np.array([[1, 0, 0], [2, 3, 0], [4, 5, 6]])), "cholesky{}".format(i)
+        mymat = chol(np.array([[1.0, 2, 4], [2, 13, 23], [4, 23, 77]]))
+        assert np.all(
+            mymat == np.array([[1, 0, 0], [2, 3, 0], [4, 5, 6]])
+        ), "cholesky{}".format(i)
 
 
 def assign_both(a1, a2, r, c, v):
@@ -325,8 +353,12 @@ def test_eigen_return_references():
     np.testing.assert_array_equal(a_block1, master[3:5, 3:5])
     np.testing.assert_array_equal(a_block2, master[2:5, 2:4])
     np.testing.assert_array_equal(a_block3, master[6:10, 7:10])
-    np.testing.assert_array_equal(a_corn1, master[0::master.shape[0] - 1, 0::master.shape[1] - 1])
-    np.testing.assert_array_equal(a_corn2, master[0::master.shape[0] - 1, 0::master.shape[1] - 1])
+    np.testing.assert_array_equal(
+        a_corn1, master[0 :: master.shape[0] - 1, 0 :: master.shape[1] - 1]
+    )
+    np.testing.assert_array_equal(
+        a_corn2, master[0 :: master.shape[0] - 1, 0 :: master.shape[1] - 1]
+    )
 
     np.testing.assert_array_equal(a_copy1, c1want)
     np.testing.assert_array_equal(a_copy2, c2want)
@@ -355,16 +387,28 @@ def test_eigen_keepalive():
     cstats = ConstructorStats.get(m.ReturnTester)
     assert cstats.alive() == 1
     unsafe = [a.ref(), a.ref_const(), a.block(1, 2, 3, 4)]
-    copies = [a.copy_get(), a.copy_view(), a.copy_ref(), a.copy_ref_const(),
-              a.copy_block(4, 3, 2, 1)]
+    copies = [
+        a.copy_get(),
+        a.copy_view(),
+        a.copy_ref(),
+        a.copy_ref_const(),
+        a.copy_block(4, 3, 2, 1),
+    ]
     del a
     assert cstats.alive() == 0
     del unsafe
     del copies
 
-    for meth in [m.ReturnTester.get, m.ReturnTester.get_ptr, m.ReturnTester.view,
-                 m.ReturnTester.view_ptr, m.ReturnTester.ref_safe, m.ReturnTester.ref_const_safe,
-                 m.ReturnTester.corners, m.ReturnTester.corners_const]:
+    for meth in [
+        m.ReturnTester.get,
+        m.ReturnTester.get_ptr,
+        m.ReturnTester.view,
+        m.ReturnTester.view_ptr,
+        m.ReturnTester.ref_safe,
+        m.ReturnTester.ref_const_safe,
+        m.ReturnTester.corners,
+        m.ReturnTester.corners_const,
+    ]:
         assert_keeps_alive(m.ReturnTester, meth)
 
     for meth in [m.ReturnTester.block_safe, m.ReturnTester.block_const]:
@@ -374,18 +418,18 @@ def test_eigen_keepalive():
 def test_eigen_ref_mutators():
     """Tests Eigen's ability to mutate numpy values"""
 
-    orig = np.array([[1., 2, 3], [4, 5, 6], [7, 8, 9]])
+    orig = np.array([[1.0, 2, 3], [4, 5, 6], [7, 8, 9]])
     zr = np.array(orig)
-    zc = np.array(orig, order='F')
+    zc = np.array(orig, order="F")
     m.add_rm(zr, 1, 0, 100)
-    assert np.all(zr == np.array([[1., 2, 3], [104, 5, 6], [7, 8, 9]]))
+    assert np.all(zr == np.array([[1.0, 2, 3], [104, 5, 6], [7, 8, 9]]))
     m.add_cm(zc, 1, 0, 200)
-    assert np.all(zc == np.array([[1., 2, 3], [204, 5, 6], [7, 8, 9]]))
+    assert np.all(zc == np.array([[1.0, 2, 3], [204, 5, 6], [7, 8, 9]]))
 
     m.add_any(zr, 1, 0, 20)
-    assert np.all(zr == np.array([[1., 2, 3], [124, 5, 6], [7, 8, 9]]))
+    assert np.all(zr == np.array([[1.0, 2, 3], [124, 5, 6], [7, 8, 9]]))
     m.add_any(zc, 1, 0, 10)
-    assert np.all(zc == np.array([[1., 2, 3], [214, 5, 6], [7, 8, 9]]))
+    assert np.all(zc == np.array([[1.0, 2, 3], [214, 5, 6], [7, 8, 9]]))
 
     # Can't reference a col-major array with a row-major Ref, and vice versa:
     with pytest.raises(TypeError):
@@ -406,8 +450,8 @@ def test_eigen_ref_mutators():
     cornersr = zr[0::2, 0::2]
     cornersc = zc[0::2, 0::2]
 
-    assert np.all(cornersr == np.array([[1., 3], [7, 9]]))
-    assert np.all(cornersc == np.array([[1., 3], [7, 9]]))
+    assert np.all(cornersr == np.array([[1.0, 3], [7, 9]]))
+    assert np.all(cornersc == np.array([[1.0, 3], [7, 9]]))
 
     with pytest.raises(TypeError):
         m.add_rm(cornersr, 0, 1, 25)
@@ -419,8 +463,8 @@ def test_eigen_ref_mutators():
         m.add_cm(cornersc, 0, 1, 25)
     m.add_any(cornersr, 0, 1, 25)
     m.add_any(cornersc, 0, 1, 44)
-    assert np.all(zr == np.array([[1., 2, 28], [4, 5, 6], [7, 8, 9]]))
-    assert np.all(zc == np.array([[1., 2, 47], [4, 5, 6], [7, 8, 9]]))
+    assert np.all(zr == np.array([[1.0, 2, 28], [4, 5, 6], [7, 8, 9]]))
+    assert np.all(zc == np.array([[1.0, 2, 47], [4, 5, 6], [7, 8, 9]]))
 
     # You shouldn't be allowed to pass a non-writeable array to a mutating Eigen method:
     zro = zr[0:4, 0:4]
@@ -458,7 +502,7 @@ def test_numpy_ref_mutators():
     assert not zrro.flags.owndata and not zrro.flags.writeable
 
     zc[1, 2] = 99
-    expect = np.array([[11., 12, 13], [21, 22, 99], [31, 32, 33]])
+    expect = np.array([[11.0, 12, 13], [21, 22, 99], [31, 32, 33]])
     # We should have just changed zc, of course, but also zcro and the original eigen matrix
     assert np.all(zc == expect)
     assert np.all(zcro == expect)
@@ -506,18 +550,20 @@ def test_both_ref_mutators():
     assert np.all(z == z3)
     assert np.all(z == z4)
     assert np.all(z == z5)
-    expect = np.array([[0., 22, 20], [31, 37, 33], [41, 42, 38]])
+    expect = np.array([[0.0, 22, 20], [31, 37, 33], [41, 42, 38]])
     assert np.all(z == expect)
 
-    y = np.array(range(100), dtype='float64').reshape(10, 10)
+    y = np.array(range(100), dtype="float64").reshape(10, 10)
     y2 = m.incr_matrix_any(y, 10)  # np -> eigen -> np
-    y3 = m.incr_matrix_any(y2[0::2, 0::2], -33)  # np -> eigen -> np slice -> np -> eigen -> np
+    y3 = m.incr_matrix_any(
+        y2[0::2, 0::2], -33
+    )  # np -> eigen -> np slice -> np -> eigen -> np
     y4 = m.even_rows(y3)  # numpy -> eigen slice -> (... y3)
     y5 = m.even_cols(y4)  # numpy -> eigen slice -> (... y4)
     y6 = m.incr_matrix_any(y5, 1000)  # numpy -> eigen -> (... y5)
 
     # Apply same mutations using just numpy:
-    yexpect = np.array(range(100), dtype='float64').reshape(10, 10)
+    yexpect = np.array(range(100), dtype="float64").reshape(10, 10)
     yexpect += 10
     yexpect[0::2, 0::2] -= 33
     yexpect[0::4, 0::4] += 1000
@@ -532,10 +578,14 @@ def test_both_ref_mutators():
 def test_nocopy_wrapper():
     # get_elem requires a column-contiguous matrix reference, but should be
     # callable with other types of matrix (via copying):
-    int_matrix_colmajor = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]], order='F')
-    dbl_matrix_colmajor = np.array(int_matrix_colmajor, dtype='double', order='F', copy=True)
-    int_matrix_rowmajor = np.array(int_matrix_colmajor, order='C', copy=True)
-    dbl_matrix_rowmajor = np.array(int_matrix_rowmajor, dtype='double', order='C', copy=True)
+    int_matrix_colmajor = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]], order="F")
+    dbl_matrix_colmajor = np.array(
+        int_matrix_colmajor, dtype="double", order="F", copy=True
+    )
+    int_matrix_rowmajor = np.array(int_matrix_colmajor, order="C", copy=True)
+    dbl_matrix_rowmajor = np.array(
+        int_matrix_rowmajor, dtype="double", order="C", copy=True
+    )
 
     # All should be callable via get_elem:
     assert m.get_elem(int_matrix_colmajor) == 8
@@ -546,32 +596,38 @@ def test_nocopy_wrapper():
     # All but the second should fail with m.get_elem_nocopy:
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_nocopy(int_matrix_colmajor)
-    assert ('get_elem_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.f_contiguous' in str(excinfo.value))
+    assert "get_elem_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.f_contiguous" in str(excinfo.value)
     assert m.get_elem_nocopy(dbl_matrix_colmajor) == 8
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_nocopy(int_matrix_rowmajor)
-    assert ('get_elem_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.f_contiguous' in str(excinfo.value))
+    assert "get_elem_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.f_contiguous" in str(excinfo.value)
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_nocopy(dbl_matrix_rowmajor)
-    assert ('get_elem_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.f_contiguous' in str(excinfo.value))
+    assert "get_elem_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.f_contiguous" in str(excinfo.value)
 
     # For the row-major test, we take a long matrix in row-major, so only the third is allowed:
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_rm_nocopy(int_matrix_colmajor)
-    assert ('get_elem_rm_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.c_contiguous' in str(excinfo.value))
+    assert "get_elem_rm_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.c_contiguous" in str(excinfo.value)
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_rm_nocopy(dbl_matrix_colmajor)
-    assert ('get_elem_rm_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.c_contiguous' in str(excinfo.value))
+    assert "get_elem_rm_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.c_contiguous" in str(excinfo.value)
     assert m.get_elem_rm_nocopy(int_matrix_rowmajor) == 8
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_rm_nocopy(dbl_matrix_rowmajor)
-    assert ('get_elem_rm_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.c_contiguous' in str(excinfo.value))
+    assert "get_elem_rm_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.c_contiguous" in str(excinfo.value)
 
 
 def test_eigen_ref_life_support():
@@ -589,12 +645,9 @@ def test_eigen_ref_life_support():
 
 
 def test_special_matrix_objects():
-    assert np.all(m.incr_diag(7) == np.diag([1., 2, 3, 4, 5, 6, 7]))
+    assert np.all(m.incr_diag(7) == np.diag([1.0, 2, 3, 4, 5, 6, 7]))
 
-    asymm = np.array([[ 1.,  2,  3,  4],
-                      [ 5,  6,  7,  8],
-                      [ 9, 10, 11, 12],
-                      [13, 14, 15, 16]])
+    asymm = np.array([[1.0, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]])
     symm_lower = np.array(asymm)
     symm_upper = np.array(asymm)
     for i in range(4):
@@ -607,41 +660,51 @@ def test_special_matrix_objects():
 
 
 def test_dense_signature(doc):
-    assert doc(m.double_col) == """
+    assert (
+        doc(m.double_col)
+        == """
         double_col(arg0: numpy.ndarray[numpy.float32[m, 1]]) -> numpy.ndarray[numpy.float32[m, 1]]
     """
-    assert doc(m.double_row) == """
+    )
+    assert (
+        doc(m.double_row)
+        == """
         double_row(arg0: numpy.ndarray[numpy.float32[1, n]]) -> numpy.ndarray[numpy.float32[1, n]]
     """
-    assert doc(m.double_complex) == ("""
+    )
+    assert doc(m.double_complex) == (
+        """
         double_complex(arg0: numpy.ndarray[numpy.complex64[m, 1]])"""
-                                     """ -> numpy.ndarray[numpy.complex64[m, 1]]
-    """)
-    assert doc(m.double_mat_rm) == ("""
+        """ -> numpy.ndarray[numpy.complex64[m, 1]]
+    """
+    )
+    assert doc(m.double_mat_rm) == (
+        """
         double_mat_rm(arg0: numpy.ndarray[numpy.float32[m, n]])"""
-                                    """ -> numpy.ndarray[numpy.float32[m, n]]
-    """)
+        """ -> numpy.ndarray[numpy.float32[m, n]]
+    """
+    )
 
 
 def test_named_arguments():
     a = np.array([[1.0, 2], [3, 4], [5, 6]])
     b = np.ones((2, 1))
 
-    assert np.all(m.matrix_multiply(a, b) == np.array([[3.], [7], [11]]))
-    assert np.all(m.matrix_multiply(A=a, B=b) == np.array([[3.], [7], [11]]))
-    assert np.all(m.matrix_multiply(B=b, A=a) == np.array([[3.], [7], [11]]))
+    assert np.all(m.matrix_multiply(a, b) == np.array([[3.0], [7], [11]]))
+    assert np.all(m.matrix_multiply(A=a, B=b) == np.array([[3.0], [7], [11]]))
+    assert np.all(m.matrix_multiply(B=b, A=a) == np.array([[3.0], [7], [11]]))
 
     with pytest.raises(ValueError) as excinfo:
         m.matrix_multiply(b, a)
-    assert str(excinfo.value) == 'Nonconformable matrices!'
+    assert str(excinfo.value) == "Nonconformable matrices!"
 
     with pytest.raises(ValueError) as excinfo:
         m.matrix_multiply(A=b, B=a)
-    assert str(excinfo.value) == 'Nonconformable matrices!'
+    assert str(excinfo.value) == "Nonconformable matrices!"
 
     with pytest.raises(ValueError) as excinfo:
         m.matrix_multiply(B=a, A=b)
-    assert str(excinfo.value) == 'Nonconformable matrices!'
+    assert str(excinfo.value) == "Nonconformable matrices!"
 
 
 def test_sparse():
@@ -656,21 +719,31 @@ def test_sparse():
 
 def test_sparse_signature(doc):
     pytest.importorskip("scipy")
-    assert doc(m.sparse_copy_r) == """
+    assert (
+        doc(m.sparse_copy_r)
+        == """
         sparse_copy_r(arg0: scipy.sparse.csr_matrix[numpy.float32]) -> scipy.sparse.csr_matrix[numpy.float32]
     """  # noqa: E501 line too long
-    assert doc(m.sparse_copy_c) == """
+    )
+    assert (
+        doc(m.sparse_copy_c)
+        == """
         sparse_copy_c(arg0: scipy.sparse.csc_matrix[numpy.float32]) -> scipy.sparse.csc_matrix[numpy.float32]
     """  # noqa: E501 line too long
+    )
 
 
 def test_issue738():
     """Ignore strides on a length-1 dimension (even if they would be incompatible length > 1)"""
-    assert np.all(m.iss738_f1(np.array([[1., 2, 3]])) == np.array([[1., 102, 203]]))
-    assert np.all(m.iss738_f1(np.array([[1.], [2], [3]])) == np.array([[1.], [12], [23]]))
-
-    assert np.all(m.iss738_f2(np.array([[1., 2, 3]])) == np.array([[1., 102, 203]]))
-    assert np.all(m.iss738_f2(np.array([[1.], [2], [3]])) == np.array([[1.], [12], [23]]))
+    assert np.all(m.iss738_f1(np.array([[1.0, 2, 3]])) == np.array([[1.0, 102, 203]]))
+    assert np.all(
+        m.iss738_f1(np.array([[1.0], [2], [3]])) == np.array([[1.0], [12], [23]])
+    )
+
+    assert np.all(m.iss738_f2(np.array([[1.0, 2, 3]])) == np.array([[1.0, 102, 203]]))
+    assert np.all(
+        m.iss738_f2(np.array([[1.0], [2], [3]])) == np.array([[1.0], [12], [23]])
+    )
 
 
 def test_issue1105():

tests/test_enum.py

@@ -24,18 +24,24 @@ def test_unscoped_enum():
     assert m.UnscopedEnum.EOne.name == "EOne"
 
     # __members__ property
-    assert m.UnscopedEnum.__members__ == \
-        {"EOne": m.UnscopedEnum.EOne, "ETwo": m.UnscopedEnum.ETwo, "EThree": m.UnscopedEnum.EThree}
+    assert m.UnscopedEnum.__members__ == {
+        "EOne": m.UnscopedEnum.EOne,
+        "ETwo": m.UnscopedEnum.ETwo,
+        "EThree": m.UnscopedEnum.EThree,
+    }
     # __members__ readonly
     with pytest.raises(AttributeError):
         m.UnscopedEnum.__members__ = {}
     # __members__ returns a copy
     foo = m.UnscopedEnum.__members__
     foo["bar"] = "baz"
-    assert m.UnscopedEnum.__members__ == \
-        {"EOne": m.UnscopedEnum.EOne, "ETwo": m.UnscopedEnum.ETwo, "EThree": m.UnscopedEnum.EThree}
+    assert m.UnscopedEnum.__members__ == {
+        "EOne": m.UnscopedEnum.EOne,
+        "ETwo": m.UnscopedEnum.ETwo,
+        "EThree": m.UnscopedEnum.EThree,
+    }
 
-    for docstring_line in '''An unscoped enumeration
+    for docstring_line in """An unscoped enumeration
 
 Members:
 
@@ -43,7 +49,9 @@ Members:
 
   ETwo : Docstring for ETwo
 
-  EThree : Docstring for EThree'''.split('\n'):
+  EThree : Docstring for EThree""".split(
+        "\n"
+    ):
         assert docstring_line in m.UnscopedEnum.__doc__
 
     # Unscoped enums will accept ==/!= int comparisons
@@ -53,10 +61,10 @@ Members:
     assert y != 3
     assert 3 != y
     # Compare with None
-    assert (y != None)  # noqa: E711
+    assert y != None  # noqa: E711
     assert not (y == None)  # noqa: E711
     # Compare with an object
-    assert (y != object())
+    assert y != object()
     assert not (y == object())
     # Compare with string
     assert y != "2"
@@ -119,10 +127,10 @@ def test_scoped_enum():
     assert z != 3
     assert 3 != z
     # Compare with None
-    assert (z != None)  # noqa: E711
+    assert z != None  # noqa: E711
     assert not (z == None)  # noqa: E711
     # Compare with an object
-    assert (z != object())
+    assert z != object()
     assert not (z == object())
     # Scoped enums will *NOT* accept >, <, >= and <= int comparisons (Will throw exceptions)
     with pytest.raises(TypeError):

tests/test_eval_call.py

 # -*- coding: utf-8 -*-
 # This file is called from 'test_eval.py'
 
-if 'call_test2' in locals():
+if "call_test2" in locals():
     call_test2(y)  # noqa: F821 undefined name

tests/test_exceptions.py

@@ -54,27 +54,27 @@ def test_python_alreadyset_in_destructor(monkeypatch, capsys):
     hooked = False
     triggered = [False]  # mutable, so Python 2.7 closure can modify it
 
-    if hasattr(sys, 'unraisablehook'):  # Python 3.8+
+    if hasattr(sys, "unraisablehook"):  # Python 3.8+
         hooked = True
         default_hook = sys.unraisablehook
 
         def hook(unraisable_hook_args):
             exc_type, exc_value, exc_tb, err_msg, obj = unraisable_hook_args
-            if obj == 'already_set demo':
+            if obj == "already_set demo":
                 triggered[0] = True
             default_hook(unraisable_hook_args)
             return
 
         # Use monkeypatch so pytest can apply and remove the patch as appropriate
-        monkeypatch.setattr(sys, 'unraisablehook', hook)
+        monkeypatch.setattr(sys, "unraisablehook", hook)
 
-    assert m.python_alreadyset_in_destructor('already_set demo') is True
+    assert m.python_alreadyset_in_destructor("already_set demo") is True
     if hooked:
         assert triggered[0] is True
 
     _, captured_stderr = capsys.readouterr()
     # Error message is different in Python 2 and 3, check for words that appear in both
-    assert 'ignored' in captured_stderr and 'already_set demo' in captured_stderr
+    assert "ignored" in captured_stderr and "already_set demo" in captured_stderr
 
 
 def test_exception_matches():
@@ -107,7 +107,9 @@ def test_custom(msg):
     # Can we fall-through to the default handler?
     with pytest.raises(RuntimeError) as excinfo:
         m.throws_logic_error()
-    assert msg(excinfo.value) == "this error should fall through to the standard handler"
+    assert (
+        msg(excinfo.value) == "this error should fall through to the standard handler"
+    )
 
     # OverFlow error translation.
     with pytest.raises(OverflowError) as excinfo:
@@ -166,7 +168,13 @@ def test_nested_throws(capture):
     # C++ -> Python -> C++ -> Python
     with capture:
         m.try_catch(
-            m.MyException5, pycatch, m.MyException, m.try_catch, m.MyException, throw_myex5)
+            m.MyException5,
+            pycatch,
+            m.MyException,
+            m.try_catch,
+            m.MyException,
+            throw_myex5,
+        )
     assert str(capture).startswith("MyException5: nested error 5")
 
     # C++ -> Python -> C++
@@ -182,7 +190,6 @@ def test_nested_throws(capture):
 
 # This can often happen if you wrap a pybind11 class in a Python wrapper
 def test_invalid_repr():
-
     class MyRepr(object):
         def __repr__(self):
             raise AttributeError("Example error")

tests/test_factory_constructors.py

@@ -12,7 +12,10 @@ from pybind11_tests import ConstructorStats
 def test_init_factory_basic():
     """Tests py::init_factory() wrapper around various ways of returning the object"""
 
-    cstats = [ConstructorStats.get(c) for c in [m.TestFactory1, m.TestFactory2, m.TestFactory3]]
+    cstats = [
+        ConstructorStats.get(c)
+        for c in [m.TestFactory1, m.TestFactory2, m.TestFactory3]
+    ]
     cstats[0].alive()  # force gc
     n_inst = ConstructorStats.detail_reg_inst()
 
@@ -41,12 +44,12 @@ def test_init_factory_basic():
     z3 = m.TestFactory3("bye")
     assert z3.value == "bye"
 
-    for null_ptr_kind in [tag.null_ptr,
-                          tag.null_unique_ptr,
-                          tag.null_shared_ptr]:
+    for null_ptr_kind in [tag.null_ptr, tag.null_unique_ptr, tag.null_shared_ptr]:
         with pytest.raises(TypeError) as excinfo:
             m.TestFactory3(null_ptr_kind)
-        assert str(excinfo.value) == "pybind11::init(): factory function returned nullptr"
+        assert (
+            str(excinfo.value) == "pybind11::init(): factory function returned nullptr"
+        )
 
     assert [i.alive() for i in cstats] == [3, 3, 3]
     assert ConstructorStats.detail_reg_inst() == n_inst + 9
@@ -61,7 +64,7 @@ def test_init_factory_basic():
     assert [i.values() for i in cstats] == [
         ["3", "hi!"],
         ["7", "hi again"],
-        ["42", "bye"]
+        ["42", "bye"],
     ]
     assert [i.default_constructions for i in cstats] == [1, 1, 1]
 
@@ -69,7 +72,9 @@ def test_init_factory_basic():
 def test_init_factory_signature(msg):
     with pytest.raises(TypeError) as excinfo:
         m.TestFactory1("invalid", "constructor", "arguments")
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         __init__(): incompatible constructor arguments. The following argument types are supported:
             1. m.factory_constructors.TestFactory1(arg0: m.factory_constructors.tag.unique_ptr_tag, arg1: int)
             2. m.factory_constructors.TestFactory1(arg0: str)
@@ -78,8 +83,11 @@ def test_init_factory_signature(msg):
 
         Invoked with: 'invalid', 'constructor', 'arguments'
     """  # noqa: E501 line too long
+    )
 
-    assert msg(m.TestFactory1.__init__.__doc__) == """
+    assert (
+        msg(m.TestFactory1.__init__.__doc__)
+        == """
         __init__(*args, **kwargs)
         Overloaded function.
 
@@ -91,12 +99,16 @@ def test_init_factory_signature(msg):
 
         4. __init__(self: m.factory_constructors.TestFactory1, arg0: handle, arg1: int, arg2: handle) -> None
     """  # noqa: E501 line too long
+    )
 
 
 def test_init_factory_casting():
     """Tests py::init_factory() wrapper with various upcasting and downcasting returns"""
 
-    cstats = [ConstructorStats.get(c) for c in [m.TestFactory3, m.TestFactory4, m.TestFactory5]]
+    cstats = [
+        ConstructorStats.get(c)
+        for c in [m.TestFactory3, m.TestFactory4, m.TestFactory5]
+    ]
     cstats[0].alive()  # force gc
     n_inst = ConstructorStats.detail_reg_inst()
 
@@ -134,7 +146,7 @@ def test_init_factory_casting():
     assert [i.values() for i in cstats] == [
         ["4", "5", "6", "7", "8"],
         ["4", "5", "8"],
-        ["6", "7"]
+        ["6", "7"],
     ]
 
 
@@ -204,7 +216,7 @@ def test_init_factory_alias():
 
     assert [i.values() for i in cstats] == [
         ["1", "8", "3", "4", "5", "6", "123", "10", "47"],
-        ["hi there", "3", "4", "6", "move", "123", "why hello!", "move", "47"]
+        ["hi there", "3", "4", "6", "move", "123", "why hello!", "move", "47"],
     ]
 
 
@@ -268,9 +280,11 @@ def test_init_factory_dual():
     assert not g1.has_alias()
     with pytest.raises(TypeError) as excinfo:
         PythFactory7(tag.shared_ptr, tag.invalid_base, 14)
-    assert (str(excinfo.value) ==
-            "pybind11::init(): construction failed: returned holder-wrapped instance is not an "
-            "alias instance")
+    assert (
+        str(excinfo.value)
+        == "pybind11::init(): construction failed: returned holder-wrapped instance is not an "
+        "alias instance"
+    )
 
     assert [i.alive() for i in cstats] == [13, 7]
     assert ConstructorStats.detail_reg_inst() == n_inst + 13
@@ -284,7 +298,7 @@ def test_init_factory_dual():
 
     assert [i.values() for i in cstats] == [
         ["1", "2", "3", "4", "5", "6", "7", "8", "9", "100", "11", "12", "13", "14"],
-        ["2", "4", "6", "8", "9", "100", "12"]
+        ["2", "4", "6", "8", "9", "100", "12"],
     ]
 
 
@@ -294,7 +308,7 @@ def test_no_placement_new(capture):
     with capture:
         a = m.NoPlacementNew(123)
 
-    found = re.search(r'^operator new called, returning (\d+)\n$', str(capture))
+    found = re.search(r"^operator new called, returning (\d+)\n$", str(capture))
     assert found
     assert a.i == 123
     with capture:
@@ -305,7 +319,7 @@ def test_no_placement_new(capture):
     with capture:
         b = m.NoPlacementNew()
 
-    found = re.search(r'^operator new called, returning (\d+)\n$', str(capture))
+    found = re.search(r"^operator new called, returning (\d+)\n$", str(capture))
     assert found
     assert b.i == 100
     with capture:
@@ -333,7 +347,7 @@ def create_and_destroy(*args):
 
 
 def strip_comments(s):
-    return re.sub(r'\s+#.*', '', s)
+    return re.sub(r"\s+#.*", "", s)
 
 
 def test_reallocation_a(capture, msg):
@@ -345,7 +359,9 @@ def test_reallocation_a(capture, msg):
 
     with capture:
         create_and_destroy(1)
-    assert msg(capture) == """
+    assert (
+        msg(capture)
+        == """
         noisy new
         noisy placement new
         NoisyAlloc(int 1)
@@ -353,12 +369,14 @@ def test_reallocation_a(capture, msg):
         ~NoisyAlloc()
         noisy delete
     """
+    )
 
 
 def test_reallocation_b(capture, msg):
     with capture:
         create_and_destroy(1.5)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new               # allocation required to attempt first overload
         noisy delete            # have to dealloc before considering factory init overload
         noisy new               # pointer factory calling "new", part 1: allocation
@@ -366,51 +384,59 @@ def test_reallocation_b(capture, msg):
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_c(capture, msg):
     with capture:
         create_and_destroy(2, 3)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new          # pointer factory calling "new", allocation
         NoisyAlloc(int 2)  # constructor
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_d(capture, msg):
     with capture:
         create_and_destroy(2.5, 3)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         NoisyAlloc(double 2.5)  # construction (local func variable: operator_new not called)
         noisy new               # return-by-value "new" part 1: allocation
         ~NoisyAlloc()           # moved-away local func variable destruction
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_e(capture, msg):
     with capture:
         create_and_destroy(3.5, 4.5)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new               # preallocation needed before invoking placement-new overload
         noisy placement new     # Placement new
         NoisyAlloc(double 3.5)  # construction
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_f(capture, msg):
     with capture:
         create_and_destroy(4, 0.5)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new          # preallocation needed before invoking placement-new overload
         noisy delete       # deallocation of preallocated storage
         noisy new          # Factory pointer allocation
@@ -418,13 +444,15 @@ def test_reallocation_f(capture, msg):
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_g(capture, msg):
     with capture:
         create_and_destroy(5, "hi")
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new            # preallocation needed before invoking first placement new
         noisy delete         # delete before considering new-style constructor
         noisy new            # preallocation for second placement new
@@ -433,13 +461,15 @@ def test_reallocation_g(capture, msg):
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 @pytest.mark.skipif("env.PY2")
 def test_invalid_self():
     """Tests invocation of the pybind-registered base class with an invalid `self` argument.  You
     can only actually do this on Python 3: Python 2 raises an exception itself if you try."""
+
     class NotPybindDerived(object):
         pass
 
@@ -463,16 +493,26 @@ def test_invalid_self():
                 a = m.TestFactory2(tag.pointer, 1)
                 m.TestFactory6.__init__(a, tag.alias, 1)
             elif bad == 3:
-                m.TestFactory6.__init__(NotPybindDerived.__new__(NotPybindDerived), tag.base, 1)
+                m.TestFactory6.__init__(
+                    NotPybindDerived.__new__(NotPybindDerived), tag.base, 1
+                )
             elif bad == 4:
-                m.TestFactory6.__init__(NotPybindDerived.__new__(NotPybindDerived), tag.alias, 1)
+                m.TestFactory6.__init__(
+                    NotPybindDerived.__new__(NotPybindDerived), tag.alias, 1
+                )
 
     for arg in (1, 2):
         with pytest.raises(TypeError) as excinfo:
             BrokenTF1(arg)
-        assert str(excinfo.value) == "__init__(self, ...) called with invalid `self` argument"
+        assert (
+            str(excinfo.value)
+            == "__init__(self, ...) called with invalid `self` argument"
+        )
 
     for arg in (1, 2, 3, 4):
         with pytest.raises(TypeError) as excinfo:
             BrokenTF6(arg)
-        assert str(excinfo.value) == "__init__(self, ...) called with invalid `self` argument"
+        assert (
+            str(excinfo.value)
+            == "__init__(self, ...) called with invalid `self` argument"
+        )

tests/test_gil_scoped.py

@@ -21,6 +21,7 @@ def _run_in_process(target, *args, **kwargs):
 
 def _python_to_cpp_to_python():
     """Calls different C++ functions that come back to Python."""
+
     class ExtendedVirtClass(m.VirtClass):
         def virtual_func(self):
             pass
@@ -74,7 +75,9 @@ def test_python_to_cpp_to_python_from_thread_multiple_sequential():
 
     It runs in a separate process to be able to stop and assert if it deadlocks.
     """
-    assert _run_in_process(_python_to_cpp_to_python_from_threads, 8, parallel=False) == 0
+    assert (
+        _run_in_process(_python_to_cpp_to_python_from_threads, 8, parallel=False) == 0
+    )
 
 
 # TODO: FIXME on macOS Python 3.9

tests/test_iostream.py

@@ -18,6 +18,7 @@ try:
     # Python 3.4
     from contextlib import redirect_stdout
 except ImportError:
+
     @contextmanager
     def redirect_stdout(target):
         original = sys.stdout
@@ -25,10 +26,12 @@ except ImportError:
         yield
         sys.stdout = original
 
+
 try:
     # Python 3.5
     from contextlib import redirect_stderr
 except ImportError:
+
     @contextmanager
     def redirect_stderr(target):
         original = sys.stderr
@@ -42,16 +45,16 @@ def test_captured(capsys):
     m.captured_output(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
 
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
 
     m.captured_err(msg)
     stdout, stderr = capsys.readouterr()
-    assert stdout == ''
+    assert stdout == ""
     assert stderr == msg
 
 
@@ -63,7 +66,7 @@ def test_captured_large_string(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
 
 
 def test_guard_capture(capsys):
@@ -71,7 +74,7 @@ def test_guard_capture(capsys):
     m.guard_output(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
 
 
 def test_series_captured(capture):
@@ -88,7 +91,7 @@ def test_flush(capfd):
     with m.ostream_redirect():
         m.noisy_function(msg, flush=False)
         stdout, stderr = capfd.readouterr()
-        assert stdout == ''
+        assert stdout == ""
 
         m.noisy_function(msg2, flush=True)
         stdout, stderr = capfd.readouterr()
@@ -107,15 +110,15 @@ def test_not_captured(capfd):
         m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stderr == ''
-    assert stream.getvalue() == ''
+    assert stderr == ""
+    assert stream.getvalue() == ""
 
     stream = StringIO()
     with redirect_stdout(stream):
         m.captured_output(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
-    assert stderr == ''
+    assert stdout == ""
+    assert stderr == ""
     assert stream.getvalue() == msg
 
 
@@ -125,16 +128,16 @@ def test_err(capfd):
     with redirect_stderr(stream):
         m.raw_err(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
+    assert stdout == ""
     assert stderr == msg
-    assert stream.getvalue() == ''
+    assert stream.getvalue() == ""
 
     stream = StringIO()
     with redirect_stderr(stream):
         m.captured_err(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
-    assert stderr == ''
+    assert stdout == ""
+    assert stderr == ""
     assert stream.getvalue() == msg
 
 
@@ -146,8 +149,8 @@ def test_multi_captured(capfd):
         m.captured_output("c")
         m.raw_output("d")
     stdout, stderr = capfd.readouterr()
-    assert stdout == 'bd'
-    assert stream.getvalue() == 'ac'
+    assert stdout == "bd"
+    assert stream.getvalue() == "ac"
 
 
 def test_dual(capsys):
@@ -164,14 +167,14 @@ def test_redirect(capfd):
         m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stream.getvalue() == ''
+    assert stream.getvalue() == ""
 
     stream = StringIO()
     with redirect_stdout(stream):
         with m.ostream_redirect():
             m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
+    assert stdout == ""
     assert stream.getvalue() == msg
 
     stream = StringIO()
@@ -179,7 +182,7 @@ def test_redirect(capfd):
         m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stream.getvalue() == ''
+    assert stream.getvalue() == ""
 
 
 def test_redirect_err(capfd):
@@ -193,7 +196,7 @@ def test_redirect_err(capfd):
             m.raw_err(msg2)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
     assert stream.getvalue() == msg2
 
 
@@ -209,7 +212,7 @@ def test_redirect_both(capfd):
                 m.raw_output(msg)
                 m.raw_err(msg2)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
-    assert stderr == ''
+    assert stdout == ""
+    assert stderr == ""
     assert stream.getvalue() == msg
     assert stream2.getvalue() == msg2