diff --git a/nbconvert/exporters/html.py b/nbconvert/exporters/html.py
index b56a2c24f..bee8a8968 100644
--- a/nbconvert/exporters/html.py
+++ b/nbconvert/exporters/html.py
@@ -5,7 +5,6 @@
 
 import base64
 import json
-from lxml.html.clean import clean_html
 import mimetypes
 import os
 from pathlib import Path
diff --git a/nbconvert/exporters/templateexporter.py b/nbconvert/exporters/templateexporter.py
index 4f8a03e88..e0c60ef36 100644
--- a/nbconvert/exporters/templateexporter.py
+++ b/nbconvert/exporters/templateexporter.py
@@ -6,9 +6,8 @@
 # Distributed under the terms of the Modified BSD License.
 
 
-import json
 import html
-from lxml.html.clean import clean_html
+import json
 import os
 import uuid
 import warnings
@@ -23,6 +22,7 @@
     TemplateNotFound,
 )
 from jupyter_core.paths import jupyter_path
+from lxml.html.clean import clean_html
 from traitlets import Bool, Dict, HasTraits, List, Unicode, default, observe, validate
 from traitlets.config import Config
 from traitlets.utils.importstring import import_item
diff --git a/nbconvert/exporters/tests/test_html.py b/nbconvert/exporters/tests/test_html.py
index 6a43c709d..56c4dec25 100644
--- a/nbconvert/exporters/tests/test_html.py
+++ b/nbconvert/exporters/tests/test_html.py
@@ -137,9 +137,9 @@ def test_basic_name(self):
 
     def test_javascript_injection(self):
         for template in ["lab", "classic", "reveal"]:
-            (output, resources) = HTMLExporter(
-                template_name=template
-            ).from_filename(self._get_notebook('notebook_inject.ipynb'))
+            (output, resources) = HTMLExporter(template_name=template).from_filename(
+                self._get_notebook("notebook_inject.ipynb")
+            )
 
             # Check injection in the metadata.title of the Notebook
             assert "<script>alert('title')</script>" not in output
@@ -170,14 +170,17 @@ def test_javascript_injection(self):
             assert "<script>alert('output.metadata.height png injection')</script>" not in output
 
             # Check injection in widget view
-            assert "<script>alert('output.data.application/vnd.jupyter.widget-view+json injection')" not in output
+            assert (
+                "<script>alert('output.data.application/vnd.jupyter.widget-view+json injection')"
+                not in output
+            )
 
         # By design, text/html, text/markdown, application/javascript and markdown cells should allow
         # for JavaScript code execution
         for template in ["lab", "classic", "reveal"]:
-            (output, resources) = HTMLExporter(
-                template_name=template
-            ).from_filename(self._get_notebook('notebook_inject.ipynb'))
+            (output, resources) = HTMLExporter(template_name=template).from_filename(
+                self._get_notebook("notebook_inject.ipynb")
+            )
 
             assert "<script>alert('markdown cell')</script>" in output
             assert "<script>alert('text/markdown output')</script>" in output
@@ -187,9 +190,8 @@ def test_javascript_injection(self):
         # But it's an opt-out
         for template in ["lab", "classic", "reveal"]:
             (output, resources) = HTMLExporter(
-                template_name=template,
-                sanitize_html=True
-            ).from_filename(self._get_notebook('notebook_inject.ipynb'))
+                template_name=template, sanitize_html=True
+            ).from_filename(self._get_notebook("notebook_inject.ipynb"))
 
             assert "<script>alert('markdown cell')</script>" not in output
             assert "<script>alert('text/markdown output')</script>" not in output
diff --git a/nbconvert/filters/highlight.py b/nbconvert/filters/highlight.py
index e48946df5..40ed574df 100644
--- a/nbconvert/filters/highlight.py
+++ b/nbconvert/filters/highlight.py
@@ -68,7 +68,9 @@ def __call__(self, source, language=None, metadata=None):
         return _pygments_highlight(
             source if len(source) > 0 else " ",
             # needed to help post processors:
-            HtmlFormatter(cssclass=escape(f" highlight hl-{language}"), **self.extra_formatter_options),
+            HtmlFormatter(
+                cssclass=escape(f" highlight hl-{language}"), **self.extra_formatter_options
+            ),
             language,
             metadata,
         )
diff --git a/nbconvert/filters/tests/test_highlight.py b/nbconvert/filters/tests/test_highlight.py
index da224323f..08c734460 100644
--- a/nbconvert/filters/tests/test_highlight.py
+++ b/nbconvert/filters/tests/test_highlight.py
@@ -77,7 +77,7 @@ def test_parse_html_many_lang(self):
     @pytest.mark.filterwarnings("ignore")
     def test_inject_html(self):
         out = highlight2html(self.tests[0], 'ipython3-foo"><script>alert(1)</script>')
-        assert '<script>alert(1)</script>' not in out
+        assert "<script>alert(1)</script>" not in out
 
     def _extract_tokens(self, root, cls):
         return set(map(lambda x: x.text, root.findall(".//*[@class='" + cls + "']")))
diff --git a/nbconvert/tests/test_nbconvertapp.py b/nbconvert/tests/test_nbconvertapp.py
index f01466a34..d02be3d39 100644
--- a/nbconvert/tests/test_nbconvertapp.py
+++ b/nbconvert/tests/test_nbconvertapp.py
@@ -374,7 +374,7 @@ def test_no_input(self):
                     '<span class="o">=</span> '
                     '<span class="n">symbols</span>'
                     '<span class="p">(</span>'
-                    '<span class="s1">\'x y z\'</span>'
+                    "<span class=\"s1\">'x y z'</span>"
                     '<span class="p">)</span>'
                 ) not in text
             self.nbconvert("notebook1.ipynb --log-level 0 --to html")
@@ -392,7 +392,7 @@ def test_no_input(self):
                     '<span class="o">=</span> '
                     '<span class="n">symbols</span>'
                     '<span class="p">(</span>'
-                    '<span class="s1">\'x y z\'</span>'
+                    "<span class=\"s1\">'x y z'</span>"
                     '<span class="p">)</span>'
                 ) in text2