Run Python commands in tox in isolated and strict mode

tox.ini

@@ -12,15 +12,23 @@ minversion = 3.14.0
 deps =
   -rrequirements/tests.in
 commands_pre =
-  {envpython} -m \
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -m \
     OpenSSL.debug
 commands =
-  {envpython} -m \
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -m \
     pytest \
     {tty:--color=yes} \
     {posargs:}
 install_command =
   {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
     {toxinidir}/bin/pip-wrapper \
     '{envname}' \
     '{toxinidir}/requirements/' \
@@ -48,6 +56,14 @@ setenv =
   WEBTEST_INTERACTIVE=false
 
 
+[python-cli-options]
+byteerrors = -bb
+bytewarnings = -b
+# isolate = -I
+# FIXME: Python 2 shim. Is this equivalent to the above?
+isolate = -E -s
+
+
 [dists]
 setenv =
   PIP_CONSTRAINT = {toxinidir}/requirements/dist-build-constraints.txt
@@ -71,7 +87,10 @@ commands =
   # FIXME: instead of `{toxworkdir}/.tmp` that was added in tox v3.16.1.
   # NOTE: The last tox supporting Python 3.4 is 3.14.0
   # -d "{temp_dir}/.doctrees" \
-  {envpython} -m sphinx \
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -m sphinx \
     -j auto \
     -b html \
     {tty:--color} \
@@ -83,7 +102,10 @@ commands =
     "{envdir}/docs_out"
 
   # Print out the output docs dir and a way to serve html:
-  -{envpython} -c\
+  -{envpython} \
+  {[python-cli-options]byteerrors} \
+  {[python-cli-options]isolate} \
+  -c\
   'import pathlib;\
   docs_dir = pathlib.Path(r"{envdir}") / "docs_out";\
   index_file = docs_dir / "index.html";\
@@ -106,8 +128,11 @@ commands =
   -git fetch --unshallow
   -git fetch --tags
 
-  # Spellcheck docs site:
-  python -m sphinx \
+  # Doctest docs site:
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -m sphinx \
     -j auto \
     -a -n -W \
     --keep-going \
@@ -129,8 +154,11 @@ commands =
   -git fetch --unshallow
   -git fetch --tags
 
-  # Spellcheck docs site:
-  python -m sphinx \
+  # Linkcheck docs site:
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -m sphinx \
     -j auto \
     -a -n -W \
     --keep-going \
@@ -153,7 +181,10 @@ commands =
   -git fetch --tags
 
   # Spellcheck docs site:
-  python -m sphinx \
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -m sphinx \
     -j auto \
     -a -n -W \
     --keep-going \
@@ -179,8 +210,14 @@ deps =
 usedevelop = False
 commands_pre =
 commands =
-  python -m twine check .tox/dist/*
-  python -m setuptools_scm ls
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -m twine check .tox/dist/*
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -m setuptools_scm ls
 
 
 [testenv:cleanup-dists]
@@ -193,7 +230,10 @@ setenv =
   {[dists]setenv}
 commands_pre =
 commands =
-  {envpython} -c \
+  {envpython} \
+  {[python-cli-options]byteerrors} \
+  {[python-cli-options]isolate} \
+  -c \
     'import os, shutil, sys; dists_dir = os.getenv("PEP517_OUT_DIR"); shutil.rmtree(dists_dir, ignore_errors=True); sys.exit(os.path.exists(dists_dir))'
 
 
@@ -211,6 +251,8 @@ platform = darwin|linux
 install_command =
   env PIP_CONSTRAINT= \
     {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
     {toxinidir}/bin/pip-wrapper \
     '{envname}' \
     '{toxinidir}/requirements/' \
@@ -231,7 +273,10 @@ commands =
   # if no format arguments are passed. This makes sure that
   # wheels are not dependent on the Git repo or anything
   # external what may be missing from sdist.
-  {envpython} -m build \
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -m build \
     --outdir '{env:PEP517_OUT_DIR}/' \
     {posargs:{env:PEP517_BUILD_ARGS:}} \
     '{toxinidir}'
@@ -251,7 +296,10 @@ commands_pre =
 setenv =
   {[dists]setenv}
 commands =
-  {envpython} -m twine check \
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate}
+    -m twine check \
     --strict \
     {env:PEP517_OUT_DIR}/*
 
@@ -267,6 +315,13 @@ setenv =
   TWINE_USERNAME = {env:TWINE_USERNAME:__token__}
 commands_pre =
 commands =
-  python -c "import path; path.Path('dist').rmtree_p()"
-  python -m pep517.build .
-  python -m twine upload dist/*
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} \
+    -c "import path; path.Path('dist').rmtree_p()"
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} -m pep517.build .
+  {envpython} \
+    {[python-cli-options]byteerrors} \
+    {[python-cli-options]isolate} -m twine upload dist/*