gh-98251: Allow venv to pass along PYTHON* variables to pip when they do not impact path resolution

Lib/test/test_venv.py

@@ -216,7 +216,7 @@ def test_upgrade_dependencies(self):
  if sys.platform == 'win32':
  expect_exe = os.path.normcase(os.path.realpath(expect_exe))
 
- def pip_cmd_checker(cmd):
+ def pip_cmd_checker(cmd, **kwargs):
  cmd[0] = os.path.normcase(cmd[0])
  self.assertEqual(
  cmd,
@@ -232,7 +232,7 @@ def pip_cmd_checker(cmd):
  )
 
  fake_context = builder.ensure_directories(fake_env_dir)
- with patch('venv.subprocess.check_call', pip_cmd_checker):
+ with patch('venv.subprocess.check_output', pip_cmd_checker):
  builder.upgrade_dependencies(fake_context)
 
  @requireVenvCreate
@@ -659,8 +659,8 @@ def nicer_error(self):
  try:
  yield
  except subprocess.CalledProcessError as exc:
- out = exc.output.decode(errors="replace")
- err = exc.stderr.decode(errors="replace")
+ out = (exc.output or b'').decode(errors="replace")
+ err = (exc.stderr or b'').decode(errors="replace")
  self.fail(
  f"{exc}\n\n"
  f"**Subprocess Output**\n{out}\n\n"

Lib/venv/__init__.py

@@ -339,14 +339,25 @@ def setup_python(self, context):
  shutil.copyfile(src, dst)
  break
 
+ def _call_new_python(self, context, *py_args, **kwargs):
+ """Executes the newly created Python using safe-ish options"""
+ # gh-98251: We do not want to just use '-I' because that masks
+ # legitimate user preferences (such as not writing bytecode). All we
+ # really need is to ensure that the path variables do not overrule
+ # normal venv handling.
+ args = [context.env_exec_cmd, *py_args]
+ kwargs['env'] = env = os.environ.copy()
+ env['VIRTUAL_ENV'] = context.env_dir
+ env.pop('PYTHONHOME', None)
+ env.pop('PYTHONPATH', None)
+ kwargs['cwd'] = context.env_dir
+ kwargs['executable'] = context.env_exec_cmd
+ subprocess.check_output(args, **kwargs)
+
  def _setup_pip(self, context):
  """Installs or upgrades pip in a virtual environment"""
- # We run ensurepip in isolated mode to avoid side effects from
- # environment vars, the current directory and anything else
- # intended for the global Python environment
- cmd = [context.env_exec_cmd, '-Im', 'ensurepip', '--upgrade',
- '--default-pip']
- subprocess.check_output(cmd, stderr=subprocess.STDOUT)
+ self._call_new_python(context, '-m', 'ensurepip', '--upgrade',
+ '--default-pip', stderr=subprocess.STDOUT)
 
  def setup_scripts(self, context):
  """
@@ -445,9 +456,8 @@ def upgrade_dependencies(self, context):
  logger.debug(
  f'Upgrading {CORE_VENV_DEPS} packages in {context.bin_path}'
  )
- cmd = [context.env_exec_cmd, '-m', 'pip', 'install', '--upgrade']
- cmd.extend(CORE_VENV_DEPS)
- subprocess.check_call(cmd)
+ self._call_new_python(context, '-m', 'pip', 'install', '--upgrade',
+ *CORE_VENV_DEPS)
 
 
 def create(env_dir, system_site_packages=False, clear=False,

Misc/NEWS.d/next/Library/2022-10-14-11-46-31.gh-issue-98251.Uxc9al.rst

@@ -0,0 +1,2 @@
+Allow :mod:`venv` to pass along :envvar:`PYTHON*` variables to ``ensurepip`` and ``pip`` when
+they do not impact path resolution