[3.10] pythongh-96861: Check for unset sys.executable during venv cre…

…ation. (pythonGH-96887) (pythonGH-96918)

(cherry picked from commit 2cd70ff)

Co-authored-by: Vinay Sajip <vinay_sajip@yahoo.co.uk>

Co-authored-by: Vinay Sajip <vinay_sajip@yahoo.co.uk>

Lib/venv/__init__.py

@@ -115,6 +115,11 @@ def create_if_needed(d):
         context.prompt = '(%s) ' % prompt
         create_if_needed(env_dir)
         executable = sys._base_executable
+        if not executable:  # see gh-96861
+            raise ValueError('Unable to determine path to the running '
+                             'Python interpreter. Provide an explicit path or '
+                             'check that your PATH environment variable is '
+                             'correctly set.')
         dirname, exename = os.path.split(os.path.abspath(executable))
         context.executable = executable
         context.python_dir = dirname