Issue #28192: Don't import readline in isolated mode
diff --git a/Lib/site.py b/Lib/site.py
index 5250266..b637635 100644
--- a/Lib/site.py
+++ b/Lib/site.py
@@ -60,7 +60,8 @@
 
 The readline module is also automatically configured to enable
 completion for systems that support it.  This can be overridden in
-sitecustomize, usercustomize or PYTHONSTARTUP.
+sitecustomize, usercustomize or PYTHONSTARTUP.  Starting Python in
+isolated mode (-I) disables automatic readline configuration.
 
 After these operations, an attempt is made to import a module
 named sitecustomize, which can perform arbitrary additional
@@ -491,7 +492,7 @@
             else:
                 raise
     except Exception as err:
-        if os.environ.get("PYTHONVERBOSE"):
+        if sys.flags.verbose:
             sys.excepthook(*sys.exc_info())
         else:
             sys.stderr.write(
@@ -511,7 +512,7 @@
             else:
                 raise
     except Exception as err:
-        if os.environ.get("PYTHONVERBOSE"):
+        if sys.flags.verbose:
             sys.excepthook(*sys.exc_info())
         else:
             sys.stderr.write(
@@ -538,12 +539,13 @@
     setquit()
     setcopyright()
     sethelper()
-    enablerlcompleter()
+    if not sys.flags.isolated:
+        enablerlcompleter()
     execsitecustomize()
     if ENABLE_USER_SITE:
         execusercustomize()
 
-# Prevent edition of sys.path when python was started with -S and
+# Prevent extending of sys.path when python was started with -S and
 # site is imported later.
 if not sys.flags.no_site:
     main()