gh-136355: Deprecate -b and -bb CLI flags in 3.15

Author: sobolevn

Doc/using/cmdline.rst

@@ -254,6 +254,16 @@ Miscellaneous options
    .. versionchanged:: 3.5
       Affects also comparisons of :class:`bytes` with :class:`int`.
 
+   .. deprecated-removed:: 3.15 3.17
+
+      Deprecate :option:`-b` and :option:`-bb`
+      and schedule them for removal in Python 3.17.
+      They were mainly a transition helpers for Python2 -> Python3 era.
+      In 3.17 no :exc:`BytesWarning` won't be raised for these cases.
+      If you want to check for the same things in the future,
+      use any type-checker of your choice.
+
+
 .. option:: -B
 
    If given, Python won't try to write ``.pyc`` files on the

Doc/whatsnew/3.15.rst

@@ -206,6 +206,18 @@ module_name
 Deprecated
 ==========
 
+CLI
+---
+
+* Deprecate :option:`-b` and :option:`!-bb`
+  and schedule them for removal in Python 3.17.
+  They were mainly a transition helpers for Python2 -> Python3 era.
+  In 3.17 no :exc:`BytesWarning` won't be raised for these cases.
+  If you want to check for the same things in the future,
+  use any type-checker of your choice.
+
+  (Contributed by Nikita Sobolev in :gh:`136355`.)
+
 hashlib
 -------
 

Lib/test/test_cmd_line.py

@@ -32,6 +32,12 @@ def _kill_python_and_exit_code(p):
     return data, returncode
 
 
+b_deprecation_msg = (
+    '-b option is deprecated since Python 3.15 '
+    'and will be removed in Python 3.17'
+)
+
+
 class CmdLineTest(unittest.TestCase):
     def test_directories(self):
         assert_python_failure('.')
@@ -706,7 +712,7 @@ def run_xdev(self, *args, check_exitcode=True, xdev=True):
                               env=env)
         if check_exitcode:
             self.assertEqual(proc.returncode, 0, proc)
-        return proc.stdout.rstrip()
+        return self.maybe_remove_b_deprecation_msg(proc.stdout)
 
     @support.cpython_only
     def test_xdev(self):
@@ -789,7 +795,22 @@ def check_warnings_filters(self, cmdline_option, envvar, use_pywarning=False):
                               universal_newlines=True,
                               env=env)
         self.assertEqual(proc.returncode, 0, proc)
-        return proc.stdout.rstrip()
+        return self.maybe_remove_b_deprecation_msg(proc.stdout)
+
+    def maybe_remove_b_deprecation_msg(self, output):
+        return output.replace(b_deprecation_msg + '\n', '').rstrip()
+
+    def test_b_deprecation_msg_stderr(self):
+        for arg in ['-b', '-bb']:
+            with self.subTest(arg=arg):
+                args = (sys.executable, arg, '-c', '')
+                proc = subprocess.run(args,
+                                      stdout=subprocess.PIPE,
+                                      stderr=subprocess.PIPE,
+                                      universal_newlines=True)
+                self.assertEqual(proc.returncode, 0, proc)
+                self.assertEqual(proc.stdout, '')
+                self.assertEqual(proc.stderr.rstrip(), b_deprecation_msg)
 
     def test_warnings_filter_precedence(self):
         expected_filters = ("error::BytesWarning "

Misc/NEWS.d/next/Core_and_Builtins/2025-07-07-12-24-00.gh-issue-136355.MTcA8j.rst

@@ -0,0 +1,2 @@
+Deprecate :option:`-b` and :option:`!-bb` and schedule them
+for removal in the future versions of Python.

Python/initconfig.c

@@ -256,6 +256,7 @@ static const char usage_help[] = "\
 Options (and corresponding environment variables):\n\
 -b     : issue warnings about converting bytes/bytearray to str and comparing\n\
          bytes/bytearray with str or bytes with int. (-bb: issue errors)\n\
+         deprecated since 3.15 and will be removed in 3.17\n\
 -B     : don't write .pyc files on import; also PYTHONDONTWRITEBYTECODE=x\n\
 -c cmd : program passed in as string (terminates option list)\n\
 -d     : turn on parser debugging output (for experts only, only works on\n\
@@ -2944,6 +2945,11 @@ config_parse_cmdline(PyConfig *config, PyWideStringList *warnoptions,
             return _PyStatus_EXIT(0);
 
         case 'b':
+            if (!config->bytes_warning) {
+                fprintf(stderr,
+                        "-b option is deprecated since Python 3.15 "
+                        "and will be removed in Python 3.17\n");
+            }
             config->bytes_warning++;
             break;