pythonGH-139809: Fix argparse subcommand prog not respecting color environment variables (python#139818)

Author: savannahostrowski

Lib/argparse.py

@@ -1959,7 +1959,9 @@ def add_subparsers(self, **kwargs):
         # prog defaults to the usage message of this parser, skipping
         # optional arguments and with no "usage:" prefix
         if kwargs.get('prog') is None:
-            formatter = self._get_formatter()
+            # Create formatter without color to avoid storing ANSI codes in prog
+            formatter = self.formatter_class(prog=self.prog)
+            formatter._set_color(False)
             positionals = self._get_positional_actions()
             groups = self._mutually_exclusive_groups
             formatter.add_usage(None, positionals, groups, '')

Lib/test/test_argparse.py

@@ -22,6 +22,7 @@
     captured_stderr,
     force_not_colorized,
     force_not_colorized_test_class,
+    swap_attr,
 )
 from test.support import import_helper
 from test.support import os_helper
@@ -7128,7 +7129,8 @@ class TestColorized(TestCase):
     def setUp(self):
         super().setUp()
         # Ensure color even if ran with NO_COLOR=1
-        _colorize.can_colorize = lambda *args, **kwargs: True
+        self.enterContext(swap_attr(_colorize, 'can_colorize',
+                                     lambda *args, **kwargs: True))
         self.theme = _colorize.get_theme(force_color=True).argparse
 
     def test_argparse_color(self):
@@ -7355,6 +7357,17 @@ def __init__(self, prog):
                  {short_b}+f{reset}, {long_b}++foo{reset} {label_b}FOO{reset}  foo help
         '''))
 
+    def test_subparser_prog_is_stored_without_color(self):
+        parser = argparse.ArgumentParser(prog='complex', color=True)
+        sub = parser.add_subparsers(dest='command')
+        demo_parser = sub.add_parser('demo')
+
+        self.assertNotIn('\x1b[', demo_parser.prog)
+
+        demo_parser.color = False
+        help_text = demo_parser.format_help()
+        self.assertNotIn('\x1b[', help_text)
+
 
 class TestModule(unittest.TestCase):
     def test_deprecated__version__(self):

Misc/NEWS.d/next/Library/2025-10-09-03-06-19.gh-issue-139809.lzHJNu.rst

@@ -0,0 +1 @@
+Prevent premature colorization of subparser ``prog`` in :meth:`argparse.ArgumentParser.add_subparsers` to respect color environment variable changes after parser creation.