gh-141679: Add colour to defaults in argparse help (#141680)

Co-authored-by: Savannah Ostrowski <savannah@python.org>

Lib/_colorize.py

@@ -168,6 +168,8 @@ class Argparse(ThemeSection):
     short_option: str = ANSIColors.BOLD_GREEN
     label: str = ANSIColors.BOLD_YELLOW
     action: str = ANSIColors.BOLD_GREEN
+    default: str = ANSIColors.GREY
+    default_value: str = ANSIColors.YELLOW
     reset: str = ANSIColors.RESET
     error: str = ANSIColors.BOLD_MAGENTA
     warning: str = ANSIColors.BOLD_YELLOW

Lib/argparse.py

@@ -748,7 +748,14 @@ class ArgumentDefaultsHelpFormatter(HelpFormatter):
             if action.default is not SUPPRESS:
                 defaulting_nargs = [OPTIONAL, ZERO_OR_MORE]
                 if action.option_strings or action.nargs in defaulting_nargs:
-                    help += _(' (default: %(default)s)')
+                    t = self._theme
+                    default_str = _(" (default: %(default)s)")
+                    prefix, suffix = default_str.split("%(default)s")
+                    help += (
+                        f" {t.default}{prefix.lstrip()}"
+                        f"{t.default_value}%(default)s"
+                        f"{t.default}{suffix}{t.reset}"
+                    )
         return help
 
 

Lib/test/test_argparse.py

@@ -7288,6 +7288,8 @@ class TestColorized(TestCase):
         short_b = self.theme.short_option
         label_b = self.theme.label
         pos_b = self.theme.action
+        default = self.theme.default
+        default_value = self.theme.default_value
         reset = self.theme.reset
 
         # Act
@@ -7314,17 +7316,17 @@ class TestColorized(TestCase):
 
                 {heading}options:{reset}
                   {short_b}-h{reset}, {long_b}--help{reset}            show this help message and exit
-                  {short_b}-v{reset}, {long_b}--verbose{reset}         more spam (default: False)
-                  {short_b}-q{reset}, {long_b}--quiet{reset}           less spam (default: False)
+                  {short_b}-v{reset}, {long_b}--verbose{reset}         more spam {default}(default: {default_value}False{default}){reset}
+                  {short_b}-q{reset}, {long_b}--quiet{reset}           less spam {default}(default: {default_value}False{default}){reset}
                   {short_b}-o{reset}, {long_b}--optional1{reset}
                   {long_b}--optional2{reset} {label_b}OPTIONAL2{reset}
-                                        pick one (default: None)
+                                        pick one {default}(default: {default_value}None{default}){reset}
                   {long_b}--optional3{reset} {label_b}{{X,Y,Z}}{reset}
-                  {long_b}--optional4{reset} {label_b}{{X,Y,Z}}{reset}   pick one (default: None)
-                  {long_b}--optional5{reset} {label_b}{{X,Y,Z}}{reset}   pick one (default: None)
-                  {long_b}--optional6{reset} {label_b}{{X,Y,Z}}{reset}   pick one (default: None)
+                  {long_b}--optional4{reset} {label_b}{{X,Y,Z}}{reset}   pick one {default}(default: {default_value}None{default}){reset}
+                  {long_b}--optional5{reset} {label_b}{{X,Y,Z}}{reset}   pick one {default}(default: {default_value}None{default}){reset}
+                  {long_b}--optional6{reset} {label_b}{{X,Y,Z}}{reset}   pick one {default}(default: {default_value}None{default}){reset}
                   {short_b}-p{reset}, {long_b}--optional7{reset} {label_b}{{Aaaaa,Bbbbb,Ccccc,Ddddd}}{reset}
-                                        pick one (default: None)
+                                        pick one {default}(default: {default_value}None{default}){reset}
                   {short_b}+f{reset} {label_b}F{reset}
                   {long_b}++bar{reset} {label_b}BAR{reset}
                   {long_b}-+baz{reset} {label_b}BAZ{reset}

Misc/NEWS.d/next/Library/2025-11-17-21-41-58.gh-issue-141679.fs7zLJ.rst

@@ -0,0 +1 @@
+Add colour to defaults in :mod:`argparse` help. Patch by Hugo van Kemenade.