Colorize help output

git_delete_merged_branches/__main__.py

@@ -2,6 +2,7 @@
 # Licensed under GPL v3 or later
 
 import argparse
+import os
 import re
 import sys
 import traceback
@@ -13,6 +14,9 @@
 from textwrap import dedent
 from typing import List, Set
 
+import colorama
+
+from ._argparse_color import add_color_to_formatter_class
 from ._confirm import Confirmation
 from ._git import Git
 from ._metadata import APP, DESCRIPTION, VERSION
@@ -246,9 +250,15 @@ def _parse_command_line():
         Please report bugs at https://github.com/hartwork/{APP}.  Thank you!
     """)
 
+    colorize = 'NO_COLOR' not in os.environ
+    formatter_class = RawDescriptionHelpFormatter
+    if colorize:
+        colorama.init()
+        formatter_class = add_color_to_formatter_class(formatter_class)
+
     parser = argparse.ArgumentParser(prog='git-delete-merged-branches', add_help=False,
                                      description=DESCRIPTION, epilog=_EPILOG,
-                                     formatter_class=RawDescriptionHelpFormatter)
+                                     formatter_class=formatter_class)
 
     modes = parser.add_argument_group('modes').add_mutually_exclusive_group()
     modes.add_argument('--configure', dest='force_reconfiguration', action='store_true',

git_delete_merged_branches/_argparse_color.py

@@ -0,0 +1,39 @@
+# Copyright (C) 2020 Sebastian Pipping <sebastian@pipping.org>
+# Licensed under GPL v3 or later
+
+import re
+
+import colorama
+
+_SECTION_COLOR = colorama.Fore.WHITE + colorama.Style.BRIGHT
+_ARGUMENT_COLOR = colorama.Fore.GREEN + colorama.Style.BRIGHT
+_PARAMETER_COLOR = colorama.Fore.GREEN
+_PROG_COLOR = colorama.Fore.CYAN + colorama.Style.BRIGHT
+_URL_COLOR = colorama.Fore.MAGENTA + colorama.Style.BRIGHT
+_RESET_COLOR = colorama.Style.RESET_ALL
+
+_SUBSTITUTIONS = (
+    ('^(.+):$', f'{_SECTION_COLOR}\\1{_RESET_COLOR}:'),
+    ('(?<!\\w)(--?[a-z-]+) ([A-Z_]+)',
+     f'{_ARGUMENT_COLOR}\\1{_RESET_COLOR} {_PARAMETER_COLOR}\\2{_RESET_COLOR}'),
+    ('(?<!\\w)(--?[a-z-]+)', f'{_ARGUMENT_COLOR}\\1{_RESET_COLOR}'),
+    ('^(usage): ([^ ]+)\\b',
+     f'{_SECTION_COLOR}\\1{_RESET_COLOR}: {_PROG_COLOR}\\2{_RESET_COLOR}'),
+    ('(https://[^ ]+[^ .])', f'{_URL_COLOR}\\1{_RESET_COLOR}'),
+)
+
+
+def add_color_to_formatter_class(formatter_class):
+    class_name = formatter_class.__name__.replace('Formatter', 'ColorFormatter')
+
+    class Class(formatter_class):
+        def format_help(self):
+            text = super().format_help()
+            for pattern, replacement in _SUBSTITUTIONS:
+                matcher = re.compile(pattern, flags=re.MULTILINE)
+                text = matcher.sub(replacement, text)
+            return text
+
+    Class.__name__ = class_name
+
+    return Class