Replace .update-readme-help.sh with Python script

.github/workflows/readme-updated.yaml

@@ -22,7 +22,7 @@ jobs:
 
       - name: Update README.md helptext
         run: |
-          ./.update-readme-help.sh
+          ./.update-readme-help.py
 
       - name: Ensure no diff
         run: |

.pre-commit-config.yaml

@@ -34,7 +34,7 @@ repos:
     hooks:
       - id: update-readme
         name: Update README with --help output
-        entry: ./.update-readme-help.sh
+        entry: ./.update-readme-help.py
         language: system
   - repo: local
     hooks:

.update-readme-help.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+from pathlib import Path
+import re
+import subprocess
+
+help_content = subprocess.run(
+    ["duct", "--help"], check=True, text=True, encoding="utf-8", stdout=subprocess.PIPE
+).stdout
+
+readme = Path("README.md")
+text = readme.read_text(encoding="utf-8")
+text = re.sub(
+    r"(?<=<!--- BEGIN HELP -->\n).*(?=^<!--- END HELP -->)",
+    help_content,
+    text,
+    flags=re.S | re.M,
+)
+readme.write_text(text, encoding="utf-8")