How to Generate Release Notes from Git Commit Messages in Python

import subprocess
import re
from datetime import datetime

def get_git_log(since_tag="HEAD~10", format_str="%s"):
    """Retrieve commit messages from git log."""
    try:
        result = subprocess.run(
            ["git", "log", f"--since={since_tag}", f"--format={format_str}"],
            capture_output=True,
            text=True,
            check=True
        )
        return result.stdout.strip().split("\n")
    except subprocess.CalledProcessError:
        return []

def categorize_commit(msg):
    """Categorize commit message by conventional commit prefix."""
    patterns = {
        "Features": r"^feat(?:\(.*?\))?:",
        "Bug Fixes": r"^fix(?:\(.*?\))?:",
        "Refactoring": r"^refactor(?:\(.*?\))?:",
        "Documentation": r"^docs(?:\(.*?\))?:",
        "Chores": r"^chore(?:\(.*?\))?:"
    }
    for category, pattern in patterns.items():
        if re.match(pattern, msg, re.IGNORECASE):
            return category
    return "Other Changes"

def generate_release_notes():
    """Main function to produce release notes from git history."""
    messages = [m for m in get_git_log() if m.strip()]
    if not messages:
        print("No commit messages found.")
        return

    categories = {}
    for msg in messages:
        cat = categorize_commit(msg)
        # Remove the prefix for cleaner output
        clean_msg = re.sub(r"^(feat|fix|refactor|docs|chore)(\(.*?\))?:\s*", "", msg, flags=re.IGNORECASE).strip()
        categories.setdefault(cat, []).append(clean_msg)

    print(f"## Release Notes ({datetime.now().strftime('%Y-%m-%d')})\n")
    for category, items in categories.items():
        if items:
            print(f"### {category}")
            for item in items:
                print(f"- {item}")
            print()

if __name__ == "__main__":
    generate_release_notes()