Generate CHANGELOG from Conventional Commits in Python

import subprocess
import re
import sys
from collections import OrderedDict

CONVENTIONAL_COMMIT = re.compile(
    r"^(?P<type>feat|fix|chore|docs|refactor|perf|test|build|ci|style)(?:\((?P<scope>[^)]+)\))?: (?P<description>.+)"
)


def get_git_log():
    return subprocess.run(
        ["git", "log", "--format=%s"],
        capture_output=True,
        text=True,
        check=True,
    ).stdout.splitlines()


def parse_conventional_commits(commits):
    grouped = OrderedDict()
    for commit in commits:
        match = CONVENTIONAL_COMMIT.match(commit)
        if match:
            commit_type = match.group("type")
            scope = match.group("scope")
            description = match.group("description")
            if commit_type in ("feat", "fix"):
                prefix = f"**{scope}:** " if scope else ""
                grouped.setdefault(commit_type, []).append(f"{prefix}{description}")
    return grouped


def generate_changelog():
    commits = get_git_log()
    parsed = parse_conventional_commits(commits)

    changelog_lines = ["# Changelog", ""]
    if "feat" in parsed:
        changelog_lines.append("## Features")
        for item in parsed["feat"]:
            changelog_lines.append(f"- {item}")
        changelog_lines.append("")
    if "fix" in parsed:
        changelog_lines.append("## Bug Fixes")
        for item in parsed["fix"]:
            changelog_lines.append(f"- {item}")
        changelog_lines.append("")
    return "\n".join(changelog_lines).strip()


if __name__ == "__main__":
    try:
        print(generate_changelog())
    except subprocess.CalledProcessError:
        print("Error: not a git repository", file=sys.stderr)
        sys.exit(1)