Takes files in format `yyyy-mm-dd-post-slug-here.markdown` and converts them to `post-slug-here/index.markdown`

convert_jekyll_to_gatsby.py

import frontmatter
from pathlib import Path
import re
import os
import errno

p = Path("./posts")

for path in p.glob("*.markdown"):
    with open(path, mode="r", encoding="UTF-8") as f:
        lines = f.readlines()
        clean_lines = [l.strip() for l in lines if l.strip()]
        post = frontmatter.loads("\n".join(clean_lines))

        # I don't need anything but "title" from the existing frontmatter
        for key in list(post.metadata):
            if key not in ("title"):
                del post.metadata[key]

        # Add date from the old post title to the frontmatter
        match = re.match(r"([\d]{4}-[\d]{2}-[\d]{2})-{1}(.+)", path.stem)
        post["date"] = match.groups()[0]

        slug = match.groups()[1]

        filename = f"converted_posts/{slug}/index.markdown"
        if not os.path.exists(os.path.dirname(filename)):
            try:
                os.makedirs(os.path.dirname(filename))
            except OSError as exc:  # Guard against race condition
                if exc.errno != errno.EEXIST:
                    raise

        with open(filename, mode="w") as of:
            of.write(frontmatter.dumps(post))