Simple string-valued parser for YAML supporting

yaml_loads.py

# supports only strings, dicts and lists
# does not support multiline strings as the first list-item key `- run: |`
# does not preserve whitespaces in " |" literal string blocks as described in : https://docs.ansible.com/ansible/latest/reference_appendices/YAMLSyntax.html

def yaml_loads(content, convert_bool = True, convert_int = True, convert_dict = True):
    def procval(val):
        read_until = lambda tail, chars: ([(tail[:i], tail[i+1:]) for i, c in enumerate(tail) if c in chars] or [(tail, '')])[0]

        val = val.strip()
        is_quoted_string = len(val) >= 2 and ((val[0] == val[-1] == '"') or (val[0] == val[-1] == "'"))
        if is_quoted_string:
            return val[1:-1]
        else:
            val = val.split('#', maxsplit = 1)[0].strip()
            is_int = val.isdigit()
            is_bool = val in ['true', 'false']
            is_dict = len(val) >= 2 and (val[0] == '{' and val[-1] == '}')
            if is_int and convert_int:
                return int(val) if convert_int else val
            elif is_bool and convert_bool:
                return dict(true = True, false = False)[val] if convert_int else val
            elif is_dict and convert_dict:
                res = {}
                tail = val
                head, tail = read_until(tail, '{')
                while tail:
                    key, tail = read_until(tail, ':')
                    val, tail = read_until(tail, ',}')
                    res[key.strip()] = procval(val.strip())
                return res
        return val

    lines = content.strip().splitlines()

    res = {}
    keyprev = ''
    indentprev = 0
    dictprev = {}
    is_multiline = False
    stack = {0: ({None: res}, None)}
    begin_multiline_indent = 0

    for line in lines:
        line_lstrip = line.lstrip()
        line_strip = line.strip()
        indent = len(line) - len(line_lstrip)
        splitted_colon = line.split(':', maxsplit = 1)
        key, val = (splitted_colon[0].strip(), splitted_colon[1].strip()) if len(splitted_colon) > 1 else ('', line_strip)
        list_val = line_strip.split('- ', maxsplit = 1)[-1]
        is_list_item = line_lstrip.startswith('- ')
        is_comment = not line_strip or line_lstrip.startswith('#')
        is_dedent = indent < indentprev
        begin_multiline = val in ['>', '|', '|>']
        is_record = len(list_val) >= 2 and list_val[0] == '{' and list_val[-1] == '}'

        if is_multiline and begin_multiline_indent and indent < begin_multiline_indent:
            is_multiline = False
            begin_multiline_indent = 0

        if not is_multiline:
            if indent not in stack:
                stack[indent] = (stack[indentprev][0][stack[indentprev][1]], keyprev) if keyprev is not None else ({None: dictprev}, None)
            curdict, curkey = stack[indent]

        if is_comment:
            continue

        elif is_list_item:
            curdict[curkey] = curdict[curkey] or []
            if not key or is_record:
                curdict[curkey].append(procval(list_val))
            else:
                dictprev = {key.removeprefix('- ') : procval(val)}
                curdict[curkey].append(dictprev)
                key = None

        elif begin_multiline:
            curdict[curkey][key] = ''
            curdict, curkey = curdict[curkey], key
            is_multiline = True

        elif is_multiline:
            curdict[curkey] += ('\n' + val) if curdict[curkey] else val
            begin_multiline_indent = min(indent, begin_multiline_indent) if begin_multiline_indent else indent

        elif key and not val:
            curdict[curkey][key] = dictprev = {}

        else:
            curdict[curkey][key] = procval(val)

        if is_dedent:
            stack = {i : v for i, v in stack.items() if i <= indent}

        indentprev = indent
        keyprev = key

    return res

if __name__ == '__main__':
    # https://github.com/jekyll/minima/blob/demo-site/_config.yml
    yaml_str = """
title: Your awesome title
author:
  name: GitHub User
  email: your-email@domain.com
description: >
  Write an awesome description for your new site here. You can edit this
  line in _config.yml. It will appear in your document head meta (for
  Google search results) and in your feed.xml site description.

minima:
  date_format: "%b %-d, %Y"
  social_links:
    - { platform: devto,          user_url: "https://dev.to/jekyll" }
    - { platform: dribbble,       user_url: "https://dribbble.com/jekyll" }
    - { platform: facebook,       user_url: "https://www.facebook.com/jekyll" }
    - { platform: flickr,         user_url: "https://www.flickr.com/photos/jekyll" }
    - { platform: github,         user_url: "https://github.com/jekyll/minima" }
    - { platform: google_scholar, user_url: "https://scholar.google.com/citations?user=qc6CJjYAAAAJ" }
    - { platform: instagram,      user_url: "https://www.instagram.com/jekyll" }
    - { platform: keybase,        user_url: "https://keybase.io/jekyll" }
    - { platform: linkedin,       user_url: "https://www.linkedin.com/in/jekyll" }
    - { platform: microdotblog,   user_url: "https://micro.blog/jekyll" }
    - { platform: pinterest,      user_url: "https://www.pinterest.com/jekyll" }
    - { platform: stackoverflow,  user_url: "https://stackoverflow.com/users/1234567/jekyll" }
    - { platform: telegram,       user_url: "https://t.me/jekyll" }
    - { platform: twitter,        user_url: "https://twitter.com/jekyllrb" }
    - { platform: youtube,        user_url: "https://www.youtube.com/jekyll" }
    - { platform: rss,            user_url: "https://jekyll.github.io/minima/feed.xml" }

show_excerpts: false # set to true to show excerpts on the homepage

# Build settings
baseurl: /minima
remote_theme: jekyll/minima
plugins:
  - jekyll-feed
  - jekyll-remote-theme
  - jekyll-seo-tag
"""
    yaml_dict = yaml_loads(yaml_str)
    import json
    print(json.dumps(yaml_dict, indent = 2))