Dev Notes

Software Development Resources by David Egan.

Access YAML Values from Frontmatter Using Python

David Egan

Access nested (or not) YAML values using Python. Used within a Makefile to set variables from either Markdown frontmatter or YAML config files.

Uses the Python 3 yaml module’s load_all method - this is necessary if accessing YAML within a frontmatter block (e.g. at the start of a markdown file), since the normal frontmatter delimiters cause the Python module to treat the YAML block as the first in a series of YAML documents.

The function receives a list of YAML keys key_list ordered from highest to lowest level, allowing access to nested elements.

For example:

name: Rocky
  line 1: 22 Acacia Ave
  line 2: London

To access the value “London”, run ./ address "line 2".

To access the value “Rocky”, run ./ name.

#!/usr/bin/env python3

import sys, os, yaml

def main(filename, key_list):
    project_dir = os.path.realpath('.')
    filepath = os.path.join(project_dir, filename)
    with open(filepath, "r") as f:
        # Make a dict from the first YAML block
        data = next(yaml.load_all(f, Loader=yaml.FullLoader))
        # If there are multiple keys, we need to step down a hierarchy of keys
        # to reach the correct value. At each iteration, set data to be a new
        # simpler dict (or the final value if we're at the last key) by accessing
        # the value by it's key.  
        for key in key_list: data = data[key]

if __name__ == '__main__':
    main(sys.argv[1], sys.argv[2:])

comments powered by Disqus