Is it possible to use PyYAML to read a text file written with a “YAML front matter” block inside?

Question

I\'m sorry, I know very little of both YAML and PyYAML but I felt in love with the idea of supporting a configuration file written in the same style used by \"Jekyll\" (http

Answer 1

You can accomplish this without any custom parsing by calling yaml.load_all() instead. This will return a generator of which the first item is the expected front matter as a dict, and the second is the rest of the document as a string:

import yaml

with open('some-file-with-front-matter.md') as f:
    front_matter, content = list(yaml.load_all(f, Loader=yaml.FullLoader))[:2]

If you just want the front matter it's even simpler:

import yaml

with open('some-file-with-front-matter.md') as f:
    front_matter = next(yaml.load_all(f, Loader=yaml.FullLoader))

This works because yaml.load_all() is for loading several YAML documents within the same document, delimited by ---. Also, make sure you take the usual precautions when loading YAML from an unknown source.

EDIT: Updated the code to include a Loader argument which is required now, and updated the documentation link. Also verified the code works even with --- in the content, per comment below.

Answer 2

The Python yaml library does not support reading yaml that is embedded in a document. Here is a utility function that extracts the yaml text, so you can parse it before reading the remainder of the file:

#!/usr/bin/python2.7

import yaml
import sys

def get_yaml(f):
  pointer = f.tell()
  if f.readline() != '---\n':
    f.seek(pointer)
    return ''
  readline = iter(f.readline, '')
  readline = iter(readline.next, '---\n')
  return ''.join(readline)


for filename in sys.argv[1:]:
  with open(filename) as f:
    config = yaml.load(get_yaml(f))
    text = f.read()
    print "TEXT from", filename
    print text
    print "CONFIG from", filename
    print config