How do I append to a YAML file with python

Question

I have a YAML file called data.yaml:

---
\'001\':
  name: Ben
  email: ben@test.com

I would like to have an updated file that loo

Answer 1

You can, in general, not add to a YAML document in a file by just writing extra information at the end of that file. This migth work for YAML documents that have a mapping or sequence at the top level that is block style, but even then simply appending can only work for certain cases of documents.

It is easy to just load your YAML to Python datastructure, update/extend that structure and then dump it back. That way you don't have to deal with potential duplicate keys, non-bare documents and other issues that will result in invalid YAML when you use simple appending. Assumping your original file is called input.yaml, the following does the trick:

import sys
from pathlib import Path
import ruamel.yaml

file_name = Path('input.yaml')

record_to_add = dict(name='Lisa', email='lisa@test.com', numbers=['000-111-2222', '000-111-2223'])

yaml = ruamel.yaml.YAML()
yaml.explicit_start = True
data = yaml.load(file_name)
data['002'] = record_to_add
yaml.dump(data, sys.stdout)

which gives:

---
'001':
  name: Ben
  email: ben@test.com
'002':
  name: Lisa
  email: lisa@test.com
  numbers:
  - 000-111-2222
  - 000-111-2223