Keep anchors & aliases on load/dump YAML using ruamel.yaml

Question

How can I avoid ruamel.yaml from merging anchors when using yaml.load? I would like to keep file as is, just modify some keys such as production -> host & production -> port and dump to file

defaults: &defaults
  host: <%= ENV.fetch("VBOX_IP", "127.0.0.1") %>
  adapter: mysql2
  reconnect: true
  encoding: utf8
  username: root

production:
  default:
    <<: *defaults
    host: dbname.domain.com
    port: 3306

Answer 1

If you have that YAML example in file config.yaml then you can do:

import sys
import ruamel.yaml


yaml = ruamel.yaml.YAML()

with open('config.yaml') as ifp:
    data = yaml.load(ifp)
data['defaults']['reconnect'] = False
data['production']['default']['port'] += 1

with open('config.yaml', 'w') as ofp:
    yaml.dump(data, ofp)

to get an updated file:

defaults: &defaults
  host: <%= ENV.fetch("VBOX_IP", "127.0.0.1") %>
  adapter: mysql2
  reconnect: false
  encoding: utf8
  username: root

production:
  default:
    <<: *defaults
    host: dbname.domain.com
    port: 3307

The default YAML() (equivalent to YAML(typ='rt')) will get you the round-trip loader/dumper that preserves both the anchor name and the merge key (<<).

Please note that if you would do:

data['production']['default']['reconnect'] = 'False'

then the reconnect key would be added to the mapping that starts with the merge key.