How do I edit a yaml file using ruamel.yaml package, without changing the indentation of the file?

Question

I am using the code proposed here by Anthon but it doesn't seem to work.

YAML file:

init_config: {}
instances:
    - host: <IP>              # update with IP
      username: <username>    # update with user name
      password: <password>    # update with password

Code:

import ruamel.yaml
yaml = ruamel.yaml.YAML()

file_name = 'input.yaml'
config, ind, bsi = ruamel.yaml.util.load_yaml_guess_indent(open(file_name))

instances = config['instances']
instances[0]['host'] = '1.2.3.4'
instances[0]['username'] = 'Username'
instances[0]['password'] = 'Password'

with open('output.yaml', 'w') as fp:
    yaml.dump(config, fp)

Expected output:

init_config: {}
instances:
    - host: 1.2.3.4           # update with IP
      username: Username      # update with user name
      password: Password      # update with password

Output that I get:

init_config: {}
instances:
- host: 1.2.3.4           # update with IP
  username: Username      # update with user name
  password: Password      # update with password

Am I doing something wrong, or is the example broken? How can I get the expected output?

Answer 1

Somewhere in updating the old round_trip_dump routine in version 4 of that answer to use the YAML() , I forgot to change the arguments indent and block_seq_indent to a call to the .indent() method, as shown in the last code section of that answer.

import sys
import ruamel.yaml


import ruamel.yaml
from ruamel.yaml import YAML
yaml=YAML()

file_name = 'input.yaml'
config, ind, bsi = ruamel.yaml.util.load_yaml_guess_indent(open(file_name))

instances = config['instances']
instances[0]['host'] = '1.2.3.4'
instances[0]['username'] = 'Username'
instances[0]['password'] = 'Password'

yaml.indent(mapping=ind, sequence=ind, offset=bsi)  # <<<< missing
yaml.dump(config, sys.stdout)

which gives:

init_config: {}
instances:
    - host: 1.2.3.4           # update with IP
      username: Username      # update with user name
      password: Password      # update with password

---

I normally make a single .ryd file when I answer on SO. That file has both text and code segments and when processed gets combined with the results of the code output in the form of an answer that I can paste in on SO. That way there is never a discrepancy between code and output.

But that answer is from before I started using that, and I didn't make the .ryd file for the old answer when I updated it. I should have...