ruamel.yaml removing comments from output YAML

Question

I have the following Python code:

import ruamel.yaml

source = open("source.yaml", "r")
target = open("target.yaml", "r")

sourceValues = ruamel.yaml.load(source, ruamel.yaml.RoundTripLoader, preserve_quotes=True)
targetValues = ruamel.yaml.load(target, ruamel.yaml.RoundTripLoader, preserve_quotes=True)

source.close()
target.close()

# some changes on target properties
targetValues['test']['something'] = sourceValues['test']['something']

with open('target.yaml', 'w') as conf:
  ruamel.yaml.dump(targetValues, conf, ruamel.yaml.RoundTripDumper)

One example of YAML with comments:

test:
  # some comment
  something: "something" # another comment
  else: 123

The above code outputs:

test:
  something: "something-updated"
  else: 123456

Everything works fine, fields are updated as expected, quotes are being kept, code indentation looks OK... But the comments are being lost.

Answer 1

You are using functions from the ruamel.yaml library that were deprecated quite a long time ago.

Your input round-trips without a problem:

import sys
from pathlib import Path
import ruamel.yaml

file_in = Path('target.yaml')
file_in.write_text("""\
test:
  # some comment
  something: "something" # another comment
  else: 123
""")
    
yaml = ruamel.yaml.YAML()
yaml.preserve_quotes = True
data = yaml.load(file_in)
yaml.dump(data, sys.stdout)

as this gives:

test:
  # some comment
  something: "something" # another comment
  else: 123

And this works even if you update data :

data['test']['something'] = 'something-updated'
yaml.dump(data, file_in)
print(file_in.read_text(), end='')

which gives:

test:
  # some comment
  something: "something-updated" # another comment
  else: 123