[Python] Modifying YAML using ruamel.yaml adds extra new lines

I need to add an extra value to an existing key in a YAML file. Following is the code I'm using.

with open(yaml_in_path, 'r') as f:
doc, ind, bsi = load_yaml_guess_indent(f, preserve_quotes=True)
doc['phase1'] += ['c']
with open(yaml_out_path, 'w') as f:
ruamel.yaml.round_trip_dump(doc, f,
indent=2, block_seq_indent=bsi)


This is the input and output.

Input

phase1:
- a
# a comment.
- b

phase2:
- d


Output

phase1:
- a
# a comment.
- b

- c
phase2:
- d


How can I get rid of the new line between b and c? (This problem is not there when phase1 is the only key in the file or when there are no blank lines between phase1 and phase2.)

Continue reading...