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.- bphase2:- 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.)

The problem here is that the empty line is considered to be sort of a comment and that comments in ruamel.yaml are preserved by associating them with elements in a sequence or with keys in a mapping. That value is stored in a complex attribute named ca, on the list like object doc['phase1'], associated with the second element.

You can of course argue that it should be associated on the top level mapping/dict either associated with key phase1 (as some final empty-line-comment) or with phase2 as some introductory empty-line-comment. Either of the above three is valid and there is currently no control in the library over the strategy, where the empty line (or a comment goes).

If you put in a "real" comment (one starting with #) it will be associated with phase1 as an end comment, for those the strategy is different.

This obviously needs an overhaul, as the original goal of ruamel.yaml was: - load some configuration from YAML - change some value - save the configuration to YAML in which case these kind of append/insert problems don't appear.

So there is no real solution until the library is extended with some control over where to attach (trailing) comments and/or empty lines.

Until such control gets implemented, probably the best thing you can do is the following:

import sys
import ruamel.yamlyaml_str = """\
phase1:- a# a comment.- bphase2:- d
"""def append_move_comment(l, e):i = len(l) - 1l.append(e)x = l.ca.items[i][0]  # the end commentif x is None:returnl.ca.items[i][0] = Nonel.ca.items[i+1] = [x, None, None, None]data = ruamel.yaml.round_trip_load(yaml_str)
append_move_comment(data['phase1'], 'c')
ruamel.yaml.round_trip_dump(data, sys.stdout, indent=4, block_seq_indent=2)

I changed the indent value to 4, which is what your input has (and get because you specify it as to small for the block_seq_indent).