#563 TypeError: 'CommentToken' object is not iterable

[Jimmy]

Here is a minimal working example that reproduces the issue:

"""
ruamel.yaml bug: yaml_value_comment_extend() crashes when adding EOL comment
to a key that already has a comment (loaded from YAML)

Bug location: ruamel/yaml/comments.py, method yaml_value_comment_extend()

When loading YAML with existing EOL comments, then calling yaml_add_eol_comment()
on the same key, the else branch in yaml_value_comment_extend() executes:
    r[3].extend(comment[0])

But comment[0] is a CommentToken, not a list, causing:
    TypeError: 'CommentToken' object is not iterable
"""

from ruamel.yaml import YAML, version_info
from io import StringIO

print(f"ruamel.yaml version: {'.'.join(map(str, version_info))}")

yaml = YAML()

def test_add_eol_comment_to_existing_comment():
    """
    Minimal reproduction:

    1. Load YAML that has an existing EOL comment on a key with list value
    2. Try to add/update the EOL comment on that same key
    3. Crash with TypeError: 'CommentToken' object is not iterable
    """

    # YAML with existing EOL comment on 'items' key
    yaml_content = """\
config:
    items: # existing comment

    -   name: item1
        value: 100
"""

    data = yaml.load(yaml_content)

    # Debug: show the internal comment structure after loading
    print("After loading, ca.items['items']:")
    print(f"  {data['config'].ca.items['items']}")
    # Output: [None, None, CommentToken('# existing comment\n', ...), []]
    # Note: r[3] is an empty list []

    # This crashes when trying to add EOL comment to a key that already has one
    # The bug is in yaml_value_comment_extend() else branch:
    #   - r = [None, None, CommentToken(...), []]  (from loaded YAML)
    #   - comment = [CommentToken(...), None]      (new comment)
    #   - r[3].extend(comment[0])  <-- BUG: comment[0] is CommentToken, not list!
    data['config'].yaml_add_eol_comment('new comment', key='items')

    # Expected: comment should be updated to 'new comment'
    stream = StringIO()
    yaml.dump(data, stream)
    print(stream.getvalue())


def workaround():
    """
    Workaround: delete existing comment before adding new one
    """
    yaml_content = """\
config:
    items: # existing comment

    -   name: item1
        value: 100
"""

    data = yaml.load(yaml_content)

    # Workaround: clear existing comment first
    if 'items' in data['config'].ca.items:
        del data['config'].ca.items['items']

    # Now this works
    data['config'].yaml_add_eol_comment('new comment', key='items')

    stream = StringIO()
    yaml.dump(data, stream)
    print("Workaround output:")
    print(stream.getvalue())


if __name__ == '__main__':
    print("=" * 60)
    print("Bug reproduction:")
    print("=" * 60)
    try:
        test_add_eol_comment_to_existing_comment()
    except TypeError as e:
        print(f"\nCrashed with: {type(e).__name__}: {e}")

    print("\n" + "=" * 60)
    print("Workaround:")
    print("=" * 60)
    workaround()

output:

(chatui) PS E:\program\ChatUI\tmp_test> uv run .\ruamel_yaml_bug_report.py
ruamel.yaml version: 0.19.1
============================================================
Bug reproduction:
============================================================
After loading, ca.items['items']:
  [None, None, CommentToken('# existing comment\n', line: 1, col: 11), []]

Crashed with: TypeError: 'CommentToken' object is not iterable

============================================================
Workaround:
============================================================
Workaround output:
config:
  items:  # new comment

  - name: item1
    value: 100