I’m encountering an issue with preserving YAML anchors for numeric value, particularly with the number 0 all the other numeric value works fine, when using ruamel.yaml. Here’s what’s happening:

Context: I’m using ruamel.yaml to parse and manipulate YAML files in Python. I need to keep anchors for numeric values intact, but here’s the problem:

from ruamel.yaml import YAML, ScalarInt, PlainScalarString

# Custom loader to attempt to preserve anchors for numeric values
class CustomLoader(YAML):
    def __init__(self):
        super().__init__(typ='rt')
        self.preserve_quotes = True
        self.explicit_start = True
        self.default_flow_style = False

    def construct_yaml_int(self, node):
        value = super().construct_yaml_int(node)
        if node.anchor:
            # Preserve the anchor for numeric values
            if value == 0:
                return PlainScalarString("0", anchor=node.anchor.value)
            else:
                return ScalarInt(value, anchor=node.anchor.value)
        return value

yaml = CustomLoader()

# Load the YAML file
with open('current.yaml', 'r') as current_file:
    current_data = yaml.load(current_file)
    print("Debug: current_data after load:", current_data)
    for key, value in current_data.items():
        print(f"Debug: Key '{key}', value type: {type(value)}, has anchor: {hasattr(value, 'anchor')}, anchor value: {getattr(value, 'anchor', None)}")

current.yaml:

person: &person_age 0
person: &person_age 1 # this works

Expected Behavior: The anchor &person_age should be preserved for the person key with the value 0.

Actual Behavior: The anchor is not preserved; hasattr(value, 'anchor') returns False, and the value type is <class 'int'> rather than ScalarInt or PlainScalarString with an anchor.

What I’ve tried: I’ve tried to override construct_yaml_int in a custom loader to manually preserve anchors for integers, but it doesn’t seem to work. I’ve ensured that ruamel.yaml is configured with typ='rt' for round-trip preservation. I’ve experimented with quoting the 0 in the YAML file (person: &person_age "0"), which does preserve the anchor, but this isn’t a feasible solution for my use case where users might not quote their numeric values.

Question: How can I ensure that anchors are preserved for numeric value 0, when using ruamel.yaml? Is there a way to force ruamel.yaml to handle anchors for numbers without needing them to be quoted in the source YAML?

Any insights or alternative approaches would be greatly appreciated.

Version- [Python:3.12.5, ruamel.yaml:0.18.6]