[Python] processing a python yaml file tag with attribue

!Employee old:
id: some_id
name: John
cfg:
param: "abc"


I need to load update, and save a yaml file, which contains a structure, similar to the above.

I tried using add_constructor and add_representer. WHich worked when the Tag is placed separately.

!Employee
old:
id: some_id
name: John
cfg:
param: "abc"


I would like nevertheless to avoid the preporcessing of the original file. Also I dont have ruamel (suggested on other posts).

In the example below yaml does does not seen to scan the entire structure, i.e. does not include the mapping part under the tag.

#====================================================================

import yaml


# Custom class to handle !Employee old: name: Peter
class Employee:
def __init__(self, status, data=None):
self.status = status # e.g., "old"
self.data = data or {} # e.g., {'name': 'Peter'}

def __repr__(self):
return f"!Employee {self.status}: {self.data}"


# Custom constructor for the !Employee tag
def employee_constructor(loader, node):
# Check if the node is a MappingNode
print(f"EMPL_CONST node: {node}")
if isinstance(node, yaml.MappingNode):
# Expecting only one key-value pair (e.g., "old": {"name": "Peter"})
print(f"EMPL_CONST node: {node.value[0]}")
first_key_node, value_node = node.value[0]

# The key is the scalar "old"
status = loader.construct_scalar(first_key_node)

# The value is the mapping part {"name": "Peter"}
data = loader.construct_mapping(value_node)

# Return an Employee object with the status and data
return Employee(status, data)

raise yaml.constructor.ConstructorError(None, None, f"Unexpected node type: {type(node)}", node.start_mark)


# Custom representer for the !Employee tag
def employee_representer(dumper, data):
# Create a tag with the status (e.g., !Employee old)

tag = f"!Employee"
return dumper.represent_mapping(tag, {data.status: data.data})

# Register the custom constructor and representer
yaml.add_constructor('!Employee', employee_constructor)
yaml.add_representer(Employee, employee_representer)

def load_yaml(file_path):
with open(file_path, 'r') as file:
data = yaml.load(file, Loader=yaml.FullLoader)
# print(data)
return data
def save_yaml(file_path, data):
with open(file_path, 'w') as file:
yaml.dump(data, file, default_flow_style=False)

# Testing the code
if __name__ == "__main__":
yaml_string = """
!Employee old:
name: Some_Name
id: some_id

cfg:
param : 'abc'
"""

# Load the YAML data`your text`
data = yaml.load(yaml_string, Loader=yaml.FullLoader)
# data = load_yaml("input3.yaml")
print("Loaded YAML data:")
print(data)

# Modify the data (optional)
data['cfg']['param'] = 'xyz'

# Dump the data back to YAML format
output = yaml.dump(data, default_flow_style=False)
print("\nModified YAML output:")
print(output)
save_yaml("output3.yaml", data)

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