[Python] Using Yaml Anchors across different files using python / ruamel.yaml

I have created 2 YAML files that look like the following:

file1.yaml:

variables:
host1: &host1 'https://example.com'


file2.yaml:

app:
host: *host1


As you can see I want to use the YAML anchor &host1 in a different YAML file. Now I know that YAML does not support this but it is possible using a Python script and ruamel.yaml.

import ruamel.yaml

def load_and_merge_yaml(base_file, target_file):
yaml = ruamel.yaml.YAML()

# Load the base YAML file (contains anchors)
with open(base_file, 'r') as base_file_obj:
base_data = yaml.load(base_file_obj)

# Load the target YAML file (we want to reuse anchors here)
with open(target_file, 'r') as target_file_obj:
target_data = yaml.load(target_file_obj)

# Manually merge the base data into the target data
# We will handle this by iterating through the base data and adding/replacing it in the target.
# If a key exists in the base data, we will add it to the target if it's missing
def merge_dicts(base, target):
for key, value in base.items():
if isinstance(value, dict):
# If the value is a dictionary, we recursively merge
if key not in target:
target[key] = {} # Create the key if it's missing
merge_dicts(value, target[key]) # Recursively merge nested dictionaries
else:
# If the value is not a dictionary, just assign it to the target
if key not in target:
target[key] = value # Add if missing

# Perform the merge
merge_dicts(base_data, target_data)

# Save the merged result to a new file
with open('merged_output.yaml', 'w') as output_file:
yaml.dump(target_data, output_file)

return target_data

# Example usage
base_file = 'file1.yaml' # The file containing the anchors
target_file = 'file2.yaml' # The file where we want to apply anchors
merged_data = load_and_merge_yaml(base_file, target_file)

# Print the merged data for inspection
print(ruamel.yaml.dump(merged_data, default_flow_style=False))


And people tell me this should work but unfortunately I keep getting this error:

ruamel.yaml.composer.ComposerError: found undefined alias 'host1'
in "file2.yaml", line 2, column 9


Does anyone know what I'm doing wrong? Below is the output I would like.

app:
host: 'https://example.com'

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