Scenario

Three YAML configuration files contain application settings with some overlapping keys. You need to merge them into a single configuration file where values from later files override earlier ones.

Task

Write a Python script at /home/interview/merge_configs.py that merges /home/interview/config1.yaml, /home/interview/config2.yaml, and /home/interview/config3.yaml (in that order) into /home/interview/merged_config.yaml. Later files should override values from earlier files, with deep merging for nested structures. Lists (arrays) should be fully replaced by the later file's value, not appended.

Note: The pyyaml package is already installed.

Example

If config1.yaml has:

database:
  host: localhost
  port: 5432
app:
  debug: true
  plugins:
    - auth
    - logging

And config2.yaml has:

database:
  host: prod-server
app:
  timeout: 30
  plugins:
    - auth
    - metrics

The merged result should be:

database:
  host: prod-server
  port: 5432
app:
  debug: true
  timeout: 30
  plugins:
    - auth
    - metrics

Note that plugins is fully replaced by config2's list, not merged or appended.

Step 1: Examine the configuration files

cat /home/interview/config1.yaml
cat /home/interview/config2.yaml
cat /home/interview/config3.yaml

Review the structure and identify overlapping and unique keys.

Step 2: Create the merge script

nano /home/interview/merge_configs.py

Write a script that performs deep merging of YAML files:

import yaml

def deep_merge(base, override):
    """Recursively merge override dict into base dict"""
    result = base.copy()
    
    for key, value in override.items():
        if key in result and isinstance(result[key], dict) and isinstance(value, dict):
            # Recursively merge nested dictionaries
            result[key] = deep_merge(result[key], value)
        else:
            # Override value
            result[key] = value
    
    return result

# Read all three config files
with open('/home/interview/config1.yaml', 'r') as f:
    config1 = yaml.safe_load(f)

with open('/home/interview/config2.yaml', 'r') as f:
    config2 = yaml.safe_load(f)

with open('/home/interview/config3.yaml', 'r') as f:
    config3 = yaml.safe_load(f)

# Merge configs in order (config1 -> config2 -> config3)
merged = deep_merge(config1, config2)
merged = deep_merge(merged, config3)

# Write merged config to output file
with open('/home/interview/merged_config.yaml', 'w') as f:
    yaml.dump(merged, f)

print("Merged 3 configuration files successfully")

The deep_merge function recursively merges nested dictionaries, preserving keys that aren't overridden while updating those that are.

Step 3: Run the script

python3 /home/interview/merge_configs.py

Step 4: Verify the merged configuration

cat /home/interview/merged_config.yaml

Should show combined configuration with values from config3 taking precedence, config2 overriding config1, and nested structures properly merged.