How to Parse and Extract Nested Data in Python

import json
from pathlib import Path
from typing import Any, Dict, List, Union

def load_data(filepath: Union[str, Path]) -> Union[Dict[str, Any], List[Any]]:
    """Load JSON data from a file with modern Path handling."""
    path = Path(filepath)
    if not path.exists():
        raise FileNotFoundError(f"File not found: {path}")
    with path.open("r", encoding="utf-8") as f:
        return json.load(f)

def extract_values(data: Union[Dict[str, Any], List[Any]], key: str) -> List[Any]:
    """Recursively extract all values for a given key from nested structures."""
    results = []
    if isinstance(data, dict):
        for k, v in data.items():
            if k == key:
                results.append(v)
            results.extend(extract_values(v, key))
    elif isinstance(data, list):
        for item in data:
            results.extend(extract_values(item, key))
    return results

if __name__ == "__main__":
    sample_data = {
        "users": [
            {"name": "Alice", "age": 30},
            {"name": "Bob", "age": 25}
        ],
        "metadata": {"source": "demo"}
    }
    print("Extracted names:", extract_values(sample_data, "name"))
    print("Extracted ages:", extract_values(sample_data, "age"))

    # Demonstrate file loading with a small temp file
    temp_file = Path("sample.json")
    temp_file.write_text(json.dumps(sample_data), encoding="utf-8")
    loaded = load_data(temp_file)
    print("Loaded from file:", loaded["metadata"]["source"])
    temp_file.unlink()