How to Validate Data Fields and Types in Python

import json
from typing import Any, Dict, List


def validate_data(data: Dict[str, Any], required_fields: List[str]) -> List[str]:
    """Check required fields exist and are non-empty. Return list of errors."""
    errors = []
    for field in required_fields:
        value = data.get(field)
        if value is None or value == "":
            errors.append(f"Missing or empty required field: {field}")
    return errors


def validate_types(data: Dict[str, Any], type_map: Dict[str, type]) -> List[str]:
    """Verify fields match expected types. Return list of errors."""
    errors = []
    for field, expected_type in type_map.items():
        if field in data and not isinstance(data[field], expected_type):
            errors.append(
                f"Field '{field}' must be {expected_type.__name__}, got {type(data[field]).__name__}"
            )
    return errors


if __name__ == "__main__":
    sample_payload = {
        "user_id": 123,
        "email": "joe@example.com",
        "score": "high",
        "tags": ["python", "cloud"],
    }

    required = ["user_id", "email", "password"]
    types = {"user_id": int, "email": str, "tags": list}

    all_errors = validate_data(sample_payload, required) + validate_types(sample_payload, types)

    print(json.dumps(sample_payload, indent=2))
    print(f"Validation errors: {len(all_errors)}")
    for error in all_errors:
        print(f"- {error}")