How to Implement Slowly Changing Dimension Type 2 History in Python

from datetime import datetime, timedelta

def apply_scd_type2(records, current_date):
    """Returns active records after inserting new records with type-2 history."""
    history = []
    active = {}

    for record in records:
        key = record["customer_id"]
        if key in active:
            active[key]["end_date"] = current_date - timedelta(days=1)
            history.append(active[key])
        record["start_date"] = current_date
        record["end_date"] = None
        active[key] = record
    return history + list(active.values())


if __name__ == "__main__":
    base_date = datetime(2024, 1, 1)
    records = [
        {"customer_id": 1, "address": "123 A St", "start_date": None, "end_date": None},
        {"customer_id": 2, "address": "456 B Ave", "start_date": None, "end_date": None},
        {"customer_id": 1, "address": "789 C Blvd", "start_date": None, "end_date": None},
    ]

    for i, relation in enumerate(apply_scd_type2(records, base_date + timedelta(days=i)), 1):
        print(f"customer {relation['customer_id']}: {relation['address']} | start={relation['start_date'].date()} | end={relation['end_date'].date() if relation['end_date'] else 'current'}")