example.py

from functools import partial
from stringcase import snakecase

def recursively_convert_keys(conversion_fun, data):
    """
    The first major change we're making is pulling the type check out of the loop. This reduces the number of cases
    which we need to handle, and allows us to run the conversion with a dictionary or a list.
    The second change is that we're not mutating the original input. This simplifies things because we don't have
    to delete the old keys, and we don't need to worry about breaking things in code elsewhere.
    """
    if isinstance(data, dict):
        # Convert keys and recursively process values
        return { conversion_fun(k): recursively_convert_keys(conversion_fun, v) for k, v in data.items() }
    elif isinstance(data, list):
        # Recursively process values
        return [recursively_convert_keys(conversion_fun, x) for x in data]
    else:
        # If data isn't a dictionary or a list then it can be left unchanged
        return data


def convert_key(key):
    mapping = {
        "address1": "route",
        "address2": "sublocality",
        "address3": "locality",
        "post_code": "postal_code",
        "country_code": "country",
    }

    snake_key = snakecase(key)
    # Return the value in the mapping dictionary, or the snakecase key if it does not exist.
    return mapping.get(snake_key, snake_key)

convert_keys = partial(recursively_convert_keys, convert_key)

a = {
    "entity_status_code": "80",
    "entity_name": "ASIA PACIFIC DISTRIBUTORS INVESTMENTS NO 2 LIMITED",
    "nzbn": "9429035530732",
    "entity_type_code": "LTD",
    "entity_type_description": "NZ Limited Company",
    "entity_status_description": "Removed",
    "registration_date": "2003-11-20T00:00:00.000+1300",
    "source_register": "COMPANY",
    "source_register_unique_identifier": "1447962",
    "last_updated_date": "2013-10-18T10:54:28.000+1300",
    "australian_business_number": None,
    "email_addresses": None,
    "addresses": {
        "links": None,
        "address_list": [
            {
                "unique_identifier": "7020375",
                "start_date": "2003-11-20T00:00:00.000+1300",
                "end_date": None,
                "care_of": None,
                "address1": "87 Braemar Road",
                "address2": "Castor Bay",
                "address3": "Auckland",
                "address4": None,
                "post_code": None,
                "country_code": "NZ",
                "address_type": "REGISTERED",
                "paf_id": None
            },
        ]
    }
}

print(a)
print(convert_keys(a))