Any idea for a more elegant / simplest conditionnal return?

Question

Here is the Python code:

def _get_handler_by_topic_arn(topic_arn: str, event_name: str, event_message: dict):
    if topic_arn == CONFIG.get("MT_MAIN_SNS_TOPIC_ARN"):
        return MT_MAIN_TOPIC_HANDLERS.get(event_name)
    if topic_arn == CONFIG.get("FOX_REQUEST_SNS_TOPIC_ARN"):
        return FOX_REQUEST_TOPIC_HANDLERS.get(event_name)
    if topic_arn == CONFIG.get("FOX_ORDER_RESULTS_SNS_TOPIC_ARN"):
        if event_message.get("status") and event_message.get("status") != "CANCELLED":
            return None
        return FOX_ORDER_RESULTS_TOPIC_HANDLERS.get(event_name)
    return None

It works but I’m searching for a more efficient / elegant / simplest way to do the same. If you have any idea, I’ll take it :).

Asked By: Asthonishia

||

Source

Answer 1

I would refactor your code like this, so it’s less crowded and also there is only one return point (so the control flow is easier to examine).

def _get_handler_by_topic_arn(topic_arn: str, event_name: str, event_message: dict):
    ret_value = None
    
    # Give a better name to conds
    cond1 = topic_arn == CONFIG.get("MT_MAIN_SNS_TOPIC_ARN")
    cond2 = topic_arn == CONFIG.get("FOX_REQUEST_SNS_TOPIC_ARN")
    cond3 = topic_arn == CONFIG.get("FOX_ORDER_RESULTS_SNS_TOPIC_ARN")
    cond4 = event_message.get("status") and event_message.get("status") != "CANCELLED"
    
    if cond1:
        ret_value = MT_MAIN_TOPIC_HANDLERS.get(event_name)
    elif cond2:
        ret_value = FOX_REQUEST_TOPIC_HANDLERS.get(event_name)
    elif cond3:
        if cond4:
            ret_value = None
        else:
            ret_value = FOX_ORDER_RESULTS_TOPIC_HANDLERS.get(event_name)
    
    return ret_value

Answered By: Fra93

Answer 2

you could also do something like

topics = {
    "MT_MAIN_SNS_TOPIC_ARN" : MT_MAIN_TOPIC_HANDLERS,
    "FOX_REQUEST_SNS_TOPIC_ARN" : FOX_REQUEST_TOPIC_HANDLERS,
    "FOX_ORDER_RESULTS_SNS_TOPIC_ARN" : FOX_ORDER_RESULTS_TOPIC_HANDLERS
}

def _get_handler_by_topic_arn(topic_arn: str, event_name: str, event_message: dict):
    for k,v in topics.items():
        if topic_arn == CONFIG.get(k):
            return v.get(event_name)

Answered By: dotheM

Answer 3

You can use a dictionary to avoid the ifs:

def _get_handler_by_topic_arn(topic_arn: str, event_name: str, event_message: dict):
    not_canceled = event_message.get("status") and event_message.get("status") != "CANCELLED"

    handlers = {
        CONFIG.get("MT_MAIN_SNS_TOPIC_ARN"): MT_MAIN_TOPIC_HANDLERS.get(event_name),
        CONFIG.get("FOX_REQUEST_SNS_TOPIC_ARN"): FOX_REQUEST_TOPIC_HANDLERS.get(event_name),
        CONFIG.get("FOX_ORDER_RESULTS_SNS_TOPIC_ARN"): None if not_canceled else FOX_ORDER_RESULTS_TOPIC_HANDLERS.get(event_name)
    }

    return handlers.get(topic_arn)

Since the function can also return None if the status is not CANCELLED, the dictionary takes that into account when setting the value for the key CONFIG.get("FOX_ORDER_RESULTS_SNS_TOPIC_ARN").

Also, you can customize what will be returned if the topic_arn doesn’t exist. To do that, just pass the default return to handlers.get(topic_arn), like so:

handlers.get(topic_arn, "NOT FOUND")

Answered By: Brhaka

Answer 4

Here’s an approach with a handler map and a validator map to decouple the validation logic from the handling logic:

HANDLER_MAP = {
    CONFIG.get("MT_MAIN_SNS_TOPIC_ARN"): MT_MAIN_TOPIC_HANDLERS,
    CONFIG.get("FOX_REQUEST_SNS_TOPIC_ARN"): FOX_REQUEST_TOPIC_HANDLERS,
    CONFIG.get("FOX_ORDER_RESULTS_SNS_TOPIC_ARN"): FOX_ORDER_RESULTS_TOPIC_HANDLERS
}

VALIDATOR_MAP = {
    CONFIG.get("FOX_ORDER_RESULTS_SNS_TOPIC_ARN"): lambda message: message.get("status") != "CANCELLED"
}

def get_handler_and_validator(topic_arn: str) -> tuple[dict, Callable]:
    handler = HANDLER_MAP.get(topic_arn, {})
    validator = VALIDATOR_MAP.get(topic_arn, lambda _: True)
    return handler, validator

def _get_handler_by_topic_arn(topic_arn: str, event_name: str, event_message: dict):
    topic_handler, validator = get_handler_and_validator(topic_arn)
    if validator(event_message):
        return topic_handler.get(event_name)

Answered By: Tomer Ariel

Any idea for a more elegant / simplest conditionnal return?

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