对更优雅/最简单的条件返回有任何想法吗？答案

【问题标题】：Any idea for a more elegant / simplest conditionnal return?对更优雅/最简单的条件返回有任何想法吗？
【发布时间】：2022-11-14 09:25:31
【问题描述】：

这是python代码：

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

它有效，但我正在寻找一种更有效/优雅/最简单的方法来做同样的事情。如果你有任何想法，我会接受的：）。

【问题讨论】：

标签： python

【解决方案1】：

我会像这样重构你的代码，所以它不那么拥挤，而且只有一个返回点（所以控制流更容易检查）。

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

【讨论】：

我也喜欢这种方法。有很多方法可以做到这一点。

【解决方案2】：

你也可以做类似的事情

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)

【讨论】：

【解决方案3】：

你可以使用一个字典避免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)

由于如果状态不是CANCELLED，该函数也可以返回None，因此字典在设置键CONFIG.get("FOX_ORDER_RESULTS_SNS_TOPIC_ARN") 的值时会考虑到这一点。

此外，如果topic_arn 不存在，您可以自定义将返回的内容。为此，只需将默认返回值传递给handlers.get(topic_arn)，如下所示：

handlers.get(topic_arn, "NOT FOUND")

【讨论】：

【解决方案4】：

这是一种使用handler 映射和validator 映射的方法，可将验证逻辑与处理逻辑分离：

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)

【讨论】：