Python-AWS Lambda从CloudWatch事件JSON提取字段报错求助

Hey there! Let's break down what's going wrong here and get your function working properly.

The Root Issue #

The Message field from your SNS record is a JSON-formatted string, not a native Python dictionary. When you try to access ['Trigger'] directly on this string, Python throws that error because strings only accept numeric indices (like message[0] to grab the first character), not key names.

The Fix #

You need to first parse that JSON string into a Python dictionary using json.loads(). Once it's converted, you can access the nested keys normally. Also, keep in mind that Dimensions is likely a list of objects, so you'll need to index into that list before grabbing the name field.

Corrected Code #

Here's the updated function with clear comments explaining each step:

import json
def lambda_handler(event, context):
    print("Received event: " + json.dumps(event, indent=2))
    
    # Pull the raw JSON string from the SNS message
    sns_message_str = event['Records'][0]['Sns']['Message']
    
    # Convert the JSON string into a usable Python dictionary
    sns_message_dict = json.loads(sns_message_str)
    
    # Optional: Print the parsed dictionary to confirm the structure matches your expectations
    print("Parsed SNS message: " + json.dumps(sns_message_dict, indent=2))
    
    # Access the nested 'name' field (use [0] to get the first dimension; adjust if you have multiple)
    dimension_name = sns_message_dict['Trigger']['Dimensions'][0]['name']
    print(f"Extracted dimension name: {dimension_name}")
    
    return {
        'statusCode': 200,
        'body': json.dumps({'extractedDimensionName': dimension_name})
    }

Quick Tips #

• If your Dimensions list has multiple entries, loop through them instead of using [0] to collect all name values.
• Use the optional print statement for the parsed dictionary to double-check key names and structure—typos or unexpected nesting are common pitfalls here.

内容的提问来源于stack exchange，提问作者TheDataGuy