Barebones AWS Lambda code to update a user's tags in Mailchimp

aws_lambda_sns_update_mailchimp.py

import json
import hashlib
import urllib3

API_KEY = "[API-KEY]"
DC = "us19"
LIST_ID = "[AUDIENCE]"
TAG = 'core'

http = urllib3.PoolManager()

def update_user(email):
    hash = hashlib.md5(email.encode('utf-8')).hexdigest()
    headers = urllib3.make_headers(basic_auth=f'foo:{API_KEY}')
    encoded_data = json.dumps({"tags": [{"name": TAG, "status": "active"}]}).encode('utf-8')
    r = http.request('POST',
                     f'https://{DC}.api.mailchimp.com/3.0/lists/{LIST_ID}/members/{hash}/tags',
                     body=encoded_data,
                     headers=headers)  
    return r.data.decode('utf-8')
    
    
def lambda_handler(event, context):
    users = []
    for rec in event['Records']:
        # Assuming SNS Message = "email1, ..., emailN"
        for email in rec['Sns']['Message'].split(','):
            if len(email) > 0:
                update_user(email.strip())
                users.append(f"Added tag:{TAG} to user:{email}")
    
    return {
        'statusCode': 200,
        'body': json.dumps(users)
    }