lambda.py

import json
import boto3
from decimal import Decimal as D

dynamodb = boto3.resource('dynamodb', region_name="eu-west-1")
s3 = boto3.client('s3')

class DecimalEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, D):
            return float(obj)
        return json.JSONEncoder.default(self, obj)

def list(event, context):

    keys = []
    resp = s3.list_objects_v2(Bucket='imgur-serverless')
    for obj in resp['Contents']:
        keys.append(obj['Key'])

    response = {
        "statusCode": 200,
        "body": json.dumps(keys, cls=DecimalEncoder),
        'headers': {
            'Content-Type': 'application/json',
            'Access-Control-Allow-Origin': '*'
        },
    }

    return response