lambdaを使ってSNSのアクセスポリシーを取得、変更、更新したいのですが、更新の部分set_topic_attributesが上手くいきません
解決方法を教えて頂きたいです。

py
import os
import boto3
import json
import ast

import logging
logger = logging.getLogger()
logger.setLevel(logging.INFO)

topic_arn = os.environ['topic_arn']
account_no = os.environ['account_no']

sns_client = boto3.client('sns')

def lambda_handler(event, context):

    # snsポリシー取得
    sns_policy = get_sns_policy(sns_client, topic_arn)
    print('sns_policy:',sns_policy)
    
    if sns_policy != 'policy_not_exist':
        # ポリシーの中に'S3-Events'があるかチェック
        check_policy_result = check_policy(sns_policy)
        print('check_policy_result:',check_policy_result)

        if not check_policy_result:
            # snsポリシー修正
            new_sns_policy = mod_sns_policy(sns_policy, topic_arn, account_no)
            print('new_sns_policy:',new_sns_policy)
            
            # 修正したポリシーをsnsにアプデ
            update_sns_policy(sns_client, new_sns_policy, topic_arn)


    
    
def get_sns_policy(sns_client, topic_arn):
    try:
        response = sns_client.get_topic_attributes(TopicArn=topic_arn)
        return ast.literal_eval(response['Attributes']['Policy'])
    except Exception:
        return 'policy_not_exist'

    
def check_policy(sns_policy):
    print(type(sns_policy))
    s3_events_flg = False
    for statement in sns_policy['Statement']:
        # キー"Sid"がある場合　かつ　値が "S3-Events"の場合
        if "Sid" in statement.keys() and statement["Sid"] == "S3-Events":
            print('S3-Events Yes it is')
            s3_events_flg = True
            return s3_events_flg
        else: print('S3-Events No it isnt')
    return s3_events_flg
    
    
def mod_sns_policy(sns_policy, topic_arn, account_no):
    print('mod_sns_policy_function')

    new_statement = {
        "Sid": "S3-Events","Effect": "Allow",
        "Principal": {"Service": "s3.amazonaws.com"},
        "Action": "sns:Publish",
        "Resource": topic_arn,
        "Condition": {"StringEquals": { "AWS:SourceAccount": account_no }}
    }
    sns_policy['Statement'].append(new_statement)
    
    return sns_policy


def update_sns_policy(sns_client, new_sns_policy, topic_arn):
    print('update_sns_policy_function')
    
    jsondumps_new_sns_policy = json.dumps(new_sns_policy)
    str_new_sns_policy = str(new_sns_policy)

    try:
        sns_client.set_topic_attributes(
            TopicArn=topic_arn,
            AttributeName='DeliveryPolicy',
            AttributeValue=str_new_sns_policy
        )
    except Exception as e:
        logger.error(e)

Lambda設定

ライタイム：Python 3.9
アーキテクチャ：x86_64

試したこと

sns_client.set_topic_attributes()のAttributeValue=に入る部分を、json.dumpsやstrなどの形に変換して試してみました。

new_sns_policy (pythonのdict形式のまま)の場合

[ERROR]	2022-03-20T12:57:40.342Z	11dd47c8-2cb7-4240-a382-74a016619469	Parameter validation failed:
Invalid type for parameter AttributeValue, value: { ポリシー の中身(割愛) }, type: <class 'dict'>, valid types: <class 'str'>

json.dumps(new_sns_policy) の場合

[ERROR]	2022-03-20T12:25:00.778Z	eac745dd-e649-492d-b551-bab8bb62fcb6	An error occurred (InvalidParameter) when calling the SetTopicAttributes operation: Invalid parameter: DeliveryPolicy: Unexpected JSON member: Version

str(new_sns_policy)の場合

[ERROR]	2022-03-20T12:54:13.830Z	404be517-147f-4fe8-929a-6788049c068c	An error occurred (InvalidParameter) when calling the SetTopicAttributes operation: Invalid parameter: DeliveryPolicy: Invalid JSON: Unexpected character (''' (code 39)) at [line: 1, column: 3]: was expecting double-quote to start field name