问UpdateExpression调用update_item，错误:无效Lambda :运算符或函数的操作数类型不正确；运算符或函数：+，操作数类型:m

EN

import boto3
import json


def handler(event, context):
    '''Provide an event that contains the following keys:

      - operation: one of the operations in the operations dict below
      - tableName: required for operations that interact with DynamoDB
      - payload: a parameter to pass to the operation being performed
    '''

    operation = event['operation']

    if 'tableName' in event:
        dynamo = boto3.resource('dynamodb').Table(event['tableName'])

    operationsDict = {
        'create': lambda x: dynamo.put_item(**x),
        'read': lambda x: dynamo.get_item(**x),
        'update': lambda x: dynamo.update_item(**x),
        'delete': lambda x: dynamo.delete_item(**x),
        'list': lambda x: dynamo.scan(**x),
        'echo': lambda x: x,
        'ping': lambda x: 'pong'
    }

    if operation in operationsDict:
        return operationsDict[operation](event.get('payload'))
    else:
        raise ValueError('Unrecognized operation "{}"'.format(operation))

{
  "operation": "update",
  "tableName": "CCDynamoDB",
  "payload": {
    "Key": {
            "id": {"S":"visitorCount"}
        },
        "UpdateExpression": "SET #7c680 = #7c680 + :7c680",
        "ExpressionAttributeNames": {"#7c680":"currentCount"},
        "ExpressionAttributeValues": {":7c680": {"N":"1"}}
  }
}