title: AWS Lambda is unable to find a SNS topic that clearly exists?
body: <p>I create an SNS topic via the console. Then tried to call <code>list_subscriptions_by_topic</code> or <code>sns.publish</code> but they failed with this message:</p>
  <pre><code>    An error occurred (NotFound) when calling the Publish 
      operation: Topic does not exist: NotFoundException
  </code></pre>
  <p>The topic is accessible in the SNS console. Any idea why is can't be found?</p>
  <p>This is my lambda code:</p>
  <pre class="lang-py prettyprint-override"><code>    from __future__ import print_function
      
      import json
      import boto3
      import random
      
      
      print('Loading function')
      sns = boto3.client('sns')
      
      def lambda_handler(event, context):
          
          response = sns.publish(
              TopicArn='arn:aws:sns:us-west-2:031436316123:topicExists' 
              Message=json.dumps(newMsg),
              MessageAttributes={
                  'event_type':{
                      'DataType':'String', 'StringValue':'something'
                      
                  }
              }
          )
      
          return response
  </code></pre>
  <p>It is a Lambda trigger set on an SQS that is subscribed to <code>topicExists</code> SNS topic.</p>