code: def rollback_lambda_function_version(self, function_name, versions_back=1, publish=True):
          
          response = self.lambda_client.list_versions_by_function(FunctionName=function_name)
  
          # Take into account $LATEST
          if len(response['Versions']) < versions_back + 1:
              print("We do not have {} revisions. Aborting".format(str(versions_back)))
              return False
  
          revisions = [int(revision['Version']) for revision in response['Versions'] if revision['Version'] != '$LATEST']
          revisions.sort(reverse=True)
  
          response = self.lambda_client.get_function(FunctionName='function:{}:{}'.format(function_name, revisions[versions_back]))
          response = requests.get(response['Code']['Location'])
  
          if response.status_code != 200:
              print("Failed to get version {} of {} code".format(versions_back, function_name))
              return False
  
          response = self.lambda_client.update_function_code(FunctionName=function_name, ZipFile=response.content, Publish=publish)  # pragma: no cover
  
          return response['FunctionArn']
docs: Rollback the lambda function code 'versions_back' number of revisions.
  
          Returns the Function ARN.