Add listen for errors sample. [(#1306)](GoogleCloudPlatform/python-do…

…cs-samples#1306)

* Add listen for errors sample.

* Update subscriber.py

* Update subscriber.py

samples/snippets/subscriber.py

@@ -110,6 +110,30 @@ def callback(message):
  time.sleep(60)
 
 
+def listen_for_errors(project, subscription_name):
+ """Receives messages and catches errors from a pull subscription."""
+ subscriber = pubsub_v1.SubscriberClient()
+ subscription_path = subscriber.subscription_path(
+ project, subscription_name)
+
+ def callback(message):
+ print('Received message: {}'.format(message))
+ message.ack()
+
+ subscription = subscriber.subscribe(subscription_path, callback=callback)
+
+ # Blocks the thread while messages are coming in through the stream. Any
+ # exceptions that crop up on the thread will be set on the future.
+ future = subscription.open(callback)
+ try:
+ future.result()
+ except Exception as e:
+ print(
+ 'Listening for messages on {} threw an Exception: {}.'.format(
+ subscription_name, e))
+ raise
+
+
 if __name__ == '__main__':
  parser = argparse.ArgumentParser(
  description=__doc__,
@@ -143,6 +167,10 @@ def callback(message):
  help=receive_messages_with_flow_control.__doc__)
  receive_with_flow_control_parser.add_argument('subscription_name')
 
+ listen_for_errors_parser = subparsers.add_parser(
+ 'listen_for_errors', help=listen_for_errors.__doc__)
+ listen_for_errors_parser.add_argument('subscription_name')
+
  args = parser.parse_args()
 
  if args.command == 'list_in_topic':
@@ -160,3 +188,5 @@ def callback(message):
  elif args.command == 'receive-flow-control':
  receive_messages_with_flow_control(
  args.project, args.subscription_name)
+ elif args.command == 'listen_for_errors':
+ listen_for_errors(args.project, args.subscription_name)