Pub/Sub: improve pub.py (#2403)

* print number of messages published

* two nit's

Author: anguillanneuf

pubsub/cloud-client/quickstart/pub.py

@@ -22,13 +22,13 @@
 # [END pubsub_quickstart_pub_deps]
 
 
-def get_callback(api_future, data):
+def get_callback(api_future, data, ref):
     """Wrap message data in the context of the callback function."""
-
     def callback(api_future):
         try:
             print("Published message {} now has message ID {}".format(
                 data, api_future.result()))
+            ref["num_messages"] += 1
         except Exception:
             print("A problem occurred when publishing {}: {}\n".format(
                 data, api_future.exception()))
@@ -39,24 +39,28 @@ def callback(api_future):
 def pub(project_id, topic_name):
     """Publishes a message to a Pub/Sub topic."""
     # [START pubsub_quickstart_pub_client]
-    # Initialize a Publisher client
+    # Initialize a Publisher client.
     client = pubsub_v1.PublisherClient()
     # [END pubsub_quickstart_pub_client]
     # Create a fully qualified identifier in the form of
     # `projects/{project_id}/topics/{topic_name}`
     topic_path = client.topic_path(project_id, topic_name)
 
-    # Data sent to Cloud Pub/Sub must be a bytestring
+    # Data sent to Cloud Pub/Sub must be a bytestring.
     data = b"Hello, World!"
 
+    # Keep track of the number of published messages.
+    ref = dict({"num_messages": 0})
+
     # When you publish a message, the client returns a future.
     api_future = client.publish(topic_path, data=data)
-    api_future.add_done_callback(get_callback(api_future, data))
+    api_future.add_done_callback(get_callback(api_future, data, ref))
 
-    # Keep the main thread from exiting until background message
-    # is processed.
+    # Keep the main thread from exiting while the message future
+    # gets resolved in the background.
     while api_future.running():
-        time.sleep(0.1)
+        time.sleep(0.5)
+        print("Published {} message(s).".format(ref["num_messages"]))
 
 
 if __name__ == '__main__':