Pub/Sub: wrap subscriber in a with block and add comments [(#4070)](GoogleCloudPlatform/python-docs-samples#4070)

Use a `with` block to wrap subscriber and describe its purpose. 

Internal bug: b/157401623

Author: anguillanneuf

samples/snippets/subscriber.py

@@ -52,10 +52,11 @@ def list_subscriptions_in_project(project_id):
     subscriber = pubsub_v1.SubscriberClient()
     project_path = subscriber.project_path(project_id)
 
-    for subscription in subscriber.list_subscriptions(project_path):
-        print(subscription.name)
-
-    subscriber.close()
+    # Wrap the subscriber in a 'with' block to automatically call close() to
+    # close the underlying gRPC channel when done.
+    with subscriber:
+        for subscription in subscriber.list_subscriptions(project_path):
+            print(subscription.name)
     # [END pubsub_list_subscriptions]
 
 
@@ -73,11 +74,12 @@ def create_subscription(project_id, topic_id, subscription_id):
     topic_path = subscriber.topic_path(project_id, topic_id)
     subscription_path = subscriber.subscription_path(project_id, subscription_id)
 
-    subscription = subscriber.create_subscription(subscription_path, topic_path)
+    # Wrap the subscriber in a 'with' block to automatically call close() to
+    # close the underlying gRPC channel when done.
+    with subscriber:
+        subscription = subscriber.create_subscription(subscription_path, topic_path)
 
     print("Subscription created: {}".format(subscription))
-
-    subscriber.close()
     # [END pubsub_create_pull_subscription]
 
 
@@ -146,14 +148,15 @@ def create_push_subscription(project_id, topic_id, subscription_id, endpoint):
 
     push_config = pubsub_v1.types.PushConfig(push_endpoint=endpoint)
 
-    subscription = subscriber.create_subscription(
-        subscription_path, topic_path, push_config
-    )
+    # Wrap the subscriber in a 'with' block to automatically call close() to
+    # close the underlying gRPC channel when done.
+    with subscriber:
+        subscription = subscriber.create_subscription(
+            subscription_path, topic_path, push_config
+        )
 
     print("Push subscription created: {}".format(subscription))
     print("Endpoint for subscription is: {}".format(endpoint))
-
-    subscriber.close()
     # [END pubsub_create_push_subscription]
 
 
@@ -169,11 +172,12 @@ def delete_subscription(project_id, subscription_id):
     subscriber = pubsub_v1.SubscriberClient()
     subscription_path = subscriber.subscription_path(project_id, subscription_id)
 
-    subscriber.delete_subscription(subscription_path)
+    # Wrap the subscriber in a 'with' block to automatically call close() to
+    # close the underlying gRPC channel when done.
+    with subscriber:
+        subscriber.delete_subscription(subscription_path)
 
     print("Subscription deleted: {}".format(subscription_path))
-
-    subscriber.close()
     # [END pubsub_delete_subscription]
 
 
@@ -203,12 +207,13 @@ def update_push_subscription(project_id, topic_id, subscription_id, endpoint):
 
     update_mask = {"paths": {"push_config"}}
 
-    result = subscriber.update_subscription(subscription, update_mask)
+    # Wrap the subscriber in a 'with' block to automatically call close() to
+    # close the underlying gRPC channel when done.
+    with subscriber:
+        result = subscriber.update_subscription(subscription, update_mask)
 
     print("Subscription updated: {}".format(subscription_path))
     print("New endpoint for subscription is: {}".format(result.push_config))
-
-    subscriber.close()
     # [END pubsub_update_push_configuration]
 
 
@@ -436,24 +441,25 @@ def synchronous_pull(project_id, subscription_id):
 
     NUM_MESSAGES = 3
 
-    # The subscriber pulls a specific number of messages.
-    response = subscriber.pull(subscription_path, max_messages=NUM_MESSAGES)
+    # Wrap the subscriber in a 'with' block to automatically call close() to
+    # close the underlying gRPC channel when done.
+    with subscriber:
+        # The subscriber pulls a specific number of messages.
+        response = subscriber.pull(subscription_path, max_messages=NUM_MESSAGES)
 
-    ack_ids = []
-    for received_message in response.received_messages:
-        print("Received: {}".format(received_message.message.data))
-        ack_ids.append(received_message.ack_id)
+        ack_ids = []
+        for received_message in response.received_messages:
+            print("Received: {}".format(received_message.message.data))
+            ack_ids.append(received_message.ack_id)
 
-    # Acknowledges the received messages so they will not be sent again.
-    subscriber.acknowledge(subscription_path, ack_ids)
+        # Acknowledges the received messages so they will not be sent again.
+        subscriber.acknowledge(subscription_path, ack_ids)
 
-    print(
-        "Received and acknowledged {} messages. Done.".format(
-            len(response.received_messages)
+        print(
+            "Received and acknowledged {} messages. Done.".format(
+                len(response.received_messages)
+            )
         )
-    )
-
-    subscriber.close()
     # [END pubsub_subscriber_sync_pull]
 
 
@@ -539,6 +545,8 @@ def worker(msg):
         )
     )
 
+    # Close the underlying gPRC channel. Alternatively, wrap subscriber in
+    # a 'with' block to automatically call close() when done.
     subscriber.close()
     # [END pubsub_subscriber_sync_pull_with_lease]