Merge pull request #4485 from hhunter-ms/issue_4424

add python to streaming subscriptions

Author: hhunter-ms

daprdocs/content/en/developing-applications/building-blocks/pubsub/subscription-methods.md

@@ -203,7 +203,112 @@ As messages are sent to the given message handler code, there is no concept of r
 
 The example below shows the different ways to stream subscribe to a topic.
 
-{{< tabs Go>}}
+{{< tabs Python Go >}}
+
+{{% codetab %}}
+
+You can use the `subscribe` method, which returns a `Subscription` object and allows you to pull messages from the stream by calling the `next_message` method. This runs in and may block the main thread while waiting for messages. 
+
+```python
+import time
+
+from dapr.clients import DaprClient
+from dapr.clients.grpc.subscription import StreamInactiveError
+
+counter = 0
+
+
+def process_message(message):
+    global counter
+    counter += 1
+    # Process the message here
+    print(f'Processing message: {message.data()} from {message.topic()}...')
+    return 'success'
+
+
+def main():
+    with DaprClient() as client:
+        global counter
+
+        subscription = client.subscribe(
+            pubsub_name='pubsub', topic='orders', dead_letter_topic='orders_dead'
+        )
+
+        try:
+            while counter < 5:
+                try:
+                    message = subscription.next_message()
+
+                except StreamInactiveError as e:
+                    print('Stream is inactive. Retrying...')
+                    time.sleep(1)
+                    continue
+                if message is None:
+                    print('No message received within timeout period.')
+                    continue
+
+                # Process the message
+                response_status = process_message(message)
+
+                if response_status == 'success':
+                    subscription.respond_success(message)
+                elif response_status == 'retry':
+                    subscription.respond_retry(message)
+                elif response_status == 'drop':
+                    subscription.respond_drop(message)
+
+        finally:
+            print("Closing subscription...")
+            subscription.close()
+
+
+if __name__ == '__main__':
+    main()
+
+```
+
+You can also use the `subscribe_with_handler` method, which accepts a callback function executed for each message received from the stream. This runs in a separate thread, so it doesn't block the main thread. 
+
+```python
+import time
+
+from dapr.clients import DaprClient
+from dapr.clients.grpc._response import TopicEventResponse
+
+counter = 0
+
+
+def process_message(message):
+    # Process the message here
+    global counter
+    counter += 1
+    print(f'Processing message: {message.data()} from {message.topic()}...')
+    return TopicEventResponse('success')
+
+
+def main():
+    with (DaprClient() as client):
+        # This will start a new thread that will listen for messages
+        # and process them in the `process_message` function
+        close_fn = client.subscribe_with_handler(
+            pubsub_name='pubsub', topic='orders', handler_fn=process_message,
+            dead_letter_topic='orders_dead'
+        )
+
+        while counter < 5:
+            time.sleep(1)
+
+        print("Closing subscription...")
+        close_fn()
+
+
+if __name__ == '__main__':
+    main()
+```
+
+[Learn more about streaming subscriptions using the Python SDK client.]({{< ref "python-client.md#streaming-message-subscription" >}})
+
+{{% /codetab %}}
 
 {{% codetab %}}