Add simple MQTT subscription example.

Author: tdicola

examples/mqtt_client.py

@@ -10,8 +10,8 @@
 from Adafruit_IO import MQTTClient
 
 
-# Set to your Adafruit IO key.
-ADAFRUIT_IO_KEY = 'YOUR ADAFRUIT IO KEY'
+# Set to your Adafruit IO key & username below.
+ADAFRUIT_IO_KEY      = 'YOUR ADAFRUIT IO KEY'
 ADAFRUIT_IO_USERNAME = 'YOUR ADAFRUIT IO USERNAME'  # See https://accounts.adafruit.com
                                                     # to find your username.
 

examples/mqtt_subscribe.py

@@ -0,0 +1,57 @@
+# Example of using the MQTT client class to subscribe to a feed and print out
+# any changes made to the feed.  Edit the variables below to configure the key,
+# username, and feed to subscribe to for changes.
+
+# Import standard python modules.
+import sys
+
+# Import Adafruit IO MQTT client.
+from Adafruit_IO import MQTTClient
+
+
+# Set to your Adafruit IO key & username below.
+ADAFRUIT_IO_KEY      = 'YOUR ADAFRUIT IO KEY'
+ADAFRUIT_IO_USERNAME = 'YOUR ADAFRUIT IO USERNAME'  # See https://accounts.adafruit.com
+                                                    # to find your username.
+
+# Set to the ID of the feed to subscribe to for updates.
+FEED_ID = 'DemoFeed'
+
+
+# Define callback functions which will be called when certain events happen.
+def connected(client):
+    # Connected function will be called when the client is connected to Adafruit IO.
+    # This is a good place to subscribe to feed changes.  The client parameter
+    # passed to this function is the Adafruit IO MQTT client so you can make
+    # calls against it easily.
+    print 'Connected to Adafruit IO!  Listening for {0} changes...'.format(FEED_ID)
+    # Subscribe to changes on a feed named DemoFeed.
+    client.subscribe(FEED_ID)
+
+def disconnected(client):
+    # Disconnected function will be called when the client disconnects.
+    print 'Disconnected from Adafruit IO!'
+    sys.exit(1)
+
+def message(client, feed_id, payload):
+    # Message function will be called when a subscribed feed has a new value.
+    # The feed_id parameter identifies the feed, and the payload parameter has
+    # the new value.
+    print 'Feed {0} received new value: {1}'.format(feed_id, payload)
+
+
+# Create an MQTT client instance.
+client = MQTTClient(ADAFRUIT_IO_USERNAME, ADAFRUIT_IO_KEY)
+
+# Setup the callback functions defined above.
+client.on_connect    = connected
+client.on_disconnect = disconnected
+client.on_message    = message
+
+# Connect to the Adafruit IO server.
+client.connect()
+
+# Start a message loop that blocks forever waiting for MQTT messages to be
+# received.  Note there are other options for running the event loop like doing
+# so in a background thread--see the mqtt_client.py example to learn more.
+client.loop_blocking()