Add some comments

Messaging/mqttsession.py

@@ -3,8 +3,13 @@ import paho.mqtt.client as mqtt
 client = None
 host = None
 
+"""
+Wrapper module for paho mqtt library, providing a singleton instance of the client to be used. 
+"""
+
 # Arguably not needed, just want to make the client static, but here anyway.
 def connect():
+    global client
     if client is None or host is None:
         print("Error: Client and/or host are not initialised.")
     else:
@@ -12,6 +17,7 @@ def connect():
         client.loop_start()
 
 def disconnect():
+    global client
     if client is not None:
         client.loop_stop()
         client.disconnect()
@@ -19,7 +25,8 @@ def disconnect():
         print("Error: Client is not initialised.")
 
 def Client():
-    if client is not None:
-        return mqtt.Client()
-    else:
+    global client
+    if client is None:
+        client =  mqtt.Client()
+
     return client