Python Tutorial: Introduction to Data streams

Key Takeaways

welcome back in this lesson we'll learn how to subscribe to data streams using MQTT data streams are a constant stream of data examples of data streams include but are not limited to Twitter messages online news articles video streams such as this video sensor data or IOT and financial market orders this course will focus on sensor data from healthy devices we mentioned MQTT a couple of times already but what is it exactly n QT t or Message Queuing telemetry transport is a publish/subscribe messaging protocol designed to have a small footprint making it ideal for iot use cases an MQTT system consists of clients connecting to a server also called a broker these clients can publish or produce data to a topic and subscribe or consume data from or know multiple topics a topic is a string that the broker uses to filter messages for each connected client each topic can have multiple clients producing or consuming the same topic during this course will only act as a client subscribing to predefined topics assuming a producer is available in producing data will be using Eclipse paho and qtt Python client to connect to and PTT brokers the pipe modules are available in the package bajo dot MQTT more information and the documentation for the library is available under the project github page in the simplest case we only want one message from the broker this could be the case for other page showing the latest value available we can use subscribe that's simple for this which takes the topic as the first argument and the block has host name as the second argument and will return a message object we can then print the message topic as well as the message payload more often we want to receive a constant stream of data we are going to use a concept named callback to subscribe to a topic this is a very efficient way to wait for things to happen on the other end we do this by defining a callback function which will be called whenever a new message is available we are free to select any function name a recommended name is on message and will stick to that the header for a function used as the callback is defined by the PAHO dot MQTT library and needs to have the arguments client the client instance for the speaker back user data private user data set when creating the instance message an instance of MQTT message which is a class with the property's topic payload QoS and retain our arguments are mandatory even if we don't use them since the library calls the family to meet exactly these arguments within the function will print the topic of the message and the message payload separated by a column we now need to connect our function to an MQTT topic we'll import the module by hot mqtt dot subscribe and you subscribe to the callback with the function to be called as the first argument the topic to subscribe data camp / long term as the second argument and the server or broker as the keyword argument host name to connect a function to the topic the library will then connect to the MQTT broker and call our function each time a new message is available let's have a final look at a complete code first we import by hot mqtt dot subscribe a subscribe next we define our function on message and then pass this function as the first argument to subscribe that callback the topic name betacam slash room temp as the second argument and the host name for MK tts / as keyword argument host name once we run our program we will see the following output the topic on the left of the column as well as the message payload on the right which in this case is a JSON object containing the time temperature and humidity form an environmental sensor and now let's try this out