Conventions used

There are a number of text conventions used throughout this book.

CodeInText: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: "Let's check for the availability of GPIO packages using gpio_pkg_check.py and pip."

A block of code is set as follows:

# Global Variables
...
BROKER_HOST = "localhost"   # (2)
BROKER_PORT = 1883
CLIENT_ID = "LEDClient"     # (3)
TOPIC = "led"               # (4)
client = None # MQTT client instance. See init_mqtt()   # (5)
...

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

# Global Variables
...
BROKER_HOST = "localhost"   # (2)
BROKER_PORT = 1883
CLIENT_ID = "LEDClient"     # (3)
TOPIC = "led"               # (4)
client = None # MQTT client instance. See init_mqtt()   # (5)
...

Any command-line input or output is written as follows:

$ python --version
Python 2.7.16

Bold: Indicates a new term, an important word, or words that you see onscreen. For example, words in menus or dialog boxes appear in the text like this. Here is an example: "From your Raspbian desktop, navigate to the Raspberry menu | Preferences | Raspberry Pi Configuration."