These variables are important for executing scripts written in Python, not for writing them. If they are not configured, the location of the Python binary has to be referenced by its fully qualified path location. As an example, here is the execution of a Python script without the environmental variable being declared in Windows:

C:\Python27\python wargames_print.py

The following is the equivalent in Linux or Unix if the reference to the proper interpreter is not listed at the top of the script and the file is in your current directory:

/usr/bin/python ./wargames_print.py

In Windows, if the environmental variable is set, you can simply execute the script by typing python and the script name. In Linux and Unix, we add a line at the top of the script to make it more portable. A benefit to us (penetration testers) is that this makes the script useful on many different types of systems, including Windows. This line is ignored by the Windows operating system natively...