4 - Python Scripting

What are we learning?

In this lesson we will:

• Learn how to apply 'permanent' settings to BASH and Nano with run commands (.bashrc and .nanorc)

• Confirm we have Python installed

• Discuss an argument vector (argv)

• Compare BASH to Python with the treats script

Run Commands

When you give arguments to a program that modify how the program works, these are sometimes called run commands. Some programs can store these options in a configuration file.
.bashrc

• Let's edit the .bashrc file:  nano .bashrc

• Look for the lines containing "PS1" - use your ability to read code to discern what those mean / do

  • Feel free to customize yours to your liking (there's lots of details online)

.nanorc

Nano can also take run commands to modify how it works. 

• Try:  man nano

Let's change tabs to spaces and a couple other things...

• Make a new file in your home folder:
  cd ~
  nano .nanorc

• A couple personal preferences:
  set tabstospaces
  set tabsize 4
  set linenumbers
  set mouse

• Save and exit... restart nano to take a look

Python

BASH is powerful but it's more of an operating system scripting language - for talking to the kernel, making and reading files, etc... What if we want to write a program that is cross-platform and portable-ish?

Python is the Swiss army knife of scripting languages. It's not amazing at one thing - it's pretty good at all things. It's also a popular platform for learning, data analysis, and sharing libraries of code that do cool things.

Let's check if Python is installed:

• python

• Don't worry - it's actually there...  python3

  • type exit() to get out of the interpreter

• Let's create a system-wide alias for python3:  sudo install python-is-python3

Python Treats

Let's recreate the Dog Treats program we wrote in BASH:

• Create the script treats.py and add a shebang line at the top (where is the python executable?)

• Make your script executable in Linux

• We want to run the program like this:  ./treats.py 3 2 1   (or similar)

  • How do we get command-line arguments in Python?

    • When you give arguments to a program they are placed in an argument vector (a list or array)

    • In Python, we need to import the sys module to get access to system information - including the argument vector argv
      import sys

    • Now the list of arguments can be read through the list sys.argv

  • Can we successfully use Python to recreate the treats program?

Zero That Out

In the EXTRAS section of the first class task was the description of a boss who would give numbers to sum but if the boss made a mistake they would say the number zero meaning to not use the last number. Can we recreate the program in Python? Would this be easier than in BASH?

Reference:  Python Tutorial (w3)