c157-example2.py

"""
Example 2

Introducing both kinds of comments, and using them to explain in detail the 
elements of Example 1. 
"""

# A 'comment' is code that is ignored by a language's compiler or interpreter. 
# Python ignores any line that starts with the octothorpe (`#`). 
# You might be more familiar with the term 'hash' or 'pound sign' for the # character.

"""
Another way to write comments is by surrounding a block of text with three 
quote characters--three on top, and three on the bottom. 

Multi-line comments are useful when you have a LOT of text to write and don't 
want to put a # symbol in front of every single line.

It doesn't matter which kind of comment syntax you use, but generally speaking, 
use the octothorpe symbol for single-line comments and the triple-quote comments 
for multi-line comments.
"""

"""
The 'import' statement is used to import functionality from a 'module' called 
'sys' (short for 'system'). The 'sys' module provides some very low-level 
information about Python's interpreter, and lets us use the sys.exit() 
function later.
"""
import sys

# This block "defines" (def) a function named 'main'. We know it's a function 
# because it has the parentheses ( and ). 
def main():
  # Note how we indented here. This means that anything at this level of 
  # indentation is part of the 'main' function's scope.
  
  # The print function simply prints a string to the window where we are running
  # the Python interpreter.
  print("Hello, World!")

  # Because the below print statement is commented out, it will not execute.
  # print("I am a donut")

  # Comments do not follow indentation/scope rules, but it's a good idea to 
  # keep them indented with the scope in which you are making the comment. 

  # Comments 
    # like 
      # this 
        # are
          # technically legal, 
            # but will make
              # everyone around you
                # very frustrated!

"""
Below is a standard application initialization block of code, found in 
thousands of files across thousands of applications. It's purpose is to 
pass the main function of our program into Python's sys.exit() function, which 
allows Python to 'catch' errors in a more efficient manner. 

You do not need to understand this yet, but you should be familiar with it--
you will be seeing it a lot!
 
Learn more on your own: https://stackoverflow.com/a/5280221
"""
if __name__ == '__main__':
  sys.exit(main())