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As we go through the examples in this course, and as you look at scripts that you

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find from different sources, and as you write your own scripts, you are going to

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notice a few things that are constant in how these scripts are constructed.

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If we look at the syntax.py file here in our 04 Syntax folder in Exercise Files,

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you will notice a few things.

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First of all, at the very top, there is this line with a Pound sign, which is

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the Comment Indicator in Python and an exclamation point and then a path to

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the Python Interpreter.

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This is used in environments that run the script from a shell, UNIX-based

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environments like a Mac or Linux environment, and one of the beauties of a

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scripting language like Python is that your script can run in a number of

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different environments without change.

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So it's important that you leave this as the first line of the file.

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Now this path here that starts with the first slash must be the path to

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the Python Interpreter.

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Now this is a very common path: /user/bin/ python3, that will work in a lot of environments.

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If you try to run this in UNIX- based environments and you find that it

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doesn't work, one thing that you'll want to look at is this path to see if the

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path needs to change.

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Another thing that you will notice is this line down here at the end.

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What this does is it allows us to run the script with the functions in any

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order that we want.

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Without this line and without the main execution of the script being inside a

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function called main, then you wouldn't be able to run functions that are

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defined after the function is called.

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In other words, if I put a function in here, and I say def egg():

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and print("egg") now I'll need to call the egg here, egg() and save and run,

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you will notice that that runs.

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Now if I were to take out this def main

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and just make this like that without it being in any function at all, and we will

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get rid of this, so you might want to just call egg from here and then define

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egg down there, that will not work.

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That will give us a syntax error because egg is not defined at the point where we call it.

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So what this allows us to do is to define functions after they are called, and

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this is actually very useful and very common, so you will see this construct in a

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lot of the scripts that you encounter.

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If we just have it this way, it would serve the same purpose.

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The reason for this part of it here is it allows this to only be run when this

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file is called as the main module.

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Later on in the course, we will get into writing modules, and modules typically

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contain classes and functions.

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A lot of times when you write a module you are going to want to have a test

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suite at the end of the module, and this allows you to put that in a main

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function, and it will only run if the module is called as the main module.

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It won't run when the module is included in other modules.

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So you will see this pattern a lot, and that's basically what it does and what

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it's for, and it's just a good idea to always stick it in your scripts.