So, now this is one way to write a program.
We just wrote one by typing a series of commands to the interpreter but
if we wanted to run that program again, we don't have it.
We've just typed it in.
We'd have to type it in again.
That's not a very effective way to do programming.
So of course, most of the time when you do programming,
you're going to write your program in a file and then take that file and
interpret the entire file or pass that file to the Python interpreter.
So here's the same commands.
We can store them in a file.
We can call that file say gc.py.
You can give it any name you want.
And we just put exactly those commands that we just typed in interpreter.
Put them all in a file, just a plain text file.
And the extension .py by the way is a convention
that is usually used to indicate that our files contains a python program.
It doesn't have to have that but it is really helpful if you use that.
And that way you can keep track of all the files that you have
that are python programs rather than, say, text files or word documents or
presentations of some kind.
So now we got this file, we want to execute this file.
So we don't to have to type it in again,
we want to be able to take this entire file and run it in Python.
So we can pass this file to the Python interpreter.
We could do that by typing in the name Python itself, that's the Python program,
rather than typing Python and just letting it give us back the prompt,
we can type in Python and give it the name of our program here, gc.py.
And that tells Python take this file and
execute what's in it and it will give us the answer, 53.06%.
So you might not want to type Python and then your program name every time.
So instead of doing that, you can just embed in the file itself a special command
or a special line that tells the computer that what this program is,
is a Python program.
So if you put this special path name as the very first line of your file,
which is #!/users/bin/python which is the path to python on my computer.
You put that as your first line of your program then that when you try to run this
file to the UNIX command line prop the UNIX system itself will look at that first
line and say oh this is a python program I'm going to call the python interpreter.
So you don't have to type python, you can just type gc.py and
that will run the program.
Now once you put that special line and it's the first line of your python file,
which you will do for all your files from now on.
You just type gc.py and it will run the program.
And the reason I put ./gcpy was I was telling the UNIX command line to look in
the directory I am in right now which is where this file is.
