OSX Python scripts

We are going to practice writing and running Python programs (often called "scripts").

Start your text editor

1. Launch the TextWrangler text editor. See the OS X text editor setup instructions for the steps to do this.
2. Start a new, blank text file.

Write and save a short Python script

1. Add the following line to your new text file:

print("Hello World!")

1. Save the script as hello.py in your home directory. The .py extension indicates that this file contains Python code.

Run the script

1. Start a terminal prompt. See the terminal navigation on OS X instructions for the steps to do this. A terminal prompt will look like $ and a Python prompt will look like >>>. Make sure you are at a terminal prompt and not a Python prompt; if you are at a Python prompt, you can type exit() on a line by itself and then press enter to exit Python and return to a terminal prompt.
2. Navigate to your home directory from a terminal prompt, using the ls, pwd, and cd commands. See the terminal navigation on OS X instructions for a refresher on using these commands. Don't hesitate to get help from a staff member on this step if you need it -- it's a new way of navigating your computer, so it may be unintuitive at first!
3. Once you are in your home directory, you'll see hello.py in the output of ls.
4. Type

python hello.py

and press enter. Doing this will cause Python to execute the contents of that script -- it should print "Hello World!" to the screen. What you've done here is run the Python application with an argument -- the name of a file, in this case "hello.py". Python knows that when you give it a file name as an argument, it should execute the contents of the provided file. You get the same result as if you typed

print("Hello World!")

at a Python prompt and press enter.

Success

You created and ran your first Python script!

• When you run the python command by itself, you start a Python prompt. You can execute Python code interactively at that prompt.
• When you run the python command with a file name as an argument, Python executes the Python code in that file.