Template:Chicago Python Workshop/Setup/Mac Python scripts

From OpenHatch wiki

We are going to practice writing and running Python scripts.

Start your text editor

  1. Launch the Smultron 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 command prompt. See the terminal navigation on OS X instructions for the steps to do this. Recall that a terminal prompt will look like jesstess$ 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 hit enter to exit Python and return to a terminal prompt.
  2. Navigate to your home directory from a command 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 hit 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 hit 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.
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