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| We are going to practice writing and running Python programs (often called "scripts").
| | #redirect [[Python scripts in Jupyter]] |
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| ===Start your text editor===
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| # Launch the TextWrangler text editor. See the [[OSX text editor|OS X text editor setup]] instructions for the steps to do this. | |
| # Start a new, blank text file.
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| ===Write and save a short Python script===
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| # Add the following line to your new text file:
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| <pre>
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| print("Hello World!")
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| </pre>
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| # Save the script as <code>hello.py</code> in your home directory. The <code>.py</code> extension indicates that this file contains Python code.
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| ===Run the script===
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| # Start a terminal prompt. See the [[OSX terminal navigation|terminal navigation on OS X]] instructions for the steps to do this. A terminal prompt will look like <code>$</code> and a Python prompt will look like <code>>>></code>. Make sure you are at a terminal prompt and not a Python prompt. If you are at a Python prompt, you can type <code>exit()</code> on a line by itself and then press enter to exit Python and return to a terminal prompt.
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| # Navigate to your home directory from a terminal prompt, using the <code>ls</code>, <code>pwd</code>, and <code>cd</code> commands. See the [[OSX terminal navigation|terminal navigation on OS X]] instructions for a refresher on using these commands. Don't hesitate to get help from a mentor on this step if you need it -- it's a new way of navigating your computer, so it may be unintuitive at first!
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| # Once you are in your home directory, you'll see <code>hello.py</code> in the output of <code>ls</code>.
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| # Type
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| <pre>
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| python hello.py
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| </pre>
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| 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
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| <pre>
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| print("Hello World!")
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| </pre>
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| at a Python prompt and press enter.
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| ===Success===
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| You created and ran your first Python script!
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| * When you run the <code>python</code> command by itself, you start a Python prompt. You can execute Python code interactively at that prompt.
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| * When you run the <code>python</code> command with a file name as an argument, Python executes the Python code in that file.
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| [[File:Champagne.png|100px]][[File:Party.png|125px]]
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| [[Category:CDSW]]
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