Session on Python, a general-purpose programming language used for a wide variety of computational tasks.
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So far, you’ve interacted with Python one line at a time in the REPL. For the rest of this session, we’re going to write and execute longer programs.
Open your text editor of choice (such as VS Code) and create a new file with this line:
print("Hello world!")
Save it with the name hello.py to a known location, such as your desktop. Open your terminal and move to the desktop directory:
$ cd Desktop
Once you’re in the folder with your hello.py file, run it with:
$ python hello.py
Hello world!
As above, you should see the text Hello world! appear as output. We needed the print() function here because, unlike in the REPL, things aren’t automatically printed out when writing scripts.
Congratulations! You’ve written your first script. That’s kind of a big deal.
Rewrite your program so that you assign the message to a variable, then print the variable. This will make your program two lines instead of one. There’s a fancy programmer word for rewriting your code without changing it’s behavior—”refactoring.”
(optional) Are you already getting sick of typing python hello.py again and again? Try typing !! in the command line (the $). This will run your last line of code again.
(even more optional) If you’re on Windows and have a minute, try pressing the Windows button on your keyboard and searching for a program called IDLE that comes with Python. It’s a special editor (or IDE) that lets you run Python code from inside it. You might like it more than git bash.
Fundamentally, Python programs are just text files. You can write them in any text editor, like VS Code or Notepad on Windows. When you pass the text file to Python, it runs the code in the file one line at a time. There’s nothing special about .py files, they’re just regular text files. This makes them work well with command line tools like Git. The tools you’ve learned so far—the command line, Git, markdown, grep—are all designed to work well together, and the medium through which they all work is plain text.
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