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Running Python on Your Computer

Lesson Objectives#

After this lesson, you will be able to…

  • Write Python 3 scripts locally.
  • Run Python 3 scripts via the command prompt.

Defining Assumptions#

We can't use repl.it forever! We can run Python right on our computers.

  • GA uses Macs for its default curriculum.
  • We are happy to help you program Python on Windows or Linux as well.
  • Sometimes you may need to ask questions about subtle differences!

Let's Get Installing#

This will take us 10 to 15 minutes, then we'll regroup.

First, install Visual Studio Code from https://code.visualstudio.com/download. This is where you'll write your code.

Then, follow the Python 3 installation directions by brew install python.

Regroup#

  • You have Python 3 installed!
  • You may have seen the in-line REPL (we'll revisit!).
  • You have a text editor — Visual Studio Code — installed.
  • You are ready to create a local .py file and run it.

In-Line REPL#

Let's check out a REPL.

  • Read-Evaluate-Print-Loop.
  • An interactive way to code.

Let's do it!

  • Open your terminal.
  • Then, open your in-line REPL:

Mac/Linux:

python

Windows:

py

We Do: Interactive Development#

You can type any Python code you want here. Let's declare a variable and do some math:

x = 4y = 5print(x + y)

Pro tip: exit() is the command for when you want to get out of this environment!

We Do: Local Files#

We can create a file with a .py extension — we can execute properly written Python code in a .py file.

  1. Create a new file with a .py extension. Let's call it my_file.py.
  2. Open my_file.py in Atom.
  3. In this file, declare some variables. Let's mix integers and strings!
favorite_tv_show = "Ninja Warrior"obstacles_cleared = 5time = "3 min, 20 sec"print("I cleared", obstacles_cleared, "on", favorite_tv_show, "in", time)

Save and close your file.

Pro tip: Make sure you have a print statement.

We Do: Running Local Files#

Now we have code in a file, but we need to run it.

  • Back on your terminal, we'll navigate to where that file is located:

    • cd stands for "change directory" ("directory" is another word for "folder").
    • cd my_folder changes to the directory my_directory.
    • cd .. goes up to the parent folder of the one you're in.

  • Running the file varies slightly between Windows and Mac/Linux:

    • Mac/Linux: python my_file.py
    • Windows: py my_file.py

Raise your hand if you need help!

Summary#

  • We now have Python 3 — the latest and greatest — installed.
  • We can use our in-line REPL in the terminal.
  • We can execute a local .py file with Python code in it.
  • We know how to do this regardless of whether we use Mac, Linux, or Windows.

Any questions?

Additional Resources#