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 Atom from https://atom.io/. This is where you’ll write your code.

Then, follow the Python 3 installation directions.

Regroup

You have Python 3 installed!
You may have seen the in-line REPL (we’ll revisit!).
You have a text editor — Atom — 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 = 4
y = 5
print(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.

Create a new file with a .py extension. Let’s call it my_file.py.
Open my_file.py in Atom.
In this file, declare some variables. Let’s mix integers and strings!

favorite_tv_show = "Ninja Warrior"
obstacles_cleared = 5
time = "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?