Two ways to run Python

The interactive shell

The first way is the REPLREPLRead, Evaluate, Print, Loop: Python waits for a line, runs it, shows the result, and waits again. Also called the interactive shell.. You start it by typing Python's name in the terminal with nothing after it.

py

python3

python3

The prompt changes to >>>. That's Python waiting for you. Type a line, press Enter, and it answers straight away:

>>> 3 + 4
7
>>> "Selam"
'Selam'
>>> print("Selam")
Selam

Notice that you didn't need print to see 7. The shell shows the value of whatever you type. It even shows text with its quotes, so you can tell text from numbers. When you're done, type exit() and press Enter to get back to the normal terminal.

The shell is perfect for quick questions: "what's 15% of 1,200?", "does this line work?". But nothing you type is saved. Close the window and it's gone.

Where am I: the terminal or Python?

The most common beginner mix-up is typing into the wrong place. Look at the start of the line you're typing on. The terminal's own prompt usually ends in >, $, or %, often after the folder you're in, like PS C:\Users\Hana> on Windows or hana@laptop ~ % on a Mac. Python's prompt is exactly three arrows, >>>, with nothing before them.

Terminal commands such as python3 --version or cd only work at the terminal prompt. Python code only works after >>>. If you get an error that makes no sense, check the prompt first.

Programs saved in files

The second way is a scriptscriptA program saved in a file ending in .py, run from top to bottom. Also called a Python file or a program file.: a file ending in .py that holds your whole program. Python runs it from the first line to the last and then stops. Almost everything you build in this course will be a script.

Scripts don't echo values the way the shell does. Only what you print appears. The code boxes on this site run your code as a script, so you can see this for yourself. Decide first: what does this print?

3 + 4
print(3 + 4)

7

Now run it, then add print(...) around the first line so both results appear.

3 + 4
print(3 + 4)

Running a file

Open your python-course folder in VS Code. In lesson 0.2 you saved setup_check.py there; if you didn't, create it now with a single line like print("Selam") and save it.

You can run it in two ways.

1. From the terminal

   In VS Code, choose Terminal, then New Terminal. It opens inside your folder. Type the command for your system:

   WindowsmacOSLinux

   Windows

   python setup_check.py

2. With the Run button

   With the file open, click the triangle Run Python File button at the top right of the editor. VS Code types a similar command into its terminal for you.

Either way, the terminal shows your three lines and returns to the prompt.

Which one to use

Use the shell to try one small thing and see the answer immediately. Use a script for anything you want to keep, run again, or build on. Most programmers keep both open: a script they're writing, and a shell for checking ideas.

A good rhythm while you learn: when you're unsure what a line does, try it in the shell (or in a code box here). Once it does what you want, copy it into your script. The code boxes on this site are a halfway point: you can edit and rerun them like a script, without saving anything.