How to Run Python Scripts on Windows: From IDLE to Command Line

Anyone who has dabbled in Python knows there are several ways to run a script: an interactive REPL, a command‑line session, or an IDE, and the exact steps differ across operating systems. This article focuses on the basics for Windows users, using the built‑in interactive environment.

After a successful Python installation, you can enter the interactive REPL in two common ways. The first is to launch IDLE, which opens a dedicated window (see image). The second is to open the Start menu, run cmd, type python and press Enter to reach the >> prompt (see image).

At the >> prompt you type a statement and press Enter; Python evaluates it immediately and prints the result. The REPL works like a calculator, handling one statement at a time while retaining the last result in the special variable _, which you can reuse in subsequent expressions.

The variable _ stores the previous expression’s value. You can reference it to build new calculations. Remember to define any variables before using them; otherwise you’ll see a NameError, as illustrated by an undefined a variable, while length and width work because they were defined.

If you make a syntax mistake, Python aborts execution and displays an error message with the line number and description, helping you quickly locate and fix the bug.

Code entered in the interactive session is not persisted after you close the window. You can browse recent commands with the up/down arrow keys, but this history disappears once the session ends.

For longer programs, typing directly into the REPL becomes cumbersome. Instead, open a new file in IDLE via File → New Window (see image), write your script, and pay close attention to indentation to avoid IndentationError. Save the file with a .py extension, then run it by pressing F5 or selecting Run from the context menu; the output appears in the IDLE console.