Running Python Programs in Windows Interactive Shell: A Step‑by‑Step Guide

After installing Python, you can run scripts in several ways; this article focuses on using the interactive environment on Windows.

Method 1: Open the IDLE that comes with Python and use its interactive window (see screenshot). The prompt >>> appears, ready for input.

Method 2: Open the Start menu, type cmd, press Enter, then type python and hit Enter to start the interactive shell (see screenshot).

At the >>> prompt, type a statement and press Enter to see the result. The environment works like a calculator, evaluating one line at a time. The special variable _ holds the result of the previous expression, which can be reused in subsequent calculations. An example shows that referencing an undefined variable (e.g., a) raises a NameError, while defined variables ( length, width) work correctly.

If a syntax error occurs, Python prints a traceback with the line number and error message, making it easy to locate and fix the problem.

Pressing the up/down arrow keys cycles through recent commands, but the history is not persisted after the session ends.

For longer programs, the interactive shell becomes inconvenient. In IDLE, choose File → New Window to open an editor, write your code (pay careful attention to indentation to avoid IndentationError ), save the file with a .py extension (Ctrl+S), and run it with F5 or by right‑clicking and selecting Run . The output then appears in the IDLE shell.