The REPL: a Python Scratchpad

Scenario: You want to test one calculation without creating a project.

New words, in plain English

• REPL - Read-Evaluate-Print Loop: an interactive Python prompt
• Expression - code that produces a value
• Prompt - the >>> marker asking for input

At >>>, enter one expression at a time. Python reads it, evaluates it, prints the result, and loops. Leave with exit() or Ctrl-D.

Analogy: A Python program is like a clear set of instructions for a careful helper: names label things, indentation groups steps, and errors explain where the helper became confused.

A small, real example

>>> 6 * 7
42
>>> "shell".upper()
'SHELL'

Tip: Use the REPL for questions; use a file for work worth keeping.

Goal: Practice this idea in the py-variables-types challenge at /labs/python. Fix the broken program, run it yourself, then use check to prove the real end state.