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Introduction to Python

Python REPL

Interactive Python interpreter

Interview: Quick testing and debugging

Last Updated: June 12, 2026 • 6 min read

The Python REPL (Read-Eval-Print Loop) is an interactive interpreter that lets you execute Python statements one at a time and see results immediately. It's invaluable for quick testing, debugging, and exploration.

Starting the REPL

Type python3 (or python on Windows) in your terminal. You'll see the >>> prompt indicating the REPL is ready for input.

  • python3 — start the default REPL
  • python3 -i script.py — run a script then drop into REPL with all variables loaded
  • python3 -q — quiet mode (no version banner)
  • Type exit() or press Ctrl+D (Unix) / Ctrl+Z (Windows) to quit

REPL Features

  • The underscore variable (_): Holds the result of the last expression — useful for chaining calculations.
  • help(): Type help(object) to get interactive documentation for any object.
  • dir(): Lists all attributes and methods of an object — great for exploring unfamiliar modules.
  • Multi-line input: The REPL uses ... prompt for continuation lines (loops, functions, etc.).
  • History: Use arrow keys to navigate previous commands (requires readline support).

Enhanced REPLs

The standard REPL is basic. These alternatives provide a much richer experience:

  • IPython: Syntax highlighting, tab completion, magic commands (%timeit, %history). Install with pip install ipython.
  • bpython: Auto-suggestion, syntax highlighting, inline documentation.
  • ptpython: Modern REPL with syntax highlighting, multi-line editing, and mouse support.

Pro Tip

Use python3 -i script.py to run a script and then stay in the REPL with all variables loaded. This is incredibly useful for debugging — you can inspect any variable after the script runs.

Use Cases

Quick calculations and data exploration

Testing code snippets before adding to scripts

Debugging by inspecting objects interactively

Learning Python by experimenting with built-in functions

Common Mistakes

Not using IPython for a better interactive experience

Forgetting about the _ (underscore) variable for last result

Not knowing about python3 -i for post-script debugging

Pasting multi-line code with leading whitespace causing IndentationError