1.5.2: IDLE Programming Environment: Notes on Python Interpreter, Interactive and Script Modes

Python Interpreter and Modes

• Python is an interpreted language. The Python interpreter can run programs saved in files or execute statements interactively typed at the keyboard.

• Python comes with IDLE, an integrated development environment (IDE) that simplifies writing, executing, and testing programs.

• When Python is installed, the Python interpreter is installed as well.

• The interpreter can operate in two modes: interactive mode and script mode.

  • Interactive mode: the interpreter waits for you to type Python statements on the keyboard, executes each statement, and then waits for another input.

  • Script mode: the interpreter reads a file that contains Python statements (a Python program or Python script) and executes each statement as it reads it.

Starting the interpreter in interactive mode

• After installation, start the interpreter from the operating system’s command line by typing: python.

• If you are on Windows, you can alternatively type Python in the Windows search box; you may see a program named something like Python 3.5 (the $3.5$ indicates the installed version). $3.5$ denotes the version referenced here as the latest at the time of writing.

• Clicking this item starts the Python interpreter in interactive mode (the Python shell).

• When the interpreter starts in interactive mode, you typically see a console display like: Python 3.x.y (an example given is Python 3.9.5).

• The prompt you see is the three chevrons >>>, which indicates the interpreter is waiting for you to type a Python statement.

• A simple first action is to print a message to the screen.

Interactive mode basics and examples

• Example: print a message on the screen

  • Code:

  • print('Python programming is fun!')

  • This prints: Python programming is fun! to the screen.

  • After executing, the interpreter shows the prompt again, waiting for another statement.

• You can try another example, e.g.:

  • print('That is the question?')

• If you type a statement incorrectly, the interpreter displays an error message. This immediate feedback makes interactive mode useful for learning.

• Quitting interactive mode:

  • Windows: press CTRL+Z and then Enter.

  • macOS/Linux: press CTRL+D.

• In Chapter 2 of the book, additional details about these statements are discussed.

Script mode: writing and running programs

• Interactive mode is great for testing, but the statements you enter there are not saved anywhere. To save a Python program, you must write statements to a file.

• Use a plain text editor (e.g., Notepad on Windows) to create a file containing Python statements.

• Save the file with a .py extension, which identifies it as a Python program. Example: test.py.

• To run the program, navigate to the directory where the file is saved and type on the command line:

  • python test.py

• This starts the Python interpreter in script mode and executes the statements in the file in order. When the program finishes, the interpreter exits.

Example program (three lines) saved as a file

• A Python program that displays three lines of text:

  • print('nudge, nudge')

  • print('wink, wink')

  • print('know what I mean?')

• Running this script with python test.py will print:

  • nudge, nudge

  • wink, wink

  • know what I mean?

Notes on editing and file types

• It is possible to use a word processor to create a Python program, but you must save the program as plain text; otherwise the Python interpreter cannot read its contents.

• Save files as plain text with the extension .py to identify them as Python programs (the example name: test.py).

• The phrase “the Python interpreter in script mode” refers to running a Python program from a file rather than typing commands interactively.

Quick reference and practical considerations

• Start interactive: from the OS command line, run python (on Windows you may see a listing like Python 3.5 in search results to start the interactive shell). The version shown may be represented as $3.5$ (latest at writing).

• Start script mode: save a file as name.py and run python name.py.

• Quit interactive mode: CTRL+Z (Windows) or CTRL+D (macOS/Linux).

• File extension: .py.

Context and broader relevance

• The interpreter works by reading and executing statements; interactive mode is ideal for experimentation and learning, while script mode enables running complete programs and sharing them as files.

• IDLE is a beginner-friendly environment that helps writing, executing, and testing Python programs.

• Appendix A (referenced in the material) provides installation instructions for Python on personal computers; in computer labs, Python is often pre-installed.

• The content also mentions the distinction between Python being an interpreted language and the practical workflow of writing and testing code before saving it as a script.

Mathematical and numerical notes (versions and references)

• Latest version at time of writing: $3.5$

• Example interactive shell display: Python 3.x.y (e.g., $3.9.5$)

Summary

• You can run Python in two modes: interactive and script.

• Interactive mode is great for quick experiments and learning; script mode is for saving and running complete programs.

• IDLE provides a friendly environment for beginners.

• To save and run programs, use a text editor to create a .py file and run it with python <filename.py>.

• The basic print example demonstrates how Python executes statements and provides immediate output in the interactive shell.