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Chapter 12 - Designing and Deploying Command Line Programs (Python)

Here's a concise walkthrough of the main ideas in Chapter 12, each with a small example.

Designing and Deploying Command Line Programs (intro)​

Goal: move from running code in Mu to running scripts as real commands from the terminal, using virtual environments, pip, and deployment techniques.

A Program by Any Other Name​

Defines terms: program, script, command, shell script/batch file, application, app, web app, and how they differ.

Example shell script:

#!/usr/bin/env bash
echo "Starting backup..."
python backup_to_zip.py
echo "Done."

Using the Terminal​

Explains what CLI/terminal/shell/console are and how to open them on each OS, plus how prompts look and how to run Python or a .py file from the terminal.

Example (Windows):

C:\Users\al> python C:\Users\al\Scripts\yourScript.py

Example (Linux/macOS):

python3 yourScript.py

The cd, pwd, dir, and ls Commands​

  • cd changes current directory.
  • pwd (macOS/Linux) prints working directory.
  • cd with no args on Windows shows current dir.
  • dir (Windows) and ls (macOS/Linux) list contents.

Example (Windows):

C:\Users\al> cd Desktop
C:\Users\al\Desktop> cd ..
C:\Users\al>

Example listing:

ls
# or
dir

The PATH Environment Variable​

PATH is a "search list" of folders the shell looks in to find commands like python or ls.

  • Windows: checks CWD first, then folders in PATH.
  • macOS/Linux: only PATH; use ./program for CWD.

Example:

echo $PATH
# /home/al/.local/bin:/usr/local/bin:/usr/bin:...

PATH Editing​

Recommends a Scripts folder under your home and adding it to PATH so you can run your scripts from anywhere.

  • Windows: edit user "Path" via "Edit environment variables for your account", add C:\Users\al\Scripts.
  • macOS: add export PATH=/Users/al/Scripts:$PATH to ~/.zshrc.
  • Linux: add export PATH=/home/al/Scripts:$PATH to ~/.bashrc.

The which and where Commands​

  • which name (macOS/Linux)
  • where name (Windows)

Show where a command actually lives in PATH.

Example:

which python3
# /Library/Frameworks/.../python3

where python
# C:\Users\al\AppData\Local\Programs\Python\Python313\python.exe

Virtual Environments​

Motivation: different projects may need conflicting versions of the same package; system Python on macOS/Linux is used by the OS, so avoid polluting it. Use venv to create isolated environments.

Creating a Virtual Environment​

In Scripts folder:

# Windows
cd C:\Users\al\Scripts
python -m venv .venv

# macOS/Linux
cd ~/Scripts
python3 -m venv .venv

Creates a .venv folder containing its own Python and pip.

Activating a Virtual Environment​

Windows:

C:\Users\al\Scripts> cd .venv\Scripts
C:\Users\al\Scripts\.venv\Scripts> activate.bat
(.venv) C:\Users\al\Scripts\.venv\Scripts> where python.exe
# first entry is ...\.venv\Scripts\python.exe

macOS/Linux:

cd ~/Scripts/.venv/bin
source activate
(.venv) ...$ which python3
# ~/Scripts/.venv/bin/python3

python -m pip list inside venv shows only minimal packages.

Notes:

  • Use one venv per project ideally; for small scripts, one shared venv in Scripts is OK.
  • On macOS/Linux, avoid installing third-party packages into system Python; use venv instead.
  • Mu has its own venv; packages in Scripts/.venv aren't visible to Mu's F5 runs.

Deactivate: deactivate.bat (Windows) or deactivate (macOS/Linux) or close the terminal; delete .venv folder to remove the environment.

Installing Python Packages with pip​

Use python -m pip / python3 -m pip rather than bare pip to ensure you hit the right Python.

Installing, Listing, Upgrading, Uninstalling​

Install:

python -m pip install package_name

List:

python -m pip list

Upgrade:

python -m pip install -U package_name

Install specific version:

python -m pip install package_name==1.17.4

Uninstall:

python -m pip uninstall package_name

Warning: if using Anaconda, use conda instead of pip inside conda envs.

Installing the automateboringstuff3 Package​

Meta-package that pins all book-used packages and their versions.

# Windows
python -m pip install automateboringstuff3

# macOS/Linux
python3 -m pip install automateboringstuff3

Self-Aware Python Programs​

Shows built-ins and modules that let your script know about itself and environment.

Key pieces:

  • __file__ – path to the current .py file as a string (not in the interactive shell).
  • Path(__file__) – handy for locating resources next to your script.
  • sys.executable – path to the Python executable.
  • sys.version / sys.version_info – version info.
  • os.name – 'nt' (Windows) or 'posix' (macOS/Linux).
  • sys.platform – 'win32', 'darwin', 'linux'.
  • platform module – more detailed OS/CPU info.

Example:

from pathlib import Path
import sys, os, platform

print(Path(__file__))         # script path
print(sys.executable)         # interpreter path
print(sys.version_info.major) # e.g. 3
print(os.name, sys.platform)  # 'nt' 'win32' or 'posix' 'darwin'
print(platform.system())      # 'Windows'/'Darwin'/'Linux'

Checking whether a module is installed:

import sys

try:
    import nonexistentModule
except ModuleNotFoundError:
    print('nonexistentModule is required. Please install it.')
    sys.exit(1)

Text-Based Program Design​

Motivates "TUI" programs and introduces several design patterns for CLIs.

Short Command Names​

Advocates short, type-friendly command names (cp vs copy) for commands you'll run often; use which/where and web search to ensure you don't collide with existing commands.

Example: choose ccwd for "copy current working directory" instead of a long name.

Command Line Arguments​

Explains sys.argv and how to design simple argument sets; suggests argparse for more complex scenarios.

Example:

python yourScript.py spam eggs

Inside yourScript.py:

import sys
print(sys.argv)
# ['yourScript.py', 'spam', 'eggs']

With spaces in one argument:

python yourScript.py "hello world"
# sys.argv == ['yourScript.py', 'hello world']

Clipboard I/O​

Pattern: pyperclip.paste() → process → pyperclip.copy(), so your script acts like a filter over the clipboard.

General steps:

  1. import pyperclip
  2. text = pyperclip.paste()
  3. transform text
  4. pyperclip.copy(result)

Example mini-tool:

import pyperclip

text = pyperclip.paste()
result = text.strip().upper()
pyperclip.copy(result)
print('Transformed text copied to clipboard.')

Colorful Text with Bext​

Introduces bext for colored text and simple TUI features; only works from real terminals, not Mu.

Install:

python -m pip install bext

Basic colors:

import bext

bext.fg('red')
print('This text is red.')
bext.bg('blue')
print('Red text on blue background.')
bext.fg('reset')
bext.bg('reset')

Other helpers:

  • bext.clear() – clear screen.
  • bext.width(), bext.height() – terminal size.
  • bext.hide(), bext.show() – cursor.
  • bext.title(text) – window title.
  • bext.goto(x, y) – move cursor.
  • bext.get_key() – wait for and return key name.

Key reading example:

import bext

print('Press a key...')
key = bext.get_key()
print('You pressed:', key)

Terminal Clearing​

Gives bext.clear() and also a pure-Python one-liner using os.system and a conditional expression.

Custom clear():

import os

def clear():
    os.system('cls' if os.name == 'nt' else 'clear')

Sound and Text Notification​

Discusses using sound sparingly as a notification tool; introduces playsound3 for simple audio playback.

Install:

python -m pip install playsound3

Example:

import playsound3

playsound3.playsound('hello.mp3')

Notes:

  • playsound() blocks until audio finishes; long files pause your program.
  • If filenames with odd characters cause exceptions, pass a Path object instead of a plain string.

Also notes: text output should remain pipe-friendly (e.g. usable in Unix pipelines), so noisy, verbose output can reduce composability; keep CLIs focused and predictable.

Overall idea of the chapter​

Chapter 12 covers everything needed to turn Python scripts into real command-line tools: terminal navigation, PATH setup, virtual environments for isolation, pip for package management, self-awareness (__file__, sys, platform), and TUI design patterns (arguments, clipboard I/O, colored text, sound notifications).