Python for Mac

1. Getting Started on Mac

macOS includes Python 3.9 for system use. Never use it. Install Python 3.14 yourself.

Open Terminal

Press ⌘ Space → type "Terminal" → Enter. For a better experience, install iTerm2.

Install Python Properly

# Check system Python (ignore this)
python3 --version
# => Python 3.9.6

# Option A: Homebrew (recommended)
brew install python
python3 --version
# => Python 3.14.0

# Option B: python.org Universal2 installer
# Downloads to /Library/Frameworks/Python.framework

Create Your First Project

mkdir ~/Projects/hello-mac && cd $_
python3 -m venv .venv
source .venv/bin/activate   # (zsh/fish/bash)

# Now 'python' points to 3.14 inside the venv
python -m pip install --upgrade pip
python --version

deactivate  # exit venv

VS Code Setup (2026)

1. Install VS Code → Extensions: "Python" (Microsoft) + "Pylance"
2. Open your project folder
3. ⌘⇧P → "Python: Select Interpreter" → pick ./.venv/bin/python
4. New integrated terminal auto-activates venv

2. Core Syntax Rules

Indentation is law

Use 4 spaces. No tabs, no braces.

def can_vote(age):
    if age >= 18:
        return True
    else:
        return False  # aligned with 'if'

Comments & Docstrings

# Single line comment

def fetch():
    """Triple-quoted docstring - describes the function."""
    pass

Variables & Naming

• snake_case for variables/functions
• PascalCase for classes
• UPPER_SNAKE for constants
• Case-sensitive: name ≠ Name

Dynamic Typing

x = 10      # int
x = "now a string"  # same name, new type - allowed

Print and Input

print("Hello Mac")
name = input("Your name? ")  # always returns str

F-strings (3.6+) & T-strings (3.14 NEW)

name = "Ada"
year = 2026
print(f"{name} runs Python {year}")
print(f"{year = }")  # debug: year = 2026

# Python 3.14 Template Strings - for safe queries
user_id = 42
query = t"SELECT * FROM users WHERE id = {user_id}"
# Unlike f-strings, 'query' is a Template object.
# Database drivers can handle it safely, preventing SQL injection.
# Use for HTML, SQL, shell commands.

3. Data Types

# Type checking
type([1,2])        # <class 'list'>
isinstance(x, str) # True/False

4. Operators

5. Control Flow

# if / elif / else
score = 85
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
else:
    grade = "C"

# for loop
for app in ["Safari", "Terminal", "VS Code"]:
    print(app)

# while with else
n = 3
while n > 0:
    print(n)
    n -= 1
else:
    print("liftoff")

# break / continue
for i in range(10):
    if i == 5: continue
    if i == 8: break

match-case (Python 3.10+)

match status_code:
    case 200 | 201:
        print("OK")
    case 404:
        print("Not found")
    case 500 | 502 | 503:
        print("Server error")
    case _:
        print("Unknown")

Comprehensions

squares = [x*x for x in range(5)]              # [0,1,4,9,16]
evens = {x for x in range(10) if x % 2 == 0}   # set
mapping = {x: chr(65+x) for x in range(3)}     # {0:'A',1:'B',2:'C'}

6. Functions & Arguments — The Full Picture

def func_name(parameters) -> return_type:
    """Docstring"""
    return value

Positional & Keyword

def add(a, b):
    return a + b

add(2, 3)        # positional
add(b=3, a=2)    # keyword

Default Values

def greet(name, greeting="Hello"):
    return f"{greeting}, {name}"

*args — Variable Positional

def total(*numbers):
    return sum(numbers)

total(1, 2, 3, 4)  # 10

**kwargs — Variable Keyword

def config(**options):
    print(options)

config(theme="dark", debug=True)
# {'theme': 'dark', 'debug': True}

Keyword-Only Arguments (after *)

def connect(host, *, port=443, timeout=10):
    ...

connect("apple.com", port=8443)  # OK
# connect("apple.com", 8443)    # TypeError

Positional-Only (before /) Python 3.8+

def divide(a, b, /, c):
    return a / b + c

divide(10, 2, c=5)  # a,b must be positional

Complete Signature

def ultimate(pos1, pos2, /, standard, *args, kw_only, **kwargs):
    """Order matters:
    1. positional-only
    2. standard
    3. *args
    4. keyword-only
    5. **kwargs
    """

Type Hints & Lambdas

def parse(s: str) -> int | None:
    return int(s) if s.isdigit() else None

square = lambda x: x * x
# same as def square(x): return x*x

7. Modules & Packages

# Standard library
import os
import sys
from pathlib import Path
from datetime import datetime as dt

# Third-party (after pip install)
import requests

# Never do this:
# from module import *

Installing Packages

# Inside activated venv
pip3 install requests httpx rich

# Pin versions
pip freeze > requirements.txt

# Reinstall elsewhere
pip install -r requirements.txt

8. Virtual Environments on Mac

Isolates dependencies per project. macOS Terminal uses zsh by default.

python3 -m venv .venv
source .venv/bin/activate
which python   # .../Projects/.../.venv/bin/python

# VS Code detects .venv automatically
# To leave:
deactivate

Add to .zshrc for convenience:

alias venv='python3 -m venv .venv && source .venv/bin/activate'

9. Object-Oriented Python

class MacApp:
    platform = "macOS"  # class attribute
    
    def __init__(self, name: str, version: float):
        self.name = name        # instance attribute
        self.version = version
    
    def launch(self):
        return f"Launching {self.name} {self.version}"
    
    @property
    def bundle_id(self):
        return f"com.example.{self.name.lower()}"

# Inheritance
class ProApp(MacApp):
    def __init__(self, name, version, pro_features):
        super().__init__(name, version)
        self.pro_features = pro_features

Dataclasses (less boilerplate)

from dataclasses import dataclass

@dataclass
class Window:
    title: str
    width: int = 800
    height: int = 600
    visible: bool = True

win = Window("Finder")

10. Error Handling

try:
    data = Path("config.json").read_text()
    config = json.loads(data)
except FileNotFoundError:
    print("Config missing - using defaults")
    config = {}
except json.JSONDecodeError as e:
    print(f"Invalid JSON: {e}")
    raise  # re-raise
else:
    print("Config loaded successfully")
finally:
    print("Cleanup complete")

Raise your own:

if age < 0:
    raise ValueError("age cannot be negative")

11. Files & Paths — The Mac Way

Use pathlib, not string concatenation. macOS paths use /.

from pathlib import Path

home = Path.home()  # /Users/you
docs = home / "Documents"
project = docs / "Python" / "demo.txt"

# Create directory
project.parent.mkdir(parents=True, exist_ok=True)

# Write
project.write_text("Hello from Mac\n", encoding="utf-8")

# Read safely with context manager
with open(project, "r", encoding="utf-8") as f:
    for line in f:
        print(line.strip())

# Common operations
list(docs.glob("*.pdf"))      # find PDFs
project.exists()
project.unlink()  # delete

12. Command-Line Arguments

Basic: sys.argv

import sys

# python3 script.py input.txt -v
print(sys.argv)
# ['script.py', 'input.txt', '-v']

filename = sys.argv[1] if len(sys.argv) > 1 else "default.txt"

Professional: argparse

import argparse

parser = argparse.ArgumentParser(
    prog="imgtool",
    description="Resize images on macOS"
)
parser.add_argument("input", help="Input image path")
parser.add_argument("-o", "--output", default="out.jpg")
parser.add_argument("-w", "--width", type=int, default=800)
parser.add_argument("-v", "--verbose", action="store_true")

args = parser.parse_args()
print(f"Resizing {args.input} to {args.width}px")
if args.verbose:
    print("Verbose mode on")

Run: python3 imgtool.py photo.png -w 1200 -v

13. Standard Library Highlights

14. Mac Workflow Tips

# Example executable script ~/bin/backup
#!/usr/bin/env python3
from pathlib import Path
import shutil
src = Path.home() / "Documents"
dst = Path("/Volumes/Backup")
shutil.copytree(src, dst / "Documents", dirs_exist_ok=True)
print("Backup complete")

15. Quick Reference Table

16. Next Steps Checklist

• Install Python 3.14 via Homebrew and create a test venv
• Configure VS Code to use your venv interpreter
• Write a CLI tool using argparse with positional and keyword-only args
• Practice pathlib: list all Downloads > 10MB
• Build a small class with dataclass and type hints
• Convert an f-string SQL query to a safe t-string
• Set up Ruff formatting on save in VS Code
• Publish your first package to TestPyPI using uv build