Python Cheatsheet: Syntax, Collections, Files, and OOP

lessons = [
    {"title": "Variables", "complete": True},
    {"title": "Lists", "complete": False},
]

remaining = [lesson for lesson in lessons if not lesson["complete"]]
titles = {lesson["title"] for lesson in lessons}
by_title = {lesson["title"]: lesson for lesson in lessons}

def completion_percent(completed: int, total: int) -> int:
    """Return a whole-number completion percentage."""
    if total <= 0:
        return 0
    return round(completed / total * 100)

for index, lesson in enumerate(lessons, start=1):
    print(index, lesson["title"])

squares = (number * number for number in range(1_000_000))
first_ten = [next(squares) for _ in range(10)]

import json
from pathlib import Path


def load_config(path: Path) -> dict:
    try:
        with path.open(encoding="utf-8") as file:
            return json.load(file)
    except json.JSONDecodeError as error:
        raise ValueError(f"Invalid JSON in {path}") from error

from dataclasses import dataclass
from decimal import Decimal

@dataclass(frozen=True)
class Expense:
    category: str
    amount: Decimal


def test_expense_preserves_decimal_amount():
    expense = Expense("Food", Decimal("9.50"))
    assert expense.amount == Decimal("9.50")