Python Classes & OOP — Modeling Your World in Code

from dataclasses import dataclass, field
from datetime import datetime

@dataclass
class Task:
    title: str
    priority: int = 3
    done: bool = False
    created_at: datetime = field(default_factory=datetime.now)

    def complete(self) -> None:
        self.done = True

    def age_seconds(self) -> float:
        return (datetime.now() - self.created_at).total_seconds()

t = Task("Write essay", priority=1)
t.complete()
print(t)   # Task(title='Write essay', priority=1, done=True, ...)

@dataclass
class RecurringTask(Task):
    interval_days: int = 7

    def next_due(self) -> datetime:
        from datetime import timedelta
        return self.created_at + timedelta(days=self.interval_days)

r = RecurringTask("Water plants", interval_days=3)
print(r.next_due())
r.complete()   # inherited from Task

class TaskError(Exception):
    """Base class for task errors."""

class TaskAlreadyDoneError(TaskError):
    pass

@dataclass
class SafeTask(Task):
    def complete(self) -> None:
        if self.done:
            raise TaskAlreadyDoneError(f"{self.title!r} is already done")
        self.done = True

try:
    t = SafeTask("Study")
    t.complete()
    t.complete()   # second call raises
except TaskAlreadyDoneError as e:
    print(f"Caught: {e}")