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}")