Challenge 3: A Custom Exception for a Missing Task — Possible Solution
====================================================================

from tasks.models import Task

class TaskNotFoundError(Exception):
    pass

class TaskStorage:
    # ... __init__, load, save unchanged from the chapter ...

    def find(self, tasks: list[Task], task_id: int) -> Task:
        for task in tasks:
            if task.id == task_id:
                return task
        raise TaskNotFoundError(f"No task found with id {task_id}")

# usage example:
storage = TaskStorage(...)
tasks = storage.load()

try:
    task = storage.find(tasks, 99)
except TaskNotFoundError as e:
    print(f"Error: {e}")

Output (assuming no task with id 99 exists):
Error: No task found with id 99

WHY THIS WORKS AS AN ANSWER
------------------------------
class TaskNotFoundError(Exception): pass reuses the exact custom-
exception pattern from Course 2, Chapter 3's own InsufficientFundsError
example — a class inheriting from Exception, with pass as the entire
body being enough to make it a real, distinct, catchable type.

find(self, tasks: list[Task], task_id: int) -> Task: reuses this
course's own Chapter 5 type-hint conventions directly — list[Task] and
task_id: int as parameter hints, -> Task as the return type,
documenting that this method either returns a real Task or doesn't
return at all (it raises instead).

The for loop with if task.id == task_id: return task reuses ordinary
list iteration and comparison to search for a matching task, returning
immediately the moment a match is found — the same "search, return
early on match" shape as many earlier challenges in this course.

raise TaskNotFoundError(f"No task found with id {task_id}") only runs
if the loop completes without ever finding a match — reusing the
f-string-with-descriptive-message pattern from Course 2, Chapter 3's
own custom exception example, so the error message identifies exactly
which id was missing rather than a generic failure.

try/except TaskNotFoundError as e: at the call site reuses Course 2,
Chapter 3's exception-catching mechanics precisely, catching this
specific custom type by name rather than a generic Exception — making
the calling code's intent (specifically handling a missing-task case)
immediately clear from the except clause itself.