b_plugged.py

# b_plugged.py
from copy import copy
from a_encapsulation import Bob, Leaky, check_for_leaks

class Plugged(Leaky):  # Only to reduce code here
    def __init__(self, n: int, lst: list):
        super().__init__(n, lst)

    @property
    def x(self) -> int:
        return self._n

    @property  # Decouple by copying:
    def lst(self) -> list:
        return self._lst.copy()

    @property  # Ditto:
    def bob(self) -> Bob:
        return copy(self._bob)

    # Can re-leak here & in subclasses:
    def leak(self) -> Bob:
        return self._bob

def test_leaks():
    before, after = check_for_leaks(Plugged)
    assert (
        before
        == """
Plugged:
    n: 42
    lst: ['x', 'y']
    bob: Bob
"""
    )
    assert (
        after
        == """
Plugged:
    n: 42
    lst: ['x', 'y']
    bob: Bob
"""
    )