So every caller uses the same validation boundary. Separate objects still have separate state, allowing two rooms to behave independently.

A class describes how an object is constructed and what operations it offers. init sets up one instance; self refers to that instance. Methods are functions operating on its state. A read-only property exposes availability without offering a public setter. The underscore is a Python convention, not a security boundary. Invalid requests raise; valid requests that cannot fit return False. This distinction is part of the public contract.

What the function promises: Room(capacity) accepts a nonnegative integer capacity. book(count) accepts a positive integer and returns whether the entire booking succeeds. No partial booking, cancellation, concurrency, or persistence is included.

class Room:
    def __init__(self, capacity):
        if type(capacity) is not int or capacity < 0:
            raise ValueError("Capacity must be a nonnegative integer")
        self._available = capacity

    @property
    def available(self):
        return self._available

    def book(self, count):
        if type(count) is not int or count <= 0:
            raise ValueError("Booking count must be a positive integer")
        if count > self._available:
            return False
        self._available -= count
        return True

a, b = Room(2), Room(2)
assert not a.book(3) and a.available == 2
assert a.book(1) and a.available == 1
assert b.available == 2
assert not Room(0).book(1)

Work and storage: Each operation is O(1) in the usual integer model. The design cost being controlled is duplicated validation, not algorithmic speed.

When to recognize it: Keep the data and the operations protecting its rules together.

Check before applying it: A class is not useful just because a noun exists. Start with an actual responsibility and a rule that must stay true.

No. Encapsulation organizes responsibility but does not synchronize execution. A lock or transactional storage boundary must protect check-and-update if concurrent callers are allowed.