PCPP1 Advanced Object Oriented Programming Practice Test 2 — 15 Questions

Question 1

How do you correctly call a method from a sibling class in a diamond inheritance structure using super()?

Accepted Answer

Use super() in each class to delegate to the next class in the MRO.. super() follows the Method Resolution Order (MRO), which correctly handles diamond inheritance by delegating calls to the next class in the chain, not just the parent.

Answer

Call the grandparent class directly.

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Use the __bases__ attribute to iterate through parents.

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Explicitly call the sibling class method by name.

Question 2

Which magic method is responsible for providing the informal string representation of an object, typically used for user-facing output?

Accepted Answer

__str__. The __str__ method is used for informal, readable string representations, whereas __repr__ is for formal, unambiguous representations.

Answer

__format__

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__unicode__

Answer

__repr__

Question 3

What is the result of applying the @staticmethod decorator to a method inside a class that also defines a metaclass?

Accepted Answer

The method is correctly bound as a static function regardless of the metaclass.. The @staticmethod decorator creates a static method object which is stored in the class dictionary; it is independent of the metaclass's __init__ logic for instance methods.

Answer

The metaclass must manually convert it back to a static method.

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It raises a TypeError at class definition time.

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The metaclass will treat the method as an instance method.

Question 4

You are implementing the Observer pattern. Why should you avoid using a strong reference to the observers in the subject's list?

Accepted Answer

It prevents the observer from being garbage collected when it is no longer needed.. Strong references prevent garbage collection of the observers, leading to memory leaks if observers are meant to be temporary.

Answer

It causes circular dependency issues.

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It makes the notify method thread-unsafe.

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It violates the principle of encapsulation.

Question 5

When using abstract base classes (ABCs) from the abc module, what happens if a class inherits from an ABC but fails to implement one of the abstract methods?

Accepted Answer

The class will be marked as abstract and will raise a TypeError upon instantiation.. Python will raise a TypeError when you attempt to instantiate the class, preventing the creation of an incomplete object.

Answer

The class will be created, but calling the missing method will raise an AttributeError.

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The missing method will default to a 'pass' statement.

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The parent ABC will automatically provide a NotImplementedError.

Question 6

Which magic method should you implement to make your objects support the 'with' statement context manager?

Accepted Answer

__enter__ and __exit__. The __enter__ and __exit__ methods are required to implement the context manager protocol.

Answer

__context__

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__open__ and __close__

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__init__ and __del__

Question 7

Which of the following describes the purpose of the __slots__ attribute in a class?

Accepted Answer

To improve performance and reduce memory usage.. __slots__ restricts the creation of new instance attributes and reduces memory footprint by preventing the creation of a per-instance __dict__.

Answer

To allow private attribute access.

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To define the method resolution order.

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To prevent inheritance.

Question 8

In the context of the Factory pattern in Python, what is a typical benefit of using a registry-based approach instead of a large if-else block?

Accepted Answer

It enables easy extension by adding new products without changing the factory.. A registry-based factory stores a mapping (typically a dict) from product identifiers to their concrete classes or creator callables, so the factory simply looks up and instantiates the requested product. Adding a new product means registering it in the mapping — no modification to the factory's control flow is required, satisfying the Open/Closed Principle. This decouples the factory from concrete product classes and makes extension a configuration concern rather than a code change.

Answer

It guarantees thread safety without locks.

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It prevents the instantiation of abstract classes.

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It significantly reduces memory usage.

Question 9

When overriding the __getattr__ method, what must you be careful to avoid?

Accepted Answer

Infinite recursion by accessing non-existent attributes.. Infinite recursion occurs if you try to access an attribute inside __getattr__ that does not exist, triggering __getattr__ again.

Answer

Raising AttributeError.

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Accessing class attributes.

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Calling super().__getattr__.

Question 10

Which magic method allows an object to behave like a function?

Accepted Answer

__call__. The __call__ method enables an object to be invoked with parentheses syntax.

Answer

__apply__

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__invoke__

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__func__

Question 11

What is the effect of setting __slots__ in a parent class on a child class that does not define its own __slots__?

Accepted Answer

The child class will have a __dict__ attribute, overriding the parent's optimization.. The child class will receive an instance __dict__ unless it also defines __slots__, effectively defeating the memory optimization of the parent.

Answer

The child class will raise an error at instantiation.

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The child class will inherit the memory savings automatically.

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The child class will be unable to add new attributes.

Question 12

If you define a class with a metaclass that has a custom __call__ method, when is that __call__ method executed?

Accepted Answer

When an instance of the class is created.. The metaclass's __call__ method is invoked whenever the class created by that metaclass is instantiated (i.e., when you call the class name like MyClass()).

Answer

Every time an instance method is called.

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When the metaclass is first imported.

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When the class itself is defined.

Question 13

When implementing the Singleton pattern, what is the advantage of using a module-level instance over a class-based Singleton?

Accepted Answer

It is simpler and leverages Python's built-in module caching mechanism.. Python modules are naturally Singletons because they are initialized only once upon the first import.

Answer

It is more secure.

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It allows multiple instances if needed.

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It supports lazy loading.

Question 14

Which magic method is used to control how an instance is displayed when using the print() function?

Accepted Answer

__str__. print() implicitly calls str(obj), which in turn calls __str__.

Answer

__display__

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__repr__

Answer

__print__

Question 15

Why might you use the __init_subclass__ hook instead of a metaclass?

Accepted Answer

It is easier to implement and avoids metaclass conflicts.. __init_subclass__ provides a simpler way to perform logic when a subclass is created, without the complexity and inheritance issues associated with custom metaclasses.

Answer

Metaclasses are deprecated.

Answer

Metaclasses cannot be used for registration.

Answer

It is faster at runtime.