PCPP1 Advanced Object Oriented Programming Practice Test 3 — 15 Questions

Question 1

When designing a class hierarchy, what is the best way to prevent a method from being overridden by subclasses?

Accepted Answer

Using the @final decorator from typing.. The @final decorator from the typing module (PEP 591) is the standard, type-checker-enforced way to mark a method as non-overridable in Python. When applied to a method, static type checkers like mypy or Pyright will flag any subclass that attempts to override it, and applying @final to a class prevents subclassing entirely. Python itself does not enforce this at runtime, but the decorator is the idiomatic, documented mechanism for expressing the intent.

Answer

Defining it as a private method.

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Defining it as a static method.

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Using the 'final' keyword.

Question 2

In the context of the Observer pattern, what is the benefit of an event-driven system over a direct-method-call approach?

Accepted Answer

Decoupling between the subject and observers.. Decoupling is the primary benefit; the subject does not need to know the implementation details of the observers.

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Reduced memory usage.

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Increased performance.

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Automatic thread synchronization.

Question 3

What is the primary difference between @classmethod and @staticmethod?

Accepted Answer

@classmethod receives the class as the first argument; @staticmethod does not.. @classmethod receives the class as the first argument, while @staticmethod receives no implicit class or instance argument.

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@staticmethod can access instance variables.

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@classmethod is for private methods.

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@classmethod is slower.

Question 4

Why does the 'abc' module provide the 'ABCMeta' metaclass?

Accepted Answer

To enforce abstract method implementation at instantiation.. ABCMeta is the metaclass that implements the logic to prevent instantiation of classes with abstract methods.

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To allow private methods.

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To improve method resolution speed.

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To support multiple inheritance.

Question 5

In the Factory pattern, what should you do if the requested type is unknown?

Accepted Answer

Raise a ValueError.. Raising a ValueError or a custom 'UnknownTypeException' is the standard way to handle invalid inputs in a factory.

Answer

Log the error and return the base class.

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Return a default instance.

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Return None.

Question 6

What is the purpose of the 'weakref' module in relation to the Observer pattern?

Accepted Answer

To prevent memory leaks.. It allows the subject to maintain references to observers without preventing their collection by the garbage collector.

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To allow private access to observers.

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To ensure thread safety.

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To serialize observers.

Question 7

Which method is used to customize the behavior of the 'in' operator?

Accepted Answer

__contains__. The __contains__ method is called when using the 'in' or 'not in' operators.

Answer

__has__

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__find__

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__in__

Question 8

How do you define a property in a class to make it read-only?

Accepted Answer

Define a property with only @property, no @setter.. By defining the property with only a getter (using @property) and omitting the setter method.

Answer

Use the 'readonly' decorator.

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Use the 'final' modifier.

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Set the attribute to private.

Question 9

What does the @abstractmethod decorator do when applied to a method inside an ABC?

Accepted Answer

It requires the subclass to implement the method.. It marks the method as requiring an override in any non-abstract concrete subclass.

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It prevents the method from being called.

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It automatically generates a default implementation.

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It makes the method faster.

Question 10

What is the consequence of not calling super().__init__() in a class with multiple inheritance?

Accepted Answer

The initialization chain for parent classes is interrupted.. The MRO chain will break, and sibling classes may not be initialized properly, potentially causing missing attributes or logic errors.

Answer

The class will not be created.

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All attributes will be lost.

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Python will raise a RuntimeError.

Question 11

Which magic method enables index access (e.g., obj[i])?

Accepted Answer

__getitem__. The __getitem__ method allows an object to support indexing.

Answer

__index__

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__setitem__

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__access__

Question 12

How do you implement the 'Strategy' pattern in Python?

Accepted Answer

By passing strategy instances into the context constructor.. By injecting different strategy objects into a context class, which then delegates operations to the injected object.

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By using a large switch-case statement.

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By creating a metaclass for all strategies.

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By using inheritance for every strategy.

Question 13

What is the difference between a class-level variable and an instance-level variable?

Accepted Answer

Class-level variables are shared by all instances.. A class-level variable is shared across all instances of the class, whereas an instance-level variable is specific to each object.

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Instance-level variables cannot be modified.

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Class-level variables are always constant.

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Class-level variables are hidden from subclasses.

Question 14

What is the purpose of the 'type' function when called with three arguments?

Accepted Answer

To create a new class dynamically.. It is used for dynamic class creation: type(name, bases, dict).

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To register a class.

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To inherit from multiple classes.

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To check object type.

Question 15

Which magic method is triggered when an object is deleted using the 'del' keyword?

Accepted Answer

__del__. The __del__ method is called when the object's reference count reaches zero.

Answer

__clear__

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__remove__

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__destroy__