PCAP Object-Oriented Programming Practice Test 5 — 15 Questions

Question 1

Refer to the exhibit. What is the output?

Accepted Answer

5. Option A is correct because the code defines a class `A` with a class attribute `x = 5`. The `__init__` method sets an instance attribute `self.x = 0`, but the `print` statement accesses `A.x`, which refers to the class attribute, not the instance attribute. Therefore, the output is `5`.

Answer

0

Answer

-3

Answer

AttributeError

Question 2

A developer wants to ensure that a class attribute is shared across all instances. Which approach should be used?

Accepted Answer

Define the attribute in the class body, outside any methods.. Option C is correct because defining an attribute in the class body, outside any methods, creates a class attribute that is shared across all instances. Class attributes are stored in the class's __dict__ and are accessible via the class or any instance, unless shadowed by an instance attribute.

Answer

Use the @property decorator.

Answer

Define the attribute inside a method without using self.

Answer

Define the attribute inside __init__ using self.

Question 3

A programmer writes a class with a method that should be called on the class itself, not on instances. Which decorator is appropriate?

Accepted Answer

@classmethod. The @classmethod decorator transforms a method so that it receives the class itself as the first implicit argument (cls), rather than an instance (self). This allows the method to be called on the class directly, e.g., MyClass.my_method(), and is the correct choice when a method should operate on the class level, not on instances.

Answer

@property

Answer

@abstractmethod

Answer

@staticmethod

Question 4

A team is using inheritance but wants to prevent a method from being overridden in subclasses. What Python feature can enforce this?

Accepted Answer

Use a private method with double underscore prefix (__method).. Option A is correct because in Python, prefixing a method name with double underscores (e.g., `__method`) triggers name mangling, which renames the method to `_ClassName__method` at compile time. This prevents subclasses from accidentally overriding the method, as the mangled name is unique to the class where it is defined, effectively making it private and non-overridable in subclasses.

Answer

Use a @final decorator.

Answer

Use @staticmethod.

Answer

Use @abstractmethod.

Question 5

A class inherits from two parent classes that both have a method with the same name. When calling the method on the child, only one parent's version is executed. What Python mechanism determines which one?

Accepted Answer

Method Resolution Order (MRO).. Python uses the C3 linearization algorithm to compute the Method Resolution Order (MRO) for a class. When a method is called on an instance, Python searches the MRO from left to right and executes the first implementation it finds. This ensures a consistent and predictable order of inheritance, even in diamond or multiple-inheritance scenarios.

Answer

Method overloading by signature.

Answer

Explicit super() call in the child class.

Answer

Inheritance depth (closest parent wins).

Question 6

You are designing a class that should behave like a sequence and support slicing. Which special methods must be implemented?

Accepted Answer

__getitem__ and __len__. For a class to support slicing in Python, it must implement both `__getitem__` (to handle indexing and slice objects) and `__len__` (to define the sequence length, which is required for proper slice boundary handling). Together, these satisfy the sequence protocol, enabling Python's slicing syntax like `obj[start:stop:step]`.

Answer

__len__ and __contains__

Answer

__iter__ and __next__

Answer

__getitem__ alone

Answer

__getitem__ and __setitem__

Question 7

A class has an attribute that should be computed on access and cached for subsequent accesses. Which pattern is most appropriate?

Accepted Answer

Use a custom descriptor that caches the value in the instance's __dict__.. Option B is correct because a custom descriptor with a __get__ method can compute the attribute value on first access and store it in the instance's __dict__ for subsequent accesses. This pattern, often called a cached property, ensures the computation happens only once per instance, which is exactly what the question requires.

Answer

Use __slots__ to define the attribute.

Answer

Use a @classmethod to compute the value.

Answer

Use a @staticmethod to compute the value.

Question 8

A programmer wants to create a class that cannot be instantiated directly, only through a factory method. Which approach should be used?

Accepted Answer

Override __new__ to raise an exception unless called from a classmethod factory.. Option C is correct because overriding `__new__` allows the programmer to control instance creation at the lowest level. By checking the call stack or a flag set by a classmethod factory, `__new__` can raise an exception when instantiation is attempted directly, while still allowing the factory method to create instances. This ensures the class cannot be instantiated directly, only through the designated factory.

Answer

Raise an exception in __init__ if called directly.

Answer

Define the class as abstract using ABC and @abstractmethod.

Answer

Use a metaclass to prevent instantiation.

Question 9

When a class defines both __getattr__ and __getattribute__, which one is called when accessing an attribute that exists in the instance?

Accepted Answer

__getattribute__ is called, and __getattr__ is not called.. In Python, when both __getattr__ and __getattribute__ are defined in a class, __getattribute__ is always called first for every attribute access. If the attribute exists in the instance (e.g., in the instance dictionary or via a descriptor), __getattribute__ returns it directly, and __getattr__ is never invoked. __getattr__ is only called as a fallback when __getattribute__ raises an AttributeError. Therefore, for an existing attribute, only __getattribute__ runs, making option D correct.

Answer

__getattr__ always overrides __getattribute__.

Answer

Both __getattr__ and __getattribute__ are called, in that order.

Answer

Only __getattr__ is called.

Question 10

A class defines an __init__ method that takes optional arguments. What is the correct way to provide default values?

Accepted Answer

Use default parameter values in the __init__ signature.. Option A is correct because default parameter values in the method signature are the standard way to provide defaults in Python. Option B, using a separate setter, is unnecessary overhead. Option C, using class variables, would be shared across instances. Option D, using __new__, is not for this purpose.

Answer

Use class variables to store defaults.

Answer

Override __new__ to set default values.

Answer

Use a separate setter method called after instantiation.

Question 11

Which TWO of the following are valid ways to define a class attribute that is shared among all instances?

Accepted Answer

Assign the attribute inside a classmethod using cls.. Option A is correct because a classmethod receives the class (cls) as its first argument, allowing you to assign or modify a class attribute via `cls.attribute = value`. This assignment affects the class itself, making the attribute shared among all instances, as the attribute is stored on the class object, not on instance dictionaries.

Answer

Assign the attribute inside a staticmethod.

Answer

Use the @property decorator.

Answer

Assign the attribute inside __init__ using self.

Question 12

Which TWO statements about inheritance in Python are true?

Accepted Answer

The Method Resolution Order (MRO) is determined by the C3 linearization algorithm.. Option B is correct because Python's Method Resolution Order (MRO) is determined by the C3 linearization algorithm, which ensures a consistent and predictable order for method lookup in multiple inheritance scenarios. This algorithm produces a linearization that respects the local precedence order and monotonicity, as defined in the Python documentation for class hierarchies.

Answer

Abstract base classes can be instantiated if they have no abstract methods.

Answer

Private attributes (with double underscore) of the base class are accessible in the subclass.

Answer

The super() function returns a proxy object for method delegation.

Question 13

Which THREE methods must be implemented to create an immutable object that supports iteration and membership testing?

Accepted Answer

__getitem__. Option B is correct because implementing __getitem__ allows indexing and slicing, which is essential for iteration in Python when __iter__ is not defined; Python falls back to __getitem__ for iteration. This method also supports membership testing via the 'in' operator when __contains__ is absent, as Python will iterate through the object to check membership.

Answer

__init__

Answer

__contains__

Question 14

Refer to the exhibit. What will be the output when the code is executed?

Accepted Answer

2. The code defines a class `MyClass` with a class attribute `x = 1`. The `__init__` method sets an instance attribute `self.x = 2`. When `obj.x` is accessed, Python first looks for an instance attribute, finding `self.x = 2`, so it prints `2`. Option D is correct because instance attributes shadow class attributes.

Answer

AttributeError

Answer

None

Answer

1

Question 15

Refer to the exhibit. What is the root cause of the error?

Accepted Answer

The attribute 'age' is not defined in the class or instance.. Option B is correct because the attribute 'age' is not defined anywhere in the class or instance. Option A is incorrect because there is no private attribute involved. Option C is incorrect because __init__ was called. Option D is incorrect because 'age' is not a class attribute.

Answer

The __init__ method was not called.

Answer

The attribute 'age' is private.

Answer

The attribute 'age' is a class attribute but not initialized.

PCAP Object-Oriented Programming Practice Test 5 — 15 Questions

Exhibit

PCAP Object-Oriented Programming Practice Test 5 — 15 Questions

Exhibit