PCPP2 Advanced OOP And Performance — 15 Questions

Question 1

Which TWO of the following are built-in Python decorators?

Accepted Answer

@classmethod. @staticmethod and @classmethod are built-in decorators for class methods.

Answer

@private

Answer

@final

Answer

@abstractmethod

Question 2

Which THREE of the following are valid ways to define abstract methods in Python?

Accepted Answer

Using the @abstractmethod decorator from 'abc'. The @abstractmethod decorator is the formal way; documentation or raising NotImplementedError are informal/legacy ways.

Answer

Defining the method in an interface file

Answer

Using the @abstract property

Question 3

You are utilizing abstract base classes (ABCs). How do you enforce that a subclass implements a specific method?

Accepted Answer

Use the @abstractmethod decorator. The @abstractmethod decorator marks a method as requiring implementation in concrete subclasses.

Answer

Use a metaclass check

Answer

Raise NotImplementedError in the base class

Answer

Pass the method name to __init__

Question 4

You need to ensure that a class can only be instantiated once throughout the application lifecycle. Which design pattern is most appropriate?

Accepted Answer

Singleton Pattern. The Singleton pattern ensures that a class has only one instance and provides a global point of access to it.

Answer

Factory Pattern

Answer

Adapter Pattern

Answer

Proxy Pattern

Question 5

When writing a context manager using the @contextlib.contextmanager decorator, what should the function do to pass a value to the 'as' clause?

Accepted Answer

Yield the value. The yield statement in a decorated generator function passes the value to the with statement's as target.

Answer

Assign to a global variable

Answer

Use the return statement

Answer

Raise an exception

Question 6

You need to dynamically add methods to a class at runtime. Which mechanism allows you to modify the class object before it is fully constructed?

Accepted Answer

Metaclasses. Metaclasses, specifically the __new__ method, allow for the modification of class creation.

Answer

Inheritance

Answer

Monkey patching

Answer

Class decorators

Question 7

When optimizing Python code, which tool should you use to identify hot spots in the execution path?

Accepted Answer

cProfile. cProfile is the standard built-in profiler in Python for identifying performance bottlenecks.

Answer

pydoc

Answer

pdb

Answer

unittest

Question 8

You are designing a class hierarchy where a subclass needs to ensure it calls the constructor of its parent in a multiple inheritance scenario. Which mechanism is the standard Pythonic approach to handle this dynamically?

Accepted Answer

Using super().__init__(). super() is the standard way to delegate to the next class in the Method Resolution Order (MRO).

Answer

Explicitly calling ParentClass.__init__(self)

Answer

Manually tracking parent states in a registry

Answer

Using the __init__subclass__ hook

Question 9

You have a performance-critical application using heavy objects. You want to reduce memory footprint by preventing the creation of __dict__ for every instance. How should you proceed?

Accepted Answer

Define a __slots__ sequence attribute. Defining __slots__ in a class prevents the creation of __dict__ and __weakref__ for instances, significantly reducing memory usage.

Answer

Use a decorator to delete __dict__ after creation

Answer

Inherit from the object class exclusively

Answer

Set __dict__ = None in the class body

Question 10

You are profiling your code and identify that a specific method is called millions of times. You decide to use a descriptor to optimize attribute access. What must the descriptor implement to intercept attribute assignment?

Accepted Answer

The __set__ method. A data descriptor is defined as an object that implements both __get__ and __set__ (or __delete__).

Answer

The __call__ method

Answer

The __init__ method

Answer

Only the __get__ method

Question 11

You need to compare two objects for equality based on a custom attribute. Which method should you override?

Accepted Answer

__eq__. The __eq__ magic method defines the behavior of the equality operator (==).

Answer

__hash__

Answer

__identical__

Answer

__cmp__

Question 12

You are handling large datasets and want to improve memory efficiency. Which Python feature allows you to iterate over a large sequence without loading it entirely into memory?

Accepted Answer

Generators. Generators provide a lazy evaluation mechanism to yield items one at a time.

Answer

Deepcopy

Answer

Set literals

Answer

List comprehensions

Question 13

Which magic method is used to define how an object is displayed for developers (for debugging)?

Accepted Answer

__repr__. __repr__ is the magic method used to provide an unambiguous string representation of an object.

Answer

__format__

Answer

__str__

Answer

__display__

Question 14

Which built-in function allows you to retrieve an attribute from an object by its string name?

Accepted Answer

getattr(). getattr() is the built-in function to access object attributes dynamically.

Answer

fetch()

Answer

getattribute()

Answer

access()

Question 15

In a multi-threaded application, you need to ensure that shared state is modified safely. Which tool is the most appropriate for this task?

Accepted Answer

threading.Lock. The threading.Lock primitive allows only one thread to access a resource at a time.

Answer

time.sleep

Answer

sys.settrace

Answer

gc.collect