PCPP2 Hard Questions — 25 Difficult Questions

Question 1

Which TWO of the following are potential issues when using the 'fork' start method in multiprocessing?

Accepted Answer

Threads present in the parent may not be safe in the child.. Forking a process inherits the parent's memory, which can lead to issues with locks and threads.

Answer

It cannot share data at all.

Answer

It crashes on all Unix systems.

Answer

It is always slower than spawn.

Question 2

When using a multiprocessing.Queue to share data between processes, what happens if the queue is full and you use the put() method without a timeout?

Accepted Answer

It blocks indefinitely until a slot becomes available.. By default, put() is a blocking operation that will wait until a slot is available if the queue is full.

Answer

It restarts the child process.

Answer

It raises a Full exception immediately.

Answer

It silently drops the data.

Answer

It overwrites the oldest item in the queue.

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

Two threads are modifying a shared global integer. You want to ensure that only one thread modifies the integer at a time. Which synchronization primitive is most appropriate?

Accepted Answer

threading.Lock. A Lock (or Mutex) is the standard tool to ensure mutually exclusive access to a shared resource.

Answer

threading.Event

Answer

multiprocessing.Semaphore

Answer

multiprocessing.Queue

Answer

threading.Condition

Question 5

When using the multiprocessing module, why is it recommended to use a Manager object instead of a standard dictionary to share data between processes?

Accepted Answer

It ensures the dictionary is synchronized between processes.. A manager process is created to host the objects, allowing them to be shared safely between different processes using proxy objects.

Answer

It is faster than standard dictionaries.

Answer

It is the only way to store strings.

Answer

It removes the need for locks.

Answer

It allows local storage of values.

Question 6

You are using SQLAlchemy's relationship() function. What does 'back_populates' achieve?

Accepted Answer

It synchronizes the two sides of the relationship in Python memory.. It links two sides of a relationship so that changes in one are reflected in the other via the session's identity map.

Answer

It improves query performance.

Answer

It automatically cascades deletes.

Answer

It forces a database level foreign key constraint.

Question 7

What is the primary purpose of the subprocess.PIPE constant?

Accepted Answer

To create a channel for data transfer.. It is used to indicate that a new pipe to the child process should be created for stdout or stdin.

Answer

To terminate the child process.

Answer

To speed up subprocess execution.

Answer

To close the standard input.

Answer

To redirect output to a file.

Question 8

In pytest, how can you dynamically add a marker to a test at runtime?

Accepted Answer

In the pytest_collection_modifyitems hook.. The 'pytest_collection_modifyitems' hook allows you to modify the collected tests, including adding markers dynamically.

Answer

In the __init__ file.

Answer

Using @pytest.mark.add_marker()

Answer

By calling pytest.add_marker() inside the test.

Question 9

Which of the following describes the behavior of TCP_NODELAY?

Accepted Answer

It disables Nagle's algorithm for low-latency communication.. TCP_NODELAY disables Nagle's algorithm, which otherwise buffers small packets to send them as one, reducing network overhead but increasing latency.

Answer

It forces the socket to ignore packet loss.

Answer

It enables UDP-like performance for TCP.

Answer

It increases the packet size to match MTU.

Question 10

Which of these is the most effective way to test a function that uses 'time.sleep()' without actually waiting?

Accepted Answer

Patch 'time.sleep'.. Mocking the 'time.sleep' function prevents it from actually executing the sleep command, making tests run faster.

Answer

Use a faster machine.

Answer

Use pytest.raises.

Answer

Change the sleep duration to 0.

Question 11

Which THREE features are provided by 'pytest' but NOT by the standard 'unittest' framework?

Accepted Answer

Parametrization using markers.. pytest offers native parametrization, powerful fixture injection, and automatic test discovery without boilerplate classes.

Answer

Support for setup and teardown methods.

Answer

Basic assertion support.

Question 12

Which pytest feature allows you to run the same test multiple times with different sets of inputs?

Accepted Answer

@pytest.mark.parametrize. Parametrization using @pytest.mark.parametrize allows a test function to be executed with varying data sets.

Answer

@pytest.mark.repeat

Answer

pytest.loop()

Answer

@pytest.fixture(params=...)

Question 13

Which TWO of the following are common issues when using select.select()?

Accepted Answer

It is inefficient for monitoring thousands of concurrent sockets.. select is limited by the maximum number of file descriptors (FD_SETSIZE) and is not as efficient as epoll/kqueue for massive numbers of connections.

Answer

It requires root privileges to execute.

Answer

It is significantly faster than epoll on all platforms.

Answer

It cannot be used with non-blocking sockets.

Question 14

You are applying the Facade pattern to simplify a complex subsystem consisting of three interacting legacy modules. What is the primary architectural requirement for the Facade class to be effective?

Accepted Answer

The Facade should provide a simplified interface that delegates requests to appropriate subsystem objects. The Facade must act as a single entry point, encapsulating the complexity of the internal modules so the client doesn't need to know about them.

Answer

The Facade must inherit from every class in the subsystem

Answer

The Facade must implement the Singleton pattern to ensure only one interface exists

Answer

The Facade should expose all methods of the subsystem classes for flexibility

Question 15

Which THREE of the following are features of the 'threading' module in Python?

Accepted Answer

Semaphore objects. The threading module provides Locks, Semaphores, and Events for synchronization.

Answer

Shared memory between different processes

Answer

Automatic global interpreter lock removal

Question 16

When using the MongoDB aggregation framework in PyMongo, which stage should be used to filter documents based on a condition?

Accepted Answer

$match. The $match stage is used to filter documents in an aggregation pipeline.

Answer

$group

Answer

$project

Answer

$filter

Question 17

In SQLAlchemy, how do you prevent an object from being saved to the database during a session.commit()?

Accepted Answer

session.expunge(obj). You can use session.expunge(obj) to remove the object from the session's management.

Answer

session.delete(obj)

Answer

session.detach(obj)

Answer

session.rollback()

Question 18

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 19

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 20

Which THREE of the following are true about Python metaclasses?

Accepted Answer

Metaclasses are instances of 'type'. Metaclasses are types, they allow modifying class creation, and they are defined by inheriting from 'type'.

Answer

They are used to create instances directly

Answer

They are required for all classes in Python 3