PCPP2 Practice Test 2 — 30 Questions

Question 1

When using subprocess.Popen, why is it dangerous to use shell=True with user-supplied input?

Accepted Answer

It leads to shell command injection vulnerabilities.. It introduces a command injection vulnerability where a user can execute arbitrary shell commands.

Answer

It prevents capturing stderr.

Answer

It slows down execution significantly.

Answer

It crashes the Python interpreter.

Answer

It forces the use of hardcoded paths.

Question 2

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 3

Which module allows you to run external programs and interact with their input/output streams?

Accepted Answer

subprocess. The subprocess module is the recommended way to spawn new processes and connect to their pipes.

Answer

sys

Answer

multiprocessing

Answer

os

Answer

threading

Question 4

If you want to run a function in a background thread, which class should you instantiate?

Accepted Answer

threading.Thread. The threading.Thread class is the standard way to create threads.

Answer

threading.Process

Answer

subprocess.Thread

Answer

multiprocessing.Thread

Answer

thread.Task

Question 5

Which THREE of the following are valid ways to instantiate a process in the multiprocessing module?

Accepted Answer

By subclassing multiprocessing.Process.. Process can be instantiated directly, via target function, or by subclassing.

Answer

Using the multiprocessing.Queue method.

Answer

Using the threading.Thread class.

Question 6

Which of the following is a classic use case for the Builder pattern in Python?

Accepted Answer

Constructing complex objects step-by-step with various configurations. The Builder pattern is ideal when an object requires many steps to construct or has many optional configuration parameters, avoiding 'telescoping constructors'.

Answer

Adding new behaviors to an object at runtime

Answer

Creating a simple object with no parameters

Answer

Ensuring only one instance of a class exists

Question 7

You are implementing the Command pattern. How can you best support the 'Undo' operation for a command that changes a document's state?

Accepted Answer

Store the delta or previous state information within the concrete command instance. The Command object must store the previous state or the inverse operation before performing the change, allowing it to revert the state later.

Answer

Use the Python 'copy' module to clone the document before every command

Answer

Store the entire document object in the command history

Answer

Re-execute the entire command history up to the point of the undo

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

You are implementing a Proxy pattern to provide lazy initialization for a resource-heavy object. Which technique is most effective for checking if the real object exists without triggering its constructor prematurely?

Accepted Answer

Check if the object attribute is None before calling the constructor. The Proxy should hold a reference to the real object and only instantiate it when a method is called that requires the real object's functionality.

Answer

Use the @property decorator to trigger instantiation immediately upon object creation

Answer

Overload the __del__ method to release the resource

Answer

Use a try-except block around the Proxy's constructor

Question 10

You are implementing a Singleton pattern in Python using a metaclass. Which mechanism ensures that the __call__ method of the metaclass is only executed once for a specific class?

Accepted Answer

Implementing a dictionary within the metaclass to cache and return existing instances. The metaclass __call__ method controls instance creation. By using a dictionary within the metaclass to store existing instances, you ensure that subsequent calls return the cached instance.

Answer

Setting the class variable __instance__ to None in the global scope

Answer

Overriding the __init__ method of the object class

Answer

Using the __new__ method of the target class instead of the metaclass

Question 11

You are refactoring a legacy module and want to use 'pytest' to check if a function raises a specific custom exception. Which construct is most idiomatic?

Accepted Answer

with pytest.raises(CustomError):. The 'pytest.raises' context manager is the standard way to verify that a block of code raises a specific exception type.

Answer

pytest.catch(CustomError)

Answer

assert func() == CustomError

Answer

with pytest.assert_raises(CustomError):

Question 12

Which of the following is a valid way to run all tests in a directory using pytest?

Accepted Answer

pytest. Running 'pytest' without arguments in a directory defaults to discovering and executing all tests in that directory tree.

Answer

pytest --all

Answer

python -m unittest discover

Answer

pytest --execute-all

Question 13

In pytest, how can you share a fixture across multiple files?

Accepted Answer

Place it in conftest.py.. Placing the fixture in a 'conftest.py' file within a directory makes it available to all test files in that directory and subdirectories.

Answer

Define it in __init__.py.

Answer

Use the --shared-fixtures flag.

Answer

Import it in every file.

Question 14

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 15

You are writing a pytest fixture that opens a database connection. Which scope should you use to ensure the connection is created once per module, rather than once per test function?

Accepted Answer

scope='module'. The 'scope' argument in the @pytest.fixture decorator controls the lifetime. 'module' scope runs the fixture once per module.

Answer

scope='class'

Answer

scope='function'

Answer

scope='session'

Question 16

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 17

You are writing a UDP server. What is the main disadvantage of using UDP for high-volume data transmission compared to TCP?

Accepted Answer

UDP does not provide delivery guarantees or ordering.. UDP provides no guarantee of delivery, order, or congestion control, requiring the application to handle these issues.

Answer

UDP packets are always larger than TCP packets.

Answer

UDP requires more handshake overhead.

Answer

UDP is not supported on all operating systems.

Question 18

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 19

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 20

What is the significance of the SO_BROADCAST option in a UDP socket?

Accepted Answer

It enables the socket to send packets to a broadcast address.. SO_BROADCAST is a prerequisite for sending packets to the broadcast address on a network interface.

Answer

It allows the socket to handle incoming multicast traffic.

Answer

It allows the socket to listen to all ports on a machine.

Answer

It makes the socket connection-oriented.