PCPP2 Practice Test 4 — 10 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