PCPP2 Practice Test 7 — 10 Questions

Question 1

You want to store an object in a set. What must the object implement?

Accepted Answer

__hash__ and __eq__. To be hashable (and thus stored in a set), an object must implement __hash__ and have equality defined via __eq__.

Answer

__iter__

Answer

__set__

Answer

__init__ only

Question 2

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 3

When using the sqlite3 module, what is the primary purpose of using a context manager (the 'with' statement) on a connection object?

Accepted Answer

To automatically commit or rollback transactions.. In sqlite3, the connection context manager automatically commits or rolls back transactions.

Answer

To lock the database file for exclusive access.

Answer

To automatically close the connection upon exit.

Answer

To parse SQL queries for syntax errors.

Question 4

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 5

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 6

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 7

You are developing an application using SQLAlchemy and need to retrieve a single object by its primary key. Which method is preferred for this operation?

Accepted Answer

session.get(Model, pk). The get() method on the Session object is the optimized way to retrieve an object by its primary key.

Answer

Model.find(pk)

Answer

session.fetch(Model, pk)

Answer

session.query(Model).filter(Model.id == pk).first()

Question 8

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 9

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

Question 10

You are using a multiprocessing.Pool. Which method should you use to apply a function to a sequence of items and get the results back in order as they complete?

Accepted Answer

imap(). imap() returns an iterator that yields results in the order of the inputs.

Answer

apply()

Answer

map_async()

Answer

map()

Answer

starmap()