PCPP2 Practice Test 13 — 15 Questions

Question 1

In sqlite3, how do you handle a database error such as a constraint violation?

Accepted Answer

Use a try-except block to catch sqlite3.Error.. You should wrap database operations in a try-except block and catch sqlite3.Error or its subclasses.

Answer

Check the connection status after every query.

Answer

Check the return value of the execute() method.

Answer

The library crashes the program automatically.

Question 2

Which TWO are common pitfalls when working with SQLite databases in a multi-threaded environment?

Accepted Answer

Sharing a single connection object across threads. SQLite connections are not thread-safe by default, and lock contention can occur.

Answer

Memory leaks in the cursor object

Answer

SQL injection via parameterized queries

Answer

Incorrect SQL syntax

Question 3

Which THREE attributes of 'unittest.mock.Mock' allow for verifying call interactions?

Accepted Answer

call_args_list. call_args, call_args_list, and method_calls provide metadata about how the mock was interacted with during a test.

Answer

return_value

Answer

side_effect

Question 4

In SQLAlchemy, what is the difference between 'lazy='select'' and 'lazy='joined'' loading strategies?

Accepted Answer

select loading executes a separate SQL statement when the attribute is first accessed.. joined loading performs an outer join to fetch related objects in the same query, whereas select loading fetches them only when accessed.

Answer

joined loading causes N+1 query problems.

Answer

joined loading is always faster.

Answer

select loading is the default for all relationships.

Question 5

What is the purpose of the 'upsert=True' option in MongoDB update operations?

Accepted Answer

It creates a new document if no match is found.. If no document matches the query, a new document is created with the update criteria.

Answer

It prevents duplicates.

Answer

It sorts the results before updating.

Answer

It forces an atomic update across a cluster.

Question 6

In SQL, which clause is used to filter results based on a condition after grouping?

Accepted Answer

HAVING. The HAVING clause filters aggregated data, whereas WHERE filters raw data.

Answer

WHERE

Answer

ORDER BY

Answer

GROUP BY

Question 7

Which THREE of these are valid relationship loading strategies in SQLAlchemy?

Accepted Answer

subquery. lazy, joined, and subquery are three common loading strategies.

Answer

eager

Answer

direct

Question 8

In the Memento pattern, which component is responsible for storing the state of the Originator without exposing its internal structure?

Accepted Answer

The Memento. The Memento object acts as an opaque carrier of the state, ensuring the Originator's internals remain private.

Answer

The Caretaker

Answer

The Originator's public properties

Answer

A global database

Question 9

You are using the Composite pattern to represent a tree structure of UI elements. What is the most critical challenge when implementing a 'get_parent' method in this pattern?

Accepted Answer

It requires the base Component class to store a reference to the parent. The Composite pattern typically flows downward; maintaining an upward reference (parent pointer) creates bidirectional dependencies that make removing or moving nodes complex.

Answer

It requires the Leaf objects to also implement the same parent reference logic

Answer

It makes the children too independent

Answer

Python's memory management cannot handle circular references

Question 10

What is the primary benefit of the Facade pattern when working with legacy libraries?

Accepted Answer

It provides a simplified, unified interface to a complex subsystem. A Facade simplifies complex library interactions by providing a cleaner, more intuitive interface for the client.

Answer

It increases the performance of the underlying legacy library

Answer

It automatically patches security vulnerabilities in legacy code

Answer

It allows you to rewrite the legacy code

Question 11

Which TWO of the following are components of the Model-View-Controller (MVC) pattern frequently seen in Python web frameworks?

Accepted Answer

Model. The Model (data) and View (representation) are core, while Controllers or View-models mediate.

Answer

Strategy

Answer

Facade

Answer

Observer

Question 12

When implementing the Strategy pattern, what is the best way to inject the strategy into the context object?

Accepted Answer

Pass the strategy instance to the context's constructor. Dependency injection, usually via the constructor, allows the context to remain agnostic of the specific strategy implementation.

Answer

Use a global variable for the strategy

Answer

Import the strategy module inside the context's run method

Answer

Hardcode the strategy class inside the context's __init__ method

Question 13

You are implementing the Visitor pattern to add operations to a set of stable class structures. Why is the 'Double Dispatch' mechanism essential?

Accepted Answer

It resolves the method call based on the runtime types of both the visitor and the element. Double dispatch ensures that the correct method is executed based on both the type of the Visitor and the type of the Element being visited.

Answer

It prevents the element from needing to know about the visitor

Answer

It allows the visitor to access private methods of the element

Answer

It allows the visitor to be defined as a singleton

Question 14

What is the purpose of the 'autospec' argument in 'patch'?

Accepted Answer

It creates a mock with the same API as the original object.. autospec ensures the mock has the same attributes and methods as the object it is replacing, preventing tests from passing when they call non-existent methods.

Answer

It speeds up test execution.

Answer

It automatically generates a return value.

Answer

It automatically documents the mock calls.

Question 15

What is the purpose of 'pytest.mark.xfail'?

Accepted Answer

To allow a known failure to not break the build.. It marks a test as expected to fail, allowing the build to pass even if the test fails.

Answer

To debug a failing test.

Answer

To force a test to fail.

Answer

To skip a test temporarily.