194 questions total · 3pages · All types, answers revealed
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Page 2You are using sqlite3 in Python and need to ensure that data integrity is maintained when performing multiple related INSERT operations. Which method should you call on the connection object to commit your changes?
commit() is the standard method to finalize a transaction in sqlite3.
Why this answer
The commit() method is used to save the current transaction to the database.
You are configuring a server to handle high-concurrency requests. Why is it preferable to use the select.select() module over a simple blocking recv() loop?
select permits waiting for multiple sockets without blocking the thread.
Why this answer
select.select() allows monitoring multiple sockets simultaneously, preventing the server from blocking on a single idle connection.
What is the primary benefit of the Facade pattern when working with legacy libraries?
This is the definition of the Facade pattern.
Why this answer
A Facade simplifies complex library interactions by providing a cleaner, more intuitive interface for the client.
Which Python library is the standard built-in interface for SQLite databases?
sqlite3 is the standard library module.
Why this answer
The 'sqlite3' module is part of the Python standard library.
In a multi-threaded Python server, why is it discouraged to share a single socket object across multiple threads without synchronization?
Shared descriptors without locking can cause race conditions in the application logic.
Why this answer
Socket operations are generally thread-safe in CPython, but overlapping operations on the same file descriptor can lead to interleaved data or corrupted state.
Which TWO of the following are true regarding the socket.shutdown() method?
SHUT_RD stops the input stream.
Why this answer
shutdown() can disable reading, writing, or both, which is useful for protocol-level signaling.
You are utilizing abstract base classes (ABCs). How do you enforce that a subclass implements a specific method?
@abstractmethod ensures the subclass cannot be instantiated without overriding the method.
Why this answer
The @abstractmethod decorator marks a method as requiring implementation in concrete subclasses.
You need to prevent an object's attribute from being modified after it is set. Which approach provides the most robust implementation?
A @property without a @name.setter makes the attribute read-only.
Why this answer
A property with only a getter (or a custom setter that raises an exception) effectively creates a read-only attribute.
You have an object that behaves like a function. Which magic method must be implemented to make this possible?
__call__ turns an object into a callable.
Why this answer
The __call__ method allows an object instance to be invoked as a function.
When implementing the Command pattern in Python, what is a primary advantage of using a 'Command' class hierarchy?
Encapsulation as an object allows for these operations.
Why this answer
It allows commands to be treated as objects, which enables features like queuing, logging, and undo/redo.
In the Decorator pattern, why is it preferred to use the functools.wraps decorator when creating a function decorator?
This is exactly what functools.wraps is designed for.
Why this answer
functools.wraps preserves the metadata (like __name__ and __doc__) of the original function, which is critical for debugging and reflection.
Which of the following is the correct way to close a socket object in Python?
close() is the standard way to release the socket resource.
Why this answer
The close() method should be called on the socket object to release the underlying file descriptor.
When using the 'unittest' framework, which method is executed exactly once before any test methods in a class are run?
This is the correct class method to run setup code once for the entire class.
Why this answer
The 'setUpClass' method is a class method that runs once before all tests in the class, whereas 'setUp' runs before each individual test.
What is the primary purpose of the subprocess.PIPE constant?
PIPE enables interaction with the process streams.
Why this answer
It is used to indicate that a new pipe to the child process should be created for stdout or stdin.
Which method should a developer use to retrieve the IP address and port of the remote peer connected to a TCP socket?
getpeername() is the correct method for remote connection details.
Why this answer
getpeername() returns the address of the remote endpoint connected to the socket.
How do you retrieve the number of documents matched by a PyMongo 'find' operation without fetching all documents into memory?
count_documents is the modern, non-deprecated method.
Why this answer
The count_documents() method on a collection is the recommended way to get a count.
Which module allows you to run external programs and interact with their input/output streams?
Subprocess is the standard for managing processes.
Why this answer
The subprocess module is the recommended way to spawn new processes and connect to their pipes.
Which THREE of the following are common benefits of using a mocking framework in testing?
Core benefit of unit testing.
Why this answer
Mocking isolates the unit under test, speeds up tests by replacing I/O, and enables testing of error paths that are hard to trigger.
In 'unittest.mock', when you want to return a specific value based on the input arguments of a mocked function, which property should be configured?
Assigning a function to side_effect allows dynamic response based on arguments.
Why this answer
The 'side_effect' property allows you to assign a function that computes the return value dynamically based on arguments, unlike 'return_value' which is static.
Which THREE of the following are common characteristics of the Observer pattern?
This is the primary behavior of the pattern.
Why this answer
One-to-many relationship, event notification, and loose coupling are key.
Which of the following is a classic use case for the Builder pattern in Python?
This is the primary purpose of the Builder pattern.
Why this answer
The Builder pattern is ideal when an object requires many steps to construct or has many optional configuration parameters, avoiding 'telescoping constructors'.
You are using a multiprocessing.Semaphore(3). What happens when the 4th process attempts to acquire the semaphore?
This is the standard behavior for a semaphore.
Why this answer
The 4th process will block until one of the previous three processes releases the semaphore.
Which THREE of the following are valid scopes for a pytest fixture?
Default scope.
Why this answer
The valid scopes in pytest are function, class, module, package, and session.
Which TWO of the following are necessary to connect a TCP client to a server?
Required to create the socket object.
Why this answer
The client must have an instantiated socket and call connect() with the correct target address tuple.
Which TWO of the following are true regarding 'unittest' test suites?
Inheritance is required for the framework to pick up the tests.
Why this answer
Suites can be built using TestLoader, and tests are aggregated from classes inheriting from unittest.TestCase.
You are writing a Python script that needs to perform heavy I/O-bound tasks concurrently. Which module should you prioritize to minimize the overhead of global interpreter lock (GIL) contention?
Threading is efficient for I/O-bound tasks because it allows concurrent waiting.
Why this answer
The threading module is ideal for I/O-bound tasks as it releases the GIL during blocking operations, whereas multiprocessing is better for CPU-bound tasks.
Which pytest feature allows you to run the same test multiple times with different sets of inputs?
This is the built-in way to run tests with multiple inputs.
Why this answer
Parametrization using @pytest.mark.parametrize allows a test function to be executed with varying data sets.
If you want to run a function in a background thread, which class should you instantiate?
The Thread class is for spawning threads.
Why this answer
The threading.Thread class is the standard way to create threads.
Which THREE of the following options can be used with socket.setsockopt()?
Enables keep-alive packets.
Why this answer
SO_REUSEADDR, SO_KEEPALIVE, and TCP_NODELAY are standard options supported by most systems.
You need to ensure that a class can only be instantiated once throughout the application lifecycle. Which design pattern is most appropriate?
Singleton restricts instantiation to a single object.
Why this answer
The Singleton pattern ensures that a class has only one instance and provides a global point of access to it.
When managing resources like file handles, what is the best practice to ensure they are always closed?
The with statement guarantees resource release.
Why this answer
The with statement (context manager) ensures that cleanup code is executed regardless of exceptions.
Which TWO of the following are structural patterns?
Facade is a structural pattern.
Why this answer
Adapter and Facade are classic structural patterns.
What is the effect of setting a socket to non-blocking mode using socket.setblocking(False)?
Operations that cannot complete immediately throw a BlockingIOError.
Why this answer
Non-blocking sockets cause operations like recv() and connect() to raise an exception if they cannot be completed immediately.
Which of the following best describes the benefit of using parameterized queries in sqlite3?
Parameterized queries ensure input is treated as data, not code.
Why this answer
Parameterized queries prevent SQL injection by separating the query logic from the data.
When implementing the Bridge pattern, what is the primary structural requirement to effectively decouple an abstraction from its implementation?
This composition allows the implementation to be swapped at runtime.
Why this answer
The abstraction must contain a reference (bridge) to an object of an implementor interface, allowing the implementation to vary independently.
Which object would you use to share a simple integer between processes that is safe for concurrent access?
Value provides shared memory access to a variable.
Why this answer
multiprocessing.Value is designed specifically to share single values between processes with a lock.
Which THREE features are provided by 'pytest' but NOT by the standard 'unittest' framework?
pytest has this built-in.
Why this answer
pytest offers native parametrization, powerful fixture injection, and automatic test discovery without boilerplate classes.
Which THREE of the following are true regarding the use of the socket module in Python?
Sockets are file-like objects backed by OS descriptors.
Why this answer
Sockets are file descriptors, they can be set to non-blocking mode, and they must be closed to avoid resource leaks.
When using inheritance, how can you explicitly call a method from a specific parent class that is not the immediate superclass?
Direct invocation on the class bypasses the MRO.
Why this answer
Calling the method directly on the class object (e.g., Parent.method(self)) bypasses the MRO.
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?
Delegation is the key mechanism of the Facade pattern to hide complexity.
Why this answer
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.
Handshaking and flow control add overhead to TCP.
Which pattern is most appropriate for a scenario where you want to provide a standard interface for a suite of related or dependent objects without specifying their concrete classes?
Abstract Factory is specifically designed for families of related objects.
Why this answer
The Abstract Factory pattern provides an interface for creating families of related objects.
Which TWO of the following scenarios are best suited for the subprocess module?
Executing external binaries is a primary use case.
Why this answer
Subprocess is intended for executing external binaries and interacting with their system streams.
In sqlite3, how do you handle a database error such as a constraint violation?
sqlite3 raises specific exceptions for database errors.
Why this answer
You should wrap database operations in a try-except block and catch sqlite3.Error or its subclasses.
Which TWO of the following are valid ways to run tests?
Standard unittest module command.
Why this answer
Both 'pytest' and 'python -m unittest' are the standard command-line ways to execute Python test suites.
You need to implement a custom class that behaves like a sequence, allowing indexing and length checking. Which magic methods are required?
These two methods allow indexing and length retrieval.
Why this answer
To be a sequence, a class needs to implement __getitem__ and __len__.
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?
Default behavior of put() is to block if the queue is full.
Why this answer
By default, put() is a blocking operation that will wait until a slot is available if the queue is full.
Which TWO of these are valid parameters for the MongoClient constructor?
The host parameter is valid.
Why this answer
MongoClient accepts host and port, or a connection string.
Why is the socket.socket() constructor typically called with socket.AF_INET and socket.SOCK_STREAM for a standard web server?
SOCK_STREAM is the identifier for the TCP protocol.
In a multi-threaded application, you need to ensure that shared state is modified safely. Which tool is the most appropriate for this task?
Locks provide mutual exclusion to prevent race conditions.
Why this answer
The threading.Lock primitive allows only one thread to access a resource at a time.
What is the purpose of the 'upsert=True' option in MongoDB update operations?
Upsert is a combination of update and insert.
Why this answer
If no document matches the query, a new document is created with the update criteria.
When writing a metaclass, what is the 'cls' parameter in the __new__ method referring to?
The first argument to __new__ in a metaclass is the metaclass type.
Why this answer
In a metaclass's __new__ method, 'cls' refers to the metaclass itself, not the class being created.
Which TWO of the following are valid ways to assert that a mock was NOT called?
Explicit method for this purpose.
Why this answer
assert_not_called and assert_called_count(0) are both valid methods to confirm a mock was not interacted with.
You have a thread waiting on a threading.Event. Which method should another thread call to wake up the waiting thread?
Set() triggers the Event.
Why this answer
The set() method sets the internal flag to true, causing wait() to return.
Which THREE of the following are features of the 'threading' module in Python?
Semaphores are supported for resource counting.
Why this answer
The threading module provides Locks, Semaphores, and Events for synchronization.
Which THREE of the following are benefits of the Factory Method pattern?
New product types can be added by creating new creators without changing existing code.
Why this answer
Decoupling, Open/Closed adherence, and centralized logic are the main benefits.
When using the multiprocessing module, why is it recommended to use a Manager object instead of a standard dictionary to share data between processes?
The manager provides a proxy that handles the necessary IPC.
Why this answer
A manager process is created to host the objects, allowing them to be shared safely between different processes using proxy objects.
Which THREE of the following are standard ways to implement the 'Strategy' pattern in Python?
Dependency injection is standard for the Strategy pattern.
Why this answer
Using functions, classes, or dependency injection are all valid strategies.
Which of the following is true regarding daemon threads in Python?
Daemon threads are force-stopped by the interpreter.
Why this answer
Daemon threads are terminated abruptly when the main program exits, which can lead to incomplete operations.
You need to detect if a client has disconnected from your TCP server. What is the standard behavior of recv() when the peer performs a clean shutdown?
An empty bytes object is the indicator of an orderly EOF in TCP.
Why this answer
A clean shutdown by the peer causes recv() to return an empty bytes object (b'').
Which operator is used to perform bitwise AND operations?
& performs bitwise AND.
Why this answer
The & operator is the bitwise AND operator in Python.
Which of these is the most effective way to test a function that uses 'time.sleep()' without actually waiting?
Mocking the function avoids the delay entirely.
Why this answer
Mocking the 'time.sleep' function prevents it from actually executing the sleep command, making tests run faster.
Which of the following describes the behavior of TCP_NODELAY?
This allows small packets to be sent without waiting for buffer filling.
Why this answer
TCP_NODELAY disables Nagle's algorithm, which otherwise buffers small packets to send them as one, reducing network overhead but increasing latency.
In the Memento pattern, which component is responsible for storing the state of the Originator without exposing its internal structure?
The Memento object stores the state effectively acting as a snapshot.
Why this answer
The Memento object acts as an opaque carrier of the state, ensuring the Originator's internals remain private.
You are implementing a custom type in SQLAlchemy. Which method must be overridden to convert data from the database type back to a Python object?
This converts DB results into Python objects.
Why this answer
The process_result_value method is responsible for type conversion during retrieval.
Which object in SQLAlchemy is responsible for maintaining a collection of loaded objects and managing their lifecycle?
The session tracks object states like 'persistent' and 'dirty'.
Why this answer
The Session object acts as a workspace for objects and tracks their state.
Which function in the socket module is used to convert a 32-bit integer from host byte order to network byte order?
htonl is used for 32-bit integer conversion.
Why this answer
htonl() stands for Host to Network Long, converting 32-bit integers for network transmission.
You are using SQLAlchemy with an asynchronous driver (asyncio). Which object must be used to perform database operations asynchronously?
AsyncSession supports awaitable methods for database access.
Why this answer
AsyncSession is the required class for asynchronous session management in SQLAlchemy.
Which THREE of these are valid relationship loading strategies in SQLAlchemy?
Subquery loading uses a separate query with a subselect.
Why this answer
lazy, joined, and subquery are three common loading strategies.
In SQLAlchemy, what does the 'metadata.create_all(engine)' command do?
This is the primary function of create_all.
Why this answer
It inspects the defined ORM models and emits CREATE TABLE statements to the database.
Which TWO of the following are key benefits of using the multiprocessing.Pool class?
Pool manages the process lifecycle.
Why this answer
Pools simplify process management and provide convenient result retrieval mechanisms.
When using the sqlite3 module, what is the primary purpose of using a context manager (the 'with' statement) on a connection object?
The 'with' statement handles transaction control automatically.
Why this answer
In sqlite3, the connection context manager automatically commits or rolls back transactions.
Which TWO are common pitfalls when working with SQLite databases in a multi-threaded environment?
Standard sqlite3 connections are not thread-safe.
Why this answer
SQLite connections are not thread-safe by default, and lock contention can occur.
You are handling large datasets and want to improve memory efficiency. Which Python feature allows you to iterate over a large sequence without loading it entirely into memory?
Generators yield values on demand, saving memory.
Why this answer
Generators provide a lazy evaluation mechanism to yield items one at a time.
Which THREE of the following represent types of IPC provided by the multiprocessing module?
Pipes provide a connection between two processes.
Why this answer
Multiprocessing provides Pipes, Queues, and Managers for inter-process communication.
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Target a specific domain to shore up weak areas.