PCPP1 Hard Questions — 25 Difficult Questions

Question 1

You are developing a multithreaded HTTP scraper. When using the 'requests' library inside 'threading.Thread' objects, what is the recommended practice for handling session persistence?

Accepted Answer

Initialize a new Session object inside each thread's run method. The requests.Session object is not thread-safe because it maintains shared state such as cookies, connection pools, and headers. Initializing a new Session inside each thread's run method ensures each thread has its own isolated session, avoiding race conditions and data corruption. This is the recommended practice for multithreaded scraping with requests.

Answer

Wrap the session object in a threading.Lock

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Share a single global Session object across all threads

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Disable connection pooling using 'pool_connections=0'

Question 2

You are refactoring code that performs sensitive operations. Which of the following is the most secure practice for handling secret keys?

Accepted Answer

Use environment variables to store sensitive configuration.. Hardcoding secrets is a major security vulnerability; using environment variables is the industry standard.

Answer

Encrypt the secrets and store them as constants in a module.

Answer

Store secrets in a private class attribute.

Answer

Hardcode them as strings inside a 'config.py' file and ignore it in Git.

Question 3

You are writing a Python utility that copies a directory tree to a network share using shutil. You must preserve file metadata and fail loudly if the destination already contains a conflicting file, rather than silently overwriting it. Which TWO shutil features satisfy these requirements? (Choose two.)

Accepted Answer

Leave the default behaviour of shutil.copytree() unchanged so that a pre-existing destination path raises FileExistsError.. Preserving metadata requires a copy function built on copystat, which copy2 provides, and copytree() exposes this through copy_function. Failing loudly on a pre-existing destination is the default copytree() behaviour, since dirs_exist_ok is False unless explicitly set. Together, copy_function=shutil.copy2 and the default dirs_exist_ok value satisfy both stated requirements.

Answer

Pass copy_function=shutil.copyfile to shutil.copytree() so existing files are never overwritten.

Answer

Pass dirs_exist_ok=True to shutil.copytree() so the copy proceeds when the destination directory already exists.

Answer

Pass copy_function=shutil.copy to shutil.copytree() so only permission bits are carried over.

Question 4

You are designing a REST client that must call an endpoint protected by OAuth 2.0 using the client credentials grant. The authorization server expects the client identifier and client secret to be sent in the request body as `application/x-www-form-urlencoded`, along with `grant_type=client_credentials`. Which `requests` call correctly obtains the token?

Accepted Answer

requests.post(token_url, data={'grant_type': 'client_credentials', 'client_id': cid, 'client_secret': secret}). OAuth 2.0 token requests use POST with application/x-www-form-urlencoded bodies. The data parameter in requests performs that encoding automatically. Sending the grant type and client credentials in the body, rather than as Basic auth or JSON, satisfies the server's stated expectations and returns the access token needed for subsequent API calls.

Answer

requests.post(token_url, json={'grant_type': 'client_credentials', 'client_id': cid, 'client_secret': secret})

Answer

requests.post(token_url, auth=(cid, secret), data={'grant_type': 'client_credentials'})

Answer

requests.get(token_url, params={'grant_type': 'client_credentials', 'client_id': cid, 'client_secret': secret})

Question 5

What is the effect of setting __slots__ in a parent class on a child class that does not define its own __slots__?

Accepted Answer

The child class will have a __dict__ attribute, overriding the parent's optimization.. The child class will receive an instance __dict__ unless it also defines __slots__, effectively defeating the memory optimization of the parent.

Answer

The child class will raise an error at instantiation.

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The child class will inherit the memory savings automatically.

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The child class will be unable to add new attributes.

Question 6

In Python socket programming, what does the 'SO_REUSEADDR' socket option achieve?

Accepted Answer

It allows the address to be reused immediately after the server stops. It allows the socket to bind to a port that is in a TIME_WAIT state, commonly used to restart servers quickly.

Answer

It speeds up data transmission

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It enables broadcasting on the socket

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It prevents the socket from closing

Question 7

You are building a Python script that needs to create a ZIP archive containing files from a directory. You want to preserve the directory structure inside the archive. Which approach using the zipfile module correctly adds the file '/data/reports/summary.txt' as 'reports/summary.txt' inside the archive?

Accepted Answer

zipf.write('/data/reports/summary.txt', arcname='reports/summary.txt'). The zipfile.ZipFile.write() method accepts an arcname parameter that specifies the name of the file inside the archive. To preserve a directory structure, you provide a relative path as the arcname, such as 'reports/summary.txt'. This ensures the file is stored with that exact path, regardless of its location on the filesystem.

Answer

zipf.write('/data/reports/summary.txt')

Answer

zipf.add('/data/reports/summary.txt', 'reports/summary.txt')

Answer

zipf.write('/data/reports/summary.txt', arcname='summary.txt')

Question 8

Which TWO of the following statements about the Python 'requests' library are correct?

Accepted Answer

It uses 'urllib3' internally for connection pooling. Option A is correct because the requests library is built on top of urllib3, which provides the underlying connection pooling and HTTP transport capabilities. Option E is correct because when you call requests.get() or similar top-level functions without using a Session object, requests creates a temporary Session internally, performs the request, and then closes the connection rather than reusing it. Option B is incorrect because requests fully supports HTTPS and TLS/SSL verification. Option C is incorrect because requests is a third-party package that must be installed via pip, not part of the Python standard library. Option D is incorrect because requests is not guaranteed thread-safe for all operations; while Session objects can be used across threads with care, the library does not provide blanket thread-safety guarantees.

Answer

It does not support HTTPS

Answer

It is part of the standard library

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It is thread-safe by default for all operations

Question 9

You are using 'concurrent.futures.ThreadPoolExecutor' to fetch data from multiple REST APIs. What happens if an exception is raised inside a thread?

Accepted Answer

The exception is stored and raised when calling future.result(). Exceptions raised in a future are captured and re-raised when calling result() on the Future object returned by submit().

Answer

The exception is ignored by the ThreadPoolExecutor

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The entire program crashes immediately

Answer

The thread dies silently without notification

Question 10

Which THREE of the following are valid ways to pass arguments to a function called by a Tkinter button command?

Accepted Answer

command=lambda arg=arg1: my_func(arg). Option A is correct because a lambda with a default argument (arg=arg1) captures the value at definition time and passes it to my_func when the button is clicked, avoiding late-binding issues. Option B is correct because a zero-argument lambda that closes over arg1 defers execution of my_func(arg1) until the button is pressed, which is the standard Tkinter pattern for passing arguments. Option C is correct because functools.partial(my_func, arg1) creates a callable that already has arg1 bound, and Tkinter accepts any callable as the command. Option D is wrong because my_func(arg1=value) is invoked immediately at widget creation, so command receives the function's return value rather than a callable. Option E is wrong for the same reason: my_func(arg1) executes right away and its result is assigned to command, not deferred until the button is clicked.

Answer

command=my_func(arg1=value)

Answer

command=my_func(arg1)

Question 11

You are developing a Python script that needs to determine the absolute path of a file located in a directory relative to the script's location. You decide to use the os.path module. Which of the following functions should you use to obtain the absolute path without resolving symbolic links?

Accepted Answer

os.path.abspath(). os.path.abspath() computes an absolute path by combining the current working directory with the given path, normalizing it without resolving symbolic links. This matches the requirement. os.path.realpath() would resolve symlinks, os.path.normpath() only normalizes, and os.path.join() only concatenates components. Thus, abspath is the correct choice.

Answer

os.path.normpath()

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os.path.realpath()

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os.path.join()

Question 12

You are using configparser.ConfigParser to read a configuration file. You have a file where option names are case-sensitive. How do you ensure the parser respects this casing?

Accepted Answer

parser.optionxform = lambda x: x. By default, ConfigParser converts keys to lowercase. You must override the optionxform method of the parser instance.

Answer

parser = ConfigParser(case_sensitive=True)

Answer

parser.set_case(True)

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parser.read(file, case='preserve')

Question 13

If you define a class with a metaclass that has a custom __call__ method, when is that __call__ method executed?

Accepted Answer

When an instance of the class is created.. The metaclass's __call__ method is invoked whenever the class created by that metaclass is instantiated (i.e., when you call the class name like MyClass()).

Answer

Every time an instance method is called.

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When the metaclass is first imported.

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When the class itself is defined.

Question 14

You are designing a Python application that consumes a REST API which returns JSON data. The API responses can be large, and you need to process the JSON incrementally to avoid loading the entire response into memory. The server supports chunked transfer encoding. Which of the following techniques should you use with the 'requests' library to stream the response and parse it incrementally?

Accepted Answer

Set stream=True in the request and use response.iter_content() to read chunks, then parse each chunk with a streaming JSON parser like ijson.. To process large JSON responses incrementally with 'requests', you must enable streaming with 'stream=True' and then read the response in chunks using 'response.iter_content()'. Since JSON is not inherently line-delimited, you need a streaming parser like 'ijson' to parse the chunks as they arrive. This avoids loading the entire response into memory, making it suitable for large datasets.

Answer

Use response.json() directly; it automatically streams and parses the JSON without loading everything into memory.

Answer

Use requests.get() with a large timeout and rely on the operating system's memory management to handle the response.

Answer

Set stream=True and then call response.json() to parse the streamed data.

Question 15

You are implementing a REST API client in Python using the 'requests' library. The API requires authentication using OAuth 2.0. You need to obtain an access token and then use it to authenticate subsequent requests. Which TWO of the following statements about handling OAuth 2.0 with 'requests' are correct? (Choose two.)

Accepted Answer

You can use the 'requests-oauthlib' library to handle the OAuth 2.0 flow, including token refresh.. Handling OAuth 2.0 with 'requests' typically involves either using a specialized library like 'requests-oauthlib' for full flow management, or manually adding the Bearer token to the Authorization header if you already have a valid token. The core 'requests' library does not provide built-in OAuth 2.0 support, and sending tokens as query parameters is insecure and not recommended.

Answer

OAuth 2.0 access tokens are typically sent as query parameters in the URL.

Answer

The 'requests' library automatically refreshes expired OAuth 2.0 tokens when using the 'auth' parameter.

Answer

The 'requests' library includes built-in support for OAuth 2.0 token management.

Question 16

Which TWO of the following are secure coding practices in Python?

Accepted Answer

Avoid using 'pickle' for untrusted data.. Option C is correct because Python's 'pickle' module is inherently unsafe for untrusted data: unpickling executes arbitrary code via the __reduce__ method, so deserializing attacker-controlled bytes can lead to remote code execution; safe alternatives include 'json' or other non-executable formats. Option D is correct because validating and sanitizing all user input (e.g., using allowlists, type checks, and parameterized queries) prevents injection flaws such as SQL injection, command injection, and XSS, forming a core secure coding practice. Option A is wrong because 'subprocess' with 'shell=True' passes the command through the shell, enabling shell metacharacter injection; the safe practice is 'shell=False' with an argument list. Option B is wrong because 'eval()' executes arbitrary Python expressions and is a classic code-injection vector; dynamic execution should use safer mechanisms like 'ast.literal_eval' for literals. Option E is wrong because hardcoded credentials in source code expose secrets and violate secure secret-management practices such as using environment variables or a secrets manager.

Answer

Use 'subprocess' with 'shell=True'.

Answer

Always use 'eval()' for dynamic execution.

Answer

Use hardcoded credentials for database connections.

Question 17

Which TWO of these identify a potential 'code smell' in Python exception handling?

Accepted Answer

Swallowing exceptions with an empty 'except' block.. Option B is a code smell because an empty 'except:' block silently swallows every exception, hiding failures and making debugging nearly impossible; at minimum the handler should log or re-raise. Option D is a code smell because 'BaseException' includes 'SystemExit', 'KeyboardInterrupt', and 'GeneratorExit', so catching it can prevent normal interpreter shutdown and interrupt handling; application code should normally catch 'Exception' or more specific subclasses. Option A is not a smell: 'finally' is the correct construct for guaranteed cleanup such as closing files or releasing locks. Option C is not a smell: catching specific exception types is the recommended practice for precise, safe error handling. Option E is not a smell: defining and raising custom exceptions improves clarity and lets callers handle domain-specific errors.

Answer

Using 'finally' for cleanup.

Answer

Catching specific exceptions.

Answer

Raising custom exceptions.

Question 18

You are building a custom HTTP client and need to handle persistent connections (keep-alive). What is the primary role of the 'Connection' header?

Accepted Answer

To request the reuse of the TCP connection. The 'Connection: keep-alive' header tells the server that the client wants to reuse the same TCP connection for multiple requests.

Answer

To signal that the server is alive

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To encrypt the connection

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To set the timeout for the connection

Question 19

Why does the 'abc' module provide the 'ABCMeta' metaclass?

Accepted Answer

To enforce abstract method implementation at instantiation.. ABCMeta is the metaclass that implements the logic to prevent instantiation of classes with abstract methods.

Answer

To allow private methods.

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To improve method resolution speed.

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To support multiple inheritance.

Question 20

What happens if you use a decorator on a class that returns a modified version of the class?

Accepted Answer

The original class object is replaced.. The class name, module, and other attributes might be replaced, which can confuse introspection tools; functools.wraps is usually not applicable to classes.

Answer

It triggers a SyntaxError.

Answer

The class cannot be instantiated.

Answer

The metaclass is ignored.