PCPP1 Hard Questions — 25 Difficult Questions

Question 1

A script processes data from untrusted sources. Which technique best mitigates 'pickle' deserialization vulnerabilities?

Accepted Answer

Use an alternative format like JSON or XML for serialization.. The 'pickle' module is fundamentally insecure; using secure formats like JSON is the only way to avoid code injection during deserialization.

Answer

Only unpickle from files with a specific extension.

Answer

Wrap the unpickling in a try-except block.

Answer

Use 'pickle.load()' with a restricted whitelist of modules.

Question 2

In the context of writing robust error handling, what is the 'EAFP' principle?

Accepted Answer

Easier to Ask for Forgiveness than Permission.. EAFP stands for 'Easier to Ask for Forgiveness than Permission', which encourages using try-except blocks instead of pre-checking states.

Answer

Ensure All Functions Pass.

Answer

Exit All Files Properly.

Answer

Evaluate All Faults Promptly.

Question 3

When using the pack geometry manager, you want a widget to fill the available space in the parent container. Which argument for the 'fill' parameter should you use to make it expand in both horizontal and vertical directions?

Accepted Answer

fill=tk.BOTH. The 'BOTH' constant from the tkinter module is used with the fill parameter to expand in both dimensions.

Answer

fill='all'

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fill='both'

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fill=tk.EXPAND

Question 4

When documenting a complex function, which approach is most compliant with Google Style Python Docstrings regarding parameter types?

Accepted Answer

Use the 'Args:' section followed by the parameter name, type, and description.. Google Style requires explicit listing of types in the Args section to improve readability for static analysis tools.

Answer

Embed the types directly in the function name.

Answer

Include type hints in the docstring but omit them from the function signature.

Answer

Avoid documenting types to prevent redundancy with type hints.

Question 5

Which TWO of the following statements about the 'grid' geometry manager are correct?

Accepted Answer

It allows widgets to span across multiple rows or columns.. Grid allows for row/column spanning and absolute positioning within cells, but it is a row/column based system, not absolute XY.

Answer

It requires absolute pixel positioning.

Answer

It only supports a single column layout.

Answer

It cannot be mixed with the pack manager in the same parent.

Question 6

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. Requests.Session objects are not thread-safe in a way that prevents race conditions on connection pools. Each thread should ideally have its own session or a thread-safe connection pool mechanism.

Answer

Wrap the session object in a threading.Lock

Answer

Share a single global Session object across all threads

Answer

Disable connection pooling using 'pool_connections=0'

Question 7

When using the place() geometry manager, what is the purpose of 'relx' and 'rely'?

Accepted Answer

Relative position as a float from 0 to 1.. They represent the position of the widget as a fraction of the parent container's width and height (0.0 to 1.0).

Answer

Relative font size.

Answer

Relative pixel coordinates.

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Relative Z-index for layering.

Question 8

Which THREE of the following steps are required to initialize a TCP server socket?

Accepted Answer

Create a socket with socket.AF_INET and socket.SOCK_STREAM. A standard server lifecycle involves creating the socket, binding to an address/port, and listening for connections.

Answer

Call connect() to start the server

Answer

Call recv() before bind()

Question 9

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.

Answer

When the metaclass is first imported.

Answer

When the class itself is defined.

Question 10

What is the purpose of the 'weakref' module in relation to the Observer pattern?

Accepted Answer

To prevent memory leaks.. It allows the subject to maintain references to observers without preventing their collection by the garbage collector.

Answer

To allow private access to observers.

Answer

To ensure thread safety.

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To serialize observers.

Question 11

Why does the __init__ method not return anything?

Accepted Answer

Because it is designed to initialize an existing instance.. The __init__ method is for initialization only; the object creation is handled by __new__.

Answer

Because of internal Python constraints.

Answer

To allow for multiple initialization.

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Because it's a generator.

Question 12

When implementing secure coding practices in a web-facing Python application, how should you handle raw user input to prevent command injection?

Accepted Answer

Pass input arguments as a list to subprocess.run(args, shell=False).. Using the 'subprocess' module with 'shell=False' (the default) prevents the shell from interpreting user-provided strings as commands.

Answer

Pass the entire input string to os.system().

Answer

Concatenate the input string into a shell command for execution.

Answer

Sanitize input using a custom regex to remove special characters.

Question 13

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

Accepted Answer

Swallowing exceptions with an empty 'except' block.. Swallowing exceptions and catching BaseException are both poor practices.

Answer

Using 'finally' for cleanup.

Answer

Catching specific exceptions.

Answer

Raising custom exceptions.

Question 14

What is the result of applying the @staticmethod decorator to a method inside a class that also defines a metaclass?

Accepted Answer

The method is correctly bound as a static function regardless of the metaclass.. The @staticmethod decorator creates a static method object which is stored in the class dictionary; it is independent of the metaclass's __init__ logic for instance methods.

Answer

The metaclass must manually convert it back to a static method.

Answer

It raises a TypeError at class definition time.

Answer

The metaclass will treat the method as an instance method.

Question 15

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.

Answer

The child class will inherit the memory savings automatically.

Answer

The child class will be unable to add new attributes.

Question 16

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.

Answer

To improve method resolution speed.

Answer

To support multiple inheritance.

Question 17

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.

Question 18

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 19

You are implementing a custom context manager using a class. Which methods must be implemented to support the 'with' statement?

Accepted Answer

__enter__ and __exit__.. A context manager requires `__enter__` to set up the resource and `__exit__` to handle cleanup.

Answer

__setup__ and __teardown__.

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__open__ and __close__.

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__init__ and __del__.

Question 20

Which THREE features are associated with robust logging in production applications?

Accepted Answer

Log rotation to prevent disk space exhaustion.. Logging levels, rotation, and external log aggregation are standard.

Answer

Logging to 'stdout' exclusively.

Answer

Including personal user data in logs.