PCPP1 Practice Test 3 — 25 Questions

Question 1

You are implementing a Singleton pattern using the __new__ method. Why is it considered best practice to also define a __call__ method in the metaclass or use a decorator instead of just overriding __new__ in the base class?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

It prevents the creation of multiple instances during the unpickling process.. Overriding __new__ in a base class can lead to issues with pickling and deserialization, as __new__ is called every time an object is unpickled, potentially creating multiple instances.

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The __new__ method cannot accept variable arguments in Python 3.

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The __new__ method is reserved for static methods only.

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It is required for thread-safe access to the instance variable.

Question 2

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.

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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 3

Which practice is recommended when dealing with 'bare' except clauses in Python?

Accepted Answer

Always specify the exception type you intend to catch.. Bare 'except:' clauses catch SystemExit and KeyboardInterrupt, which can prevent the user from stopping a program.

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Use bare 'except:' for performance optimization.

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Use 'except Exception:' as the standard catch-all.

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Use 'except:' but log the error immediately.

Question 4

What is the primary difference between @classmethod and @staticmethod?

Accepted Answer

@classmethod receives the class as the first argument; @staticmethod does not.. @classmethod receives the class as the first argument, while @staticmethod receives no implicit class or instance argument.

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@staticmethod can access instance variables.

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@classmethod is for private methods.

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@classmethod is slower.

Question 5

How do you correctly call a method from a sibling class in a diamond inheritance structure using super()?

Accepted Answer

Use super() in each class to delegate to the next class in the MRO.. super() follows the Method Resolution Order (MRO), which correctly handles diamond inheritance by delegating calls to the next class in the chain, not just the parent.

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Call the grandparent class directly.

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Use the __bases__ attribute to iterate through parents.

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Explicitly call the sibling class method by name.

Question 6

Which magic method is responsible for providing the informal string representation of an object, typically used for user-facing output?

Accepted Answer

__str__. The __str__ method is used for informal, readable string representations, whereas __repr__ is for formal, unambiguous representations.

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__format__

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__unicode__

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__repr__

Question 7

When overriding the __getattr__ method, what must you be careful to avoid?

Accepted Answer

Infinite recursion by accessing non-existent attributes.. Infinite recursion occurs if you try to access an attribute inside __getattr__ that does not exist, triggering __getattr__ again.

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Raising AttributeError.

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Accessing class attributes.

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Calling super().__getattr__.

Question 8

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.

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To allow private methods.

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To improve method resolution speed.

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To support multiple inheritance.

Question 9

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.

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It triggers a SyntaxError.

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The class cannot be instantiated.

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The metaclass is ignored.

Question 10

Which TWO of the following are true about magic methods?

Accepted Answer

They provide hooks into Python language operators.. Magic methods start and end with double underscores, and they allow objects to integrate with Python's built-in syntax.

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They are only available for built-in types.

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They cannot be overridden.

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They are intended for direct calling by the user.

Question 11

What happens when you add two objects of a class that implements __add__?

Accepted Answer

The __add__ method is called.. The __add__ method is automatically called by the interpreter when the '+' operator is used.

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It does nothing.

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It concatenates the objects.

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It raises a TypeError.

Question 12

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.

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Store secrets in a private class attribute.

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

Question 13

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.

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__setup__ and __teardown__.

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__open__ and __close__.

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__init__ and __del__.

Question 14

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.

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Logging to 'stdout' exclusively.

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Including personal user data in logs.

Question 15

Why might you use the __init_subclass__ hook instead of a metaclass?

Accepted Answer

It is easier to implement and avoids metaclass conflicts.. __init_subclass__ provides a simpler way to perform logic when a subclass is created, without the complexity and inheritance issues associated with custom metaclasses.

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Metaclasses are deprecated.

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Metaclasses cannot be used for registration.

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It is faster at runtime.

Question 16

Which TWO of the following are correct regarding the 'with' statement in Python?

Accepted Answer

It requires the class to define __enter__ and __exit__.. The 'with' statement handles setup and teardown, and it requires both __enter__ and __exit__.

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It works by implicit __init__ calling.

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It only works with file objects.

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It can be used with any object.

Question 17

Which magic method enables index access (e.g., obj[i])?

Accepted Answer

__getitem__. The __getitem__ method allows an object to support indexing.

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__index__

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__setitem__

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__access__

Question 18

According to PEP 8, what is the maximum recommended length for a line of code?

Accepted Answer

79 characters.. PEP 8 suggests limiting lines to 79 characters to allow multiple files to be opened side-by-side.

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80 characters.

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No limit.

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120 characters.

Question 19

You need a color chooser dialog in your application. Which module contains this functionality?

Accepted Answer

tkinter.colorchooser. The 'tkinter.colorchooser' module provides the askcolor() function.

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tkinter.dialogs

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tkinter.colors

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tkinter.widgets

Question 20

You are building a Tkinter application and need to ensure that a Label widget expands to fill any extra horizontal space when the parent window is resized. Which configuration for the grid() layout manager achieves this?

Accepted Answer

parent.columnconfigure(0, weight=1) and widget.grid(sticky='ew'). The sticky parameter with 'ew' (east and west) ensures the widget stretches horizontally, while columnconfigure with weight > 0 allows the column to expand.

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widget.pack(fill='x', expand=True)

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widget.grid(sticky='nsew')

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widget.grid(padx=10, pady=10)