PCPP1 Practice Test 6 — 10 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.

Answer

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.