PCPP-32-101 1.8 Apply Subclassing of Built-In Classes PCPP-32-1 Practice Questions (Page 4)

Questions 16–20

1. 16application · medium

   A developer subclasses list to create a MaxList that tracks the maximum value. They override append() to update self.max_value and call super().append(). They also override __init__ to initialize max_value. When they use the .sort() method, the max_value becomes incorrect. Why?

   • AThe .sort() method works correctly, but the developer must override __setitem__ to update max_value during sorting.
   • BThe .sort() method calls append() for each element, which updates max_value incorrectly.
   • CThe .sort() method creates a new list and assigns it to the instance, losing the max_value attribute.
   • DThe .sort() method rearranges elements in place but does not update the max_value attribute, so it becomes stale.
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2. 17foundation · easy

   Which of the following correctly adds a class-level attribute to a subclass of a built-in class?

   • Aclass MyList(list): def __init__(self): self.max_size = 100
   • Bclass MyList(list): def __init__(self): max_size = 100
   • Cclass MyList(list): max_size = 100
   • Dclass MyList(list): self.max_size = 100
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4. 18application · medium

   A developer is building a configuration parser that must treat dictionary keys as case-insensitive. They create a class that inherits from dict and override __getitem__ and __setitem__ to normalize keys with .lower(). However, when they call the .update() method with another dictionary, the keys are stored with their original case. What is the most likely cause and the minimal fix?

   • AThe .update() method internally calls __setitem__ for each key, so the override should have worked; the issue is that the keys were already lowercased elsewhere.
   • BThe .update() method bypasses the overridden __setitem__; the developer must also override .update() to normalize keys and call super().update() with a normalized dictionary.
   • CThe .update() method works correctly, but the __getitem__ override is not being used because the keys are accessed via the internal C-level lookup.
   • DThe .update() method fails because the parent dict class cannot accept a subclass instance; the developer must convert the argument to a plain dict first.
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5. 19foundation · easy

   What is the effect of adding a new attribute in a subclass of a built-in class?

   • AThe attribute is automatically initialized to None for every instance
   • BThe attribute is added to the built-in class and available on all its instances
   • CThe attribute can only be accessed within the subclass's methods
   • DThe attribute is available on instances of the subclass but not on instances of the built-in class
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6. 20foundation · easy

   What is the primary purpose of subclassing a built-in class in Python?

   • ATo create a new class that inherits the built-in type's methods and can customize them
   • BTo access private attributes of the built-in type that are otherwise hidden
   • CTo replace the built-in type globally in the Python interpreter
   • DTo convert the built-in type into an abstract base class
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