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

Questions 1–5

1. 1application · medium

   A developer creates a subclass of dict that automatically converts all keys to strings. They override __setitem__ to store str(key). They also override __getitem__ to look up with str(key). When they use the .get() method with a non-string key, it returns None even though the key exists as a string. What is the cause?

   • AThe .get() method calls __getitem__, but the override only handles string keys, so non-string keys fail.
   • BThe .get() method works correctly, but the key was never stored because __setitem__ was also bypassed during initialization.
   • CThe .get() method is implemented in C and does not call the overridden __getitem__, so it looks up the raw key directly.
   • DThe .get() method uses a different internal hash table than __setitem__, so the key is stored in one table and looked up in another.
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2. 2foundation · easy

   When subclassing str to create a custom string type, which method would you override to change how the string is displayed when printed?

   • A__format__
   • B__repr__
   • C__len__
   • D__str__
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4. 3application · medium

   A developer needs a dictionary that automatically converts all values to strings when stored. They subclass dict and override __setitem__ to store str(value). They also override update() to normalize values. When they use the .setdefault() method with a non-string default, the stored value is not converted. Why?

   • AThe .setdefault() method is implemented in C and does not call __setitem__, so the value is stored as-is.
   • BThe .setdefault() method works correctly, but the developer must also override __getitem__ to convert values on retrieval.
   • CThe .setdefault() method raises an error because the default value is not a string.
   • DThe .setdefault() method calls __setitem__, but the override only works for subscript assignment, not for method calls.
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5. 4foundation · easy

   In a subclass of dict, how would you correctly call the parent's __init__ method to initialize the dictionary?

   • Aself.__init__(*args, **kwargs)
   • Bdict.__init__(self)
   • Csuper().__init__(*args, **kwargs)
   • Dsuper().__call__(*args, **kwargs)
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6. 5application · medium

   A developer needs a dictionary that automatically creates a default value when a missing key is accessed. They subclass dict and override __missing__. They test it with d['new_key'] and it works. However, when they use d.setdefault('new_key', 0), the default is not created. Why?

   • AThe setdefault() method works correctly, but the developer must also override __setitem__ to make the default persist.
   • BThe setdefault() method requires the default argument to be a callable, but 0 is not callable.
   • CThe setdefault() method is implemented in C and does not call __missing__, so the default is not triggered.
   • DThe setdefault() method calls __missing__, but the override only works for subscript access, not for method calls.
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