PCPP-32-101 1.8 Apply Subclassing of Built-In Classes PCPP-32-1 Practice Questions (Page 5)

Questions 21–21

1. 21application · hard

   A developer subclasses int to create a Temperature class that stores a unit attribute. They write: class Temperature(int): def __new__(cls, value, unit='C'): obj = super().__new__(cls, value) obj.unit = unit return obj They create t = Temperature(25, 'C'). Later, they try to pickle t using the pickle module and get an error. What is the most likely cause?

   • AThe unit attribute is not picklable because it is a string, and pickle cannot serialize strings on int subclasses.
   • BThe custom __new__ signature requires an extra argument (unit), but pickle calls __new__ with only the value, causing a TypeError.
   • CThe int subclass is picklable by default, but the developer must call pickle.dumps(t, protocol=2) to support custom attributes.
   • DThe int subclass cannot be pickled because int is immutable and does not support __reduce__.
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