Question 1 of 5
Which hook can customize isinstance(value, SomeClass)?
Look at the metaclass hook named for instance checks.
__instancecheck__() is the metaclass hook for customizing isinstance().
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Quick Check: Python Custom isinstance() and issubclass() Checks
Check your understanding of __instancecheck__(), __subclasscheck__(), metaclass lookup, and virtual relationships.
5 questions
~5 min
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Quick Check: Python Custom isinstance() and issubclass() Checks
Check your understanding of __instancecheck__(), __subclasscheck__(), metaclass lookup, and virtual relationships.
- Stuck? Each question has an optional hint.
- Skip a hard question and review it before your results.
- Questions and answer options can shuffle between attempts.
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Question 2 of 5
Which hook can customize issubclass(candidate, SomeClass)?
The hook name pairs with the built-in being customized.
__subclasscheck__() customizes the result of issubclass().
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Question 3 of 5
Where does Python look for these hooks when evaluating the built-in checks?
The second/first argument to these built-ins is itself a class.
Python looks for __instancecheck__() and __subclasscheck__() on that class's metaclass.
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Question 4 of 5
What does a custom instance/subclass check change?
Think about the distinction between a reported relationship and actual inheritance.
A custom check can report a virtual relationship without modifying __bases__ or __mro__.
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Question 5 of 5
Why might a custom __instancecheck__() call super().__instancecheck__()?
Delegation keeps the default answer available.
The metaclass can preserve normal isinstance behavior and add a second condition.
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Quiz results
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Which hook can customize isinstance(value, SomeClass)?Hint used
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Which hook can customize issubclass(candidate, SomeClass)?Hint used
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Where does Python look for these hooks when evaluating the built-in checks?Hint used
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What does a custom instance/subclass check change?Hint used
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Why might a custom __instancecheck__() call super().__instancecheck__()?Hint used