Quick Check: Python Special Methods and Object Behavior

Review

1. Which built-in function uses an object's __repr__() method?

   The repr() built-in asks the object for its official representation, which a class can customize with __repr__().
2. What must a normal __len__() implementation return?

   The __len__() hook supplies the result for len() and must return a non-negative integer.
3. Which operation can a class customize with __contains__()?

   __contains__() is the special method used for membership tests such as item in obj.
4. What does defining __eq__() primarily customize?

   __eq__() implements equality comparison, so it customizes == for instances of the class.
5. What should __add__() return when it does not support the other operand type?

   Returning NotImplemented tells Python that this implementation does not support the supplied operands, allowing the appropriate fallback behavior.
6. When an f-string contains a format specification after the colon, which special method customizes the formatted result for the object?

   Formatted string fields and format() call the type’s __format__ hook with the format specification. __str__ is the ordinary informal representation, and __repr__ is the debugging-oriented representation.
7. What type must a custom __bytes__() method return?

   __bytes__() supplies bytes(obj), so its return value must already be a bytes object. It does not return text or a mutable bytearray.