Quick Check: Python Custom Subscription and Container Behavior

Review

1. Which special method implements an expression such as catalog[1]?

   Define __getitem__() to implement instance subscription.
2. Which method handles scores[1] = 85?

   Assignment through brackets is handled by __setitem__().
3. When window[1:3] is evaluated, what reaches __getitem__()?

   A slice such as 1:3 is passed as a slice object.
4. Which hook does reversed(archive) use when the class defines it?

   __reversed__() supplies the custom reverse iterator.
5. Which mechanism is intentionally separate from this lesson for expressions such as list[int]?

   Class subscription can use __class_getitem__().
6. When a class subclasses collections.abc.Mapping, which methods must it implement?

   Mapping requires __getitem__(), __iter__(), and __len__(). Its mixin methods provide keys(), items(), values(), get(), membership testing, and equality. MutableMapping adds item assignment and deletion requirements.
7. A class inherits from collections.abc.Sequence. Which pair of methods must a concrete subclass implement?

   Sequence requires __getitem__() and __len__(). It provides operations such as count(), index(), iteration, membership, and reverse iteration. MutableSequence is the ABC for sequence types that also support mutation.
8. Which three methods must a concrete collections.abc.Set subclass implement?

   Set requires __contains__(), __iter__(), and __len__(). The ABC supplies comparisons and set-operation mixins such as intersection, union, difference, symmetric difference, and isdisjoint(). MutableSet additionally requires add() and discard().