Mastering Object-Oriented Python - Second Edition

Working with __getitem__(), __setitem__(), __delitem__(), and slices

The StatsList2 example didn't show us the implementation of __setitem__() or __delitem__() because they involve slices. We'll need to look at the implementation of a slice before we can implement these methods properly.

Sequences have two different kinds of indexes:

• a[i]. This is a simple integer index.
• a[i:j] or a[i:j:k]: These are slice expressions with start:stop:step values. Slice expressions can be quite complex, with seven different variations for different kinds of defaults.

This basic syntax works in three contexts:

• In an expression, relying on __getitem__() to get a value
• On the left-hand side of assignment, relying on __setitem__() to set a value
• On a del statement, ...