How do I override the [] operator as in list[1:10]?

Question

How can I implement a customized list so that I can override the implementation of list[a:b]?

Thanks in advance!

Answer 1

Implement the __getitem__ hook; in case of a slice a slice object is passed in.

A simple version could be:

def __getitem__(self, index):
    if isinstance(index, slice):
        return [self[i] for i in range(*slice.indices(len(self)))]
    return self._internal_sequence[index]

Note that for slice assignment and slice deletion you must also implement the __setitem__ and __delitem__ hooks.

When overriding existing container types, you'll also have to handle the __getslice__ method; it is deprecated but Python 2 types still implement it. Again, there are corresponding __setslice__ and __delslice__ hooks for slice assignment and deletion too.

Answer 2

Define the __*item__() methods to customize indexing.