The following methods can be defined to further emulate sequence objects. Immutable sequences methods should only define __getslice__(); mutable sequences, should define all three three methods.
self[i:j].
The returned object should be of the same type as self. Note
that missing i or j in the slice expression are replaced
by zero or sys.maxint, respectively. If negative indexes are
used in the slice, the length of the sequence is added to that index.
If the instance does not implement the __len__() method, an
AttributeError is raised.
No guarantee is made that indexes adjusted this way are not still
negative. Indexes which are greater than the length of the sequence
are not modified.
self[i:j].
Same notes for i and j as for __getslice__().
self[i:j].
Same notes for i and j as for __getslice__().
Notice that these methods are only invoked when a single slice with a single colon is used. For slice operations involving extended slice notation, __getitem__(), __setitem__() or__delitem__() is called.