slice([start,] stop[, step])
Returns a slice object representing the set of indices specified
by range(start, stop, step). The start and step
arguments default to None.
Slice objects have read-only data attributes start, stop and step
which merely return the argument values (or their default). They
have no other explicit functionality; however they are used by
Numerical Python and other third party extensions. Slice objects
are also generated when extended indexing syntax is used. For
example: a[start:stop:step] or a[start:stop,
i].