slice

slice(stop)

slice(start, stop, [step])

• Standard indexing relies on slice(): a[start:stop:step] calls a.__getitem__(slice(start, stop, step)).
• slice() creates a shallow copy of the selected elements from the original list.
• Whenever you slice a list, the Python interpreter creates a new list and populates it with references to the elements you selected from the original list. Given that a reference needs 8 bytes on 64-bit systems, the overhead of copying references becomes noticeable when working with large lists. For example, slicing 1000 elements allocates almost 8kb worth of references.

islice(iterable, stop)

islice(iterable, start, stop, [step])

• Returns an iterator that produces the selected elements from the iterable. It skips start elements from the iterable, and then produces values until stop is reached, ...