Array Slicing

Array slicing involves taking a subset from an array and allocating a new array with those elements.

In Python 2.7 you can create a new list of the elements in my_list, from start_index to end_index (exclusive), like this:

  my_list[start_index:end_index]

You can also get everything from start_index onwards by just omitting end_index:

  my_list[start_index:]

Careful: there's a hidden time and space cost here! It's tempting to think of slicing as just "getting elements," but in reality you are:

This takes $O(n)$ time and $O(n)$ space, where $n$ is the number of elements in the resulting list.

That's a bit easier to see when you save the result of the slice to a variable:

  tail_of_list = my_list[1:]Python 2.7

But a bit harder to see when you don't save the result of the slice to a variable:

  return my_list[1:]
# Whoops, I just spent O(n) time and space!

  for item in my_list[1:]:
    # Whoops, I just spent O(n) time and space!
    pass

Tanushree