What do the expressions mylist[::2] and mylist[::-1] represent?

The expression mylist[::2] represents slicing the list to obtain every second element, starting with the first element. This is because the slicing syntax mylist[start:stop:step] allows specifying a step value, and in this case, it is set to 2. Thus, it effectively skips every other element in the list.

On the other hand, mylist[::-1] is a common Python technique for reversing the list. The step value of -1 indicates that the slicing should be done in reverse order, starting from the end of the list and moving backward to the beginning. Therefore, this expression retrieves the elements in reverse arrangement.

Together, these two expressions illustrate the power of Python's list slicing capability, allowing for concise and efficient manipulation of list data structures.