Length and capacity … The capacity of a slice is the number of elements for which there is space allocated in the underlying array. At any time the following relationship holds: 0 <= len(s) <= cap(s) Recall that a slice is backed by a fixed-length array, which may have more elements than the slice. When this is the case, the capacity of the slice is said to be the current length of the slice, plus any unused elements in the backing array that extend beyond the final element of the slice.
