Obscure colon syntax for working with lists

>>> a = [1, 2, 3, 4, 5]

Slice list[start:end:step]

>>> a[1:]
[2, 3, 4, 5]

>>> a[1:-1]
[2, 3, 4]

>>> a[1:-1:2]
[2, 4]

Reverse

>>> a[::-1]
[5, 4, 3, 2, 1]

>>> a[:0:-1]
[5, 4, 3, 2]