Syntax

• a[start:end] # items start through end-1
• a[start:] # items start through the rest of the array
• a[:end] # items from the beginning through end-1
• a[start:end:step] # start through not past end, by step
• a[:] # a copy of the whole array
• source

Remarks

• lst[::-1] gives you a reversed copy of the list
• start or end may be a negative number, which means it counts from the end of the array instead of the beginning. So:

a[-1]    # last item in the array
a[-2:]   # last two items in the array
a[:-2]   # everything except the last two items

(source)