Index and slice

Every element of a list has a position, and positions count from 0: the first is values[0], the second values[1]. A minus counts from the end: values[-1] is the last.

1values = [10, 20, 30, 40, 50]
2values[1:4]   # [20, 30, 40]
3values[:2]    # [10, 20]
4values[3:]    # [40, 50]

A slice (a:b) gives a part of the list: a included, b not, just like range. An end left empty means "from the start" or "to the end".

A slice is not free: it builds a new list and copies every element in it. Take a slice inside a loop and that loop quietly becomes two nested loops.

Tasks