This function, applied to an iterable

, returns the sum of its elements. There are two general
forms:
`S`

sum() sum(`S`

,`S`

)`I`

In the second form, the summing process starts with the
initial value

.
Examples:
`I`

>>> L=[1,2,3,4] >>> sum(L) 10 >>> sum(L,1000) 1010 >>> sum((), 1000) 1000