Tim Peters wrote:
while we have N numbers, there are N+1 slice indices. So accumulate(xs) doesn't quite work. It needs to also have a 0 inserted as the first prefix sum (the empty prefix sum(xs[:0]).
Which is exactly what a this_is_the_initial_value=0 argument would do for us.
In this case, yes. But that still doesn't mean it makes sense to require the initial value to be passed *in* as part of the input sequence. Maybe the best idea is for the initial value to be a separate argument, but be returned as the first item in the list. I can think of another example where this would make sense. Suppose you have an initial bank balance and a list of transactions, and you want to produce a statement with a list of running balances. The initial balance and the list of transactions are coming from different places, so the most natural way to call it would be result = accumulate(transactions, initial = initial_balance) If the initial value is returned as item 0, then the result has the following properties: result[0] is the balance brought forward result[-1] is the current balance and this remains true in the corner case where there are no transactions. -- Greg