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
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