List comprehension for running total

Question

I want to get a running total from a list of numbers.

For demo purposes, I start with a sequential list of numbers using range

a = range         


        

Answer 1

I'm not sure about 'elegant', but I think the following is much simpler and more intuitive (at the cost of an extra variable):

a = range(20)

runningTotal = []

total = 0
for n in a:
  total += n
  runningTotal.append(total)

The functional way to do the same thing is:

a = range(20)
runningTotal = reduce(lambda x, y: x+[x[-1]+y], a, [0])[1:]

...but that's much less readable/maintainable, etc.

@Omnifarous suggests this should be improved to:

a = range(20)
runningTotal = reduce(lambda l, v: (l.append(l[-1] + v) or l), a, [0])

...but I still find that less immediately comprehensible than my initial suggestion.

Remember the words of Kernighan: "Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it."