Question

I have a function which looks like that:

  def roulette(self):
    sum = 0
    lst = []
    for x in self.drinkList:
        sum += x.fitness
        lst.append(sum)
    return lst

Can it be replaced with list comprehension expression or something more efficient than for loop?

PS: it apperars that if I do random.randrange(0), it raises an exception ValueError: empty range for randrange(). Is there a way to avoid it without using if test?

Answer 1

It’s actually possible to ‘peek’ at the list being built in a list comprehension. the outermost list has the name _[1], which of course is not a valid python identifier, so it must be accessed in another way:

def roulette(self):
    return [drink.fitness + (locals()['_[1]'][-1] if locals()['_[1]'] else 0) 
            for drink 
            in self.drinkList]

But just because you can doesn’t mean you should; go with your for loop, it looks like exactly what it does, and also doesn’t rely on an undocumented python feature.