problematic python function returns

Question

I have a function similar to the following:

def getCost(list):
  cost = 0
  for item in list:
    cost += item
  return cost

and I call it as so:

cost = getCost([1, 2, 3, 4])

This is GREATLY simplified but it illustrates what is going on. No matter what I do, cost always ends up == 0. If I change the value of cost in the function to say 12, then 12 is returned. If I debug and look at the value of cost prior to the return, cost == 10

It looks like it is always returning the defined number for cost, and completely disregarding any modifications to it. Can anyone tell me what would cause this?

Code works for me (note that you shouldn't name a variable list). — mechanical_meat
– mechanical_meat, Commented Oct 25, 2010 at 22:59
There's something missing. When I tried the sample, cost == 10 after the call. — outis
– outis, Commented Oct 25, 2010 at 23:00
I'm afraid you'll need to post more code... the method defined above (literally cut and paste into python 2.6 and 3.1 and got expected behavior) — cwallenpoole
– cwallenpoole, Commented Oct 25, 2010 at 23:01
Show code that you have run yourself and that demonstrates your problem. — John Machin
– John Machin, Commented Oct 26, 2010 at 2:17

Rafe Kettler · Accepted Answer · 2010-10-26 00:10:44Z

2

This should solve all of your problems (if summing the list items in cost is indeed what you're trying to do:

def getCost(costlist):
    return sum(costlist)

It accomplishes the exact same things and is guaranteed to work. It's also much more simple than using a loop and an accumulator.

answered Oct 26, 2010 at 0:10

Rafe Kettler

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4 Comments

Greg Hewgill Over a year ago

Or even simply: getCost = sum

Rafe Kettler Over a year ago

I just don't want to break all of his code that refers to getCost().

Greg Hewgill Over a year ago

You can assign functions like that in Python, and still call getCost() (it will then do exactly the same thing as sum()).

Rafe Kettler Over a year ago

Oh, I see. Learn something new about Python every day.

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