```
Why does the order of numbers[i] += result and result +=numbers[i] matter?
What does += do?
What exactly is iterating?
What exactly is looping?
n = [3, 5, 7]
def total(numbers):
result = 0
for i in range(len(numbers)):
numbers[i] += result
return result
VS.
n = [3, 5, 7]
def total(numbers):
result = 0
for i in range(len(numbers)):
result += numbers[i]
return result
```

# 15 Iterating over a function

**klyhat**#1

Lets see your questions in order:

1) `numbers[i] += result`

is the same as `numbers[i] = numbers[i] + result`

If you switch the places of `numbers[i]`

and `result`

it will go into `result`

. (Because the original one goes into `numbers[i]`

)

2) Look at number 1

3) Iteration is a general term for taking each item of

something, one after another. Any time you use a loop, explicit or

implicit, to go over a group of items, that is iteration.

4) For loops are traditionally used when you have a piece of code which you want to repeat n number of times. As an alternative, there is the While Loop, however, while is used when a condition is to be met, or if you want a piece of code to repeat forever, for example -

*For loop from 0 to 2, therefore running 3 times.*

`for x in range(0, 3): print "We're on time %d" % (x)`

Hope this helps answer your questions!

**system**#3

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