Iterating over a list in a function


Iterating over a list in a function

Oops, try again. total([0, 3, 6]) returned 0 instead of 9

It should have added three numbers instead of not adding them at all.

n = [3, 5, 7]

def total(numbers):
    result = 0
    for i in 1: range(len(numbers)):
        result = result + i 
        return result


Also, I am not fully sure about how to use and how the range function works, so I would be grateful if someone could explain more about that to me


The range function returns a list in Python 2, and in iterator in Python 3. We are concerned with Python 2.

my_range = range(5)

print my_range    # [0, 1, 2, 3, 4]

Notice the list does not contain the number 5? However, there are five elements in the list. The above usage with only one argument defaults to 0 as the starting value.

When a starting value is specified, then it takes the place of the default.

range(5) == range(0, 5)

Say we want a list of numbers from 1 to 10. It is a common assumption that it would be written like,

range(1, 10)

but that would be wrong since we know that the last value of the list will be 9 and not 10. To determine how many elements will be in the list, subtract the start value from the end value.

10 - 1 == 9

so the correct expression will then be,

range(1, 11)

# 11 - 1 == 10

# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Now because of the way range works it is great for iterating lists which are zero-indexed.

for i in range(len(numbers)):

i will be 0 to start, and will end at len(numbers) minus 1 which will be the correct final index of the list.


I had the same issue and finally figured it out. The indentation on the return line is the problem. Move it back in line with the "for.." line and it will work just fine.


Thanks so much for the advice!


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