Trouble with Python sum function

[mr.me]

I don't know why we have to write a sum function for python when there already is one but
this is supposed to sum a list with varible values and I don't understand why it doesn't work, can someone help explain there error, I believe that I am not giving proper values to the line that adds but I don't realize why<

The Attempt at a Solution

def sum_list (a_list):
    length = len(a_list)
    counter = 0
    total= 0
    
    while(counter < length):
                              
        (a_list[counter] +total)          
    
        counter = counter + 1
    total = total + counter    
    return total      
#testing the functions
my_list = [3,3,3]print sum_list(my_list)

 

[Mark44]

I don't know why we have to write a sum function for python when there already is one but
this is supposed to sum a list with varible values and I don't understand why it doesn't work, can someone help explain there error, I believe that I am not giving proper values to the line that adds but I don't realize why<

The Attempt at a Solution

def sum_list (a_list):
    length = len(a_list)
    counter = 0
    total= 0
    
    while(counter < length):
                              
        (a_list[counter] +total) <<< Problem is here         
    
        counter = counter + 1
    total = total + counter    
    return total      



#testing the functions
my_list = [3,3,3]


print sum_list(my_list)

Your while loop isn't right. Python evaluates a_list[counter] + total for each element in the array, but you aren't storing the value anywhere.

You need something like this:
total = total + a_list[counter]

Then get rid of the line that says total = total + counter

 

[mr.me]

Thanks that's fixed.

To understand my mistake and clarify; is it fair to say that every time the loop ran it was adding 3 to zero then chucking that value into nothing as opposed to saving it, that's why the print was 3?

Again thankyou, I learn more here with a few of my mistakes and all your replies then my instructors teach.

 

[Mark44]

Thanks that's fixed.

To understand my mistake and clarify; is it fair to say that every time the loop ran it was adding 3 to zero then chucking that value into nothing as opposed to saving it, that's why the print was 3?

Yes, that's exactly what was happening.

Again thankyou, I learn more here with a few of my mistakes and all your replies then my instructors teach.

You're welcome! We enjoy being able to help out.

 

[LudusRex]

There are a few potential issues with the code provided. First, it is important to note that Python does indeed have a built-in sum function, so it is not necessary to create your own sum function. However, if you are trying to understand how the sum function works, it can be a useful exercise to try and create your own version.

In the code provided, there are a few areas that may be causing trouble. First, the line (a_list[counter] + total) does not actually assign the sum to a variable. It simply performs the calculation but does not store the result. To fix this, you could assign the sum to a variable, such as total, so that it can be used in the next iteration of the loop. Additionally, the line total = total + counter does not seem to be necessary and may be causing issues with the final sum.

A revised version of the code could look something like this:

def sum_list(a_list):
total = 0
for num in a_list:
total += num
return total

# testing the function
my_list = [3, 3, 3]
print(sum_list(my_list))

This code uses a for loop to iterate through each number in the list and add it to the total variable. It then returns the final sum. This approach is simpler and more efficient than using a while loop and a counter variable.

In conclusion, it is important to carefully consider the purpose and functionality of existing functions before attempting to create your own. Additionally, it is important to thoroughly test and debug your code to ensure it is functioning correctly.