python - Summing elements in a list

79
votes

Here is my code, I need to sum an undefined number of elements in the list. How to do this?

l = raw_input()
l = l.split(' ')
l.pop(0)

My input: 3 5 4 9 After input I delete first element via l.pop(0). After .split(' ') my list is ['5', '4', '9'] and I need to sum all elements in this list.

In this case the sum is 18. Please notice that number of elements is not defined.

7
pythonlistsum
@JakobBowyer I need to delete first entry – treng
@AshwiniChaudhary isn't that obvious? is a string... he used raw_input() – KurzedMetal
Does this answer your question? Sum a list of numbers in Python – AMC

7 Answers

177
votes

You can sum numbers in a list simply with the sum() built-in:

sum(your_list)

It will sum as many number items as you have. Example:

my_list = range(10, 17)
my_list
[10, 11, 12, 13, 14, 15, 16]

sum(my_list)
91

For your specific case:

For your data convert the numbers into int first and then sum the numbers:

data = ['5', '4', '9']

sum(int(i) for i in data)
18

This will work for undefined number of elements in your list (as long as they are "numbers")

Thanks for @senderle's comment re conversion in case the data is in string format.

8
votes
>>> l = raw_input()
1 2 3 4 5 6 7 8 9 10
>>> l = l.split()
>>> l.pop(0)
'1'
>>> sum(map(int, l)) #or simply sum(int(x) for x in l) , you've to convert the elements to integer first, before applying sum()
54
6
votes

Python iterable can be summed like so - [sum(range(10)[1:])] . This sums all elements from the list except the first element.

>>> atuple = (1,2,3,4,5)
>>> sum(atuple)
15
>>> alist = [1,2,3,4,5]
>>> sum(alist)
15
5
votes

You can also use reduce method:

>>> myList = [3, 5, 4, 9]
>>> myTotal = reduce(lambda x,y: x+y, myList)
>>> myTotal
21

Furthermore, you can modify the lambda function to do other operations on your list.

2
votes

You can use sum to sum the elements of a list, however if your list is coming from raw_input, you probably want to convert the items to int or float first:

l = raw_input().split(' ')
sum(map(int, l))
1
votes

You can use map function and pythons inbuilt sum() function. It simplifies the solution. And reduces the complexity.
a=map(int,raw_input().split())
sum(a)
Done!

0
votes
def sumoflist(l):    
    total = 0    
    for i in l:
        total +=i
    return total