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Saturday, April 1, 2023

# How to Find the Sum of Elements in a List in Python

In Python, programmers work with a lot of lists. Sometimes, it is necessary to find out the sum of the elements of the lists for other operations within the program.

In this article, we will take a look at the following ways to calculate sum of all elements in a Python list:

## 1) Using sum() Method

Python provides an inbuilt function called sum() which sums up the numbers in a list.

### Syntax

Sum(iterable, start)
• Iterable â€“ It can be a list, a tuple or a dictionary. Items of the iterable have to be numbers.
• Start â€“ This number is added to the resultant sum of items. The default value is 0.

The method adds the start and the iterable elements from left to right.

Example:

sum(list)
sum(list, start)

Code Example:

# Python code to explain working on sum() method
# Declare list of numbers
numlist = [2,4,2,5,7,9,23,4,5]
numsum = sum(numlist)
print('Sum of List: ',numsum)
# Example with start
numsum = sum(numlist, 5)
print('Sum of List: ',numsum)

Output:

Sum of List:  61
Sum of List:  66

### Explanation

Here, you can see that the sum() method takes two parameters â€“ numlist, the iterable and 5 as the start value. The final value is 61 (without the start value) and 66 (with the start value 5 added to it).

## 2) Using for Loop

# Python code to calculate sum of integer list
# Using for loop
# Declare list of numbers
numlist = [2,4,2,5,7,9,23,4,5]
# Calculate sum of list
numsum=0
for i in numlist:
numsum+=i
print('Sum of List: ',numsum)

Output

Sum of List:  61

Explanation

Here, a for loop is run over the list called numlist. With each iteration, the elements of the list are added. The result is 61 which is printed using the print statement.

## 3) Sum of List Containing String Value

# Python code to calculate sum of list containing integer as string
# Using for loop
# Declare list of numbers as string
numlist = ['2','4','2','5','7','9','23','4','5']
# Calculate sum of list
numsum=0
for i in numlist:
numsum+=int(i)
print('Sum of List: ',numsum)

Output

Sum of List:  61

Here, the list called numlist contains integers as strings. Inside the for loop, these string elements are added together after converting them into integers, using the int() method.

## 4) Using While Loop

# Python code to calculate sum of list containing integer as string
# Using While loop
# Declare list of numbers as string
numlist = [2,4,2,5,7,9,23,4,5]
# Declare function to calculate sum of given list
def listsum(numlist):
total = 0
i = 0
while i < len(numlist):
total = total + numlist[i]
i = i + 1
# Call Function
# Print sum of list
totalsum = listsum(numlist);
print('Sum of List: ', totalsum)

### Explanation

In this program, elements of the numlist array are added using a while loop. The loop runs until the variable i is less than the length of the numlist array. The final summation is printed using the value assigned in the totalsum variable.

### Conclusion

Using a for loop or while loop is great for summing elements of a list. But the sum() method is faster when you are handling huge lists of elements.