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sum() function in Python

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  • Difficulty Level : Easy
  • Last Updated : 18 May, 2022

Sum of numbers in the list is required everywhere. Python provides an inbuilt function sum() which sums up the numbers in the list.



sum(iterable, start)  
iterable : iterable can be anything list , tuples or dictionaries ,
 but most importantly it should be numbers.
start : this start is added to the sum of 
numbers in the iterable. 
If start is not given in the syntax , it is assumed to be 0.

Possible two syntaxes:

a is the list , it adds up all the numbers in the 
list a and takes start to be 0, so returning 
only the sum of the numbers in the list.
sum(a, start)
this returns the sum of the list + start 

Below is the Python implementation of the sum()

# Python code to demonstrate the working of 
# sum()
numbers = [1,2,3,4,5,1,4,5]
# start parameter is not provided
Sum = sum(numbers)
# start = 10
Sum = sum(numbers, 10)



Error and Exceptions

TypeError : This error is raised in the case when there is anything other then numbers in the list.

# Python code to demonstrate the exception of 
# sum()
arr = ["a"]
# start parameter is not provided
Sum = sum(arr)
# start = 10
Sum = sum(arr, 10)

Runtime Error :

Traceback (most recent call last):
  File "/home/", line 6, in 
    Sum = sum(arr)
TypeError: unsupported operand type(s) for +: 'int' and 'str'

So the list should contain numbers

Practical Application: Problems where we require sum to be calculated to do further operations such as finding out the average of numbers.

# Python code to demonstrate the practical application
# of sum()
numbers = [1,2,3,4,5,1,4,5]
# start = 10
Sum = sum(numbers)
average= Sum/len(numbers) 
print (average)



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