Python Program to find sum of array

Given an array of integers, find the sum of its elements.

Examples:

Input : arr[] = {1, 2, 3}
Output : 6
Explanation: 1 + 2 + 3 = 6

Input : arr[] = {15, 12, 13, 10}
Output : 50

Method 1: Iterating through the array and adding each element to the sum variable and finally displaying the sum.

Python3

# Python 3 code to find sum
# of elements in given array


def _sum(arr):

    # initialize a variable
    # to store the sum
    # while iterating through
    # the array later
    sum = 0

    # iterate through the array
    # and add each element to the sum variable
    # one at a time
    for i in arr:
        sum = sum + i

    return(sum)


# driver function
arr = []
# input values to list
arr = [12, 3, 4, 15]

# calculating length of array
n = len(arr)

ans = _sum(arr)

# display sum
print('Sum of the array is ', ans)

Output

Sum of the array is  34

Time complexity: O(n), 
Auxiliary Space: O(1)

Method 2: Using the built-in function sum(). Python provides an inbuilt function sum() which sums up the numbers in the list.

Syntax:

sum(iterable) 

iterable: iterable can be anything list, tuples or dictionaries, but most importantly it should be numbered.

Python3

# Python 3 code to find sum
# of elements in given array
# driver function
arr = []

# input values to list
arr = [12, 3, 4, 15]

# sum() is an inbuilt function in python that adds
# all the elements in list,set and tuples and returns
# the value
ans = sum(arr)

# display sum
print('Sum of the array is ', ans)

Output

Sum of the array is  34

Time complexity: O(n) 
Auxiliary Space: O(1)

Method 2: Using the reduce method. Array.reduce() method is used to iterate over the array and get the summarized result from all elements of array.

Syntax:

reduce( function, Array );

Python

from functools import reduce
# Python 3 code to find sum
# of elements in given array


def _sum(arr):

    # iterate over array
    # using reduce and get
    # sum on accumulator
    sum = reduce(lambda a, b: a+b, arr)

    return(sum)


# driver function
arr = []
# input values to list
arr = [12, 3, 4, 15]

# calculating length of array
n = len(arr)

ans = _sum(arr)

# display sum
print('Sum of the array is ', ans)

Output

('Sum of the array is ', 34)

Time complexity : O(n)
Auxiliary Space : O(1)

Example: Using enumerate function 

Python3

list1 = [12, 3, 4, 15];s=0
for i,a in enumerate(list1):
  s+=a
print(s)

Output

34

Time complexity: O(n)
Auxiliary Space: O(1)

Please refer complete article on Program to find sum of elements in a given array for more details!