In this article, we will be discussing the Python sum function and its application in

coding interviews. Python sum function is very helpful in coding interviews as it is easy to use and time-efficient. We’ll cover:

• What Is the Sum Function in Python?
• Sum Function Syntax
• Find Average Using Python Sum Function
• FAQs on Sum Function in Python

What Is the Sum Function in Python?

Sum function in Python is a built-in function that takes an iterable like a list, tuple, dictionary, or set as an argument, adds the elements of an iterable and returns the sum. We can also provide an optional start parameter which will be added to the sum of numbers in the iterable. 

By default, the value of the start parameter is zero. In Python 3.8, the start argument is a keyword argument that can be defined in the sum function call itself or elsewhere in the code.

Syntax

sum(iterable, start)

The start parameter is optional, and its default value is zero. Therefore we can use the Python sum function in two possible ways:

Let ‘a’ be the name of our iterable.

• Using the sum function as shown below will return the sum of the elements of a.

sum(a)                                               

• Using the sum functions shown below will return the sum of the elements of a + start.

sum(a, start)             

Example

Let us see some examples of how to use the Python sum function.

Using Python Sum Function on a List 

In the code below, we start with a list and use the Python sum function to calculate and print the sum of all the elements in our list.

a = [1, 2, 3, 5, 7, 11]

#using sum function without passing the start parameter

Sum = sum(a)
print(Sum)

#using sum function with start parameter

Sum = sum(a, 10)
print(Sum)

Output

29

39

Using Python Sum Function on a Tuple

In the code below, we will take a tuple and use the Python sum function to calculate and print the sum of all the elements in our tuple.

a = (3, 5 , 8, 13, 21)

#using sum function without the start parameter
Sum=sum(a)
print(Sum)

#using sum function with start parameter
Sum=sum(a, 11)
print(Sum)

Output

50

61

Using Python Sum Function on a Set 

In the code below, we will take a set and use the Python sum function to calculate and 

print the sum of all the elements in our set.

a = {1, 3, 5, 7, 9}

#using sum function without the start parameter
Sum=sum(a)
print(Sum)

#using sum function with start parameter
Sum=sum(a, 15)
print(Sum)

Output

25

40

Using Python Sum Function on a Dictionary 

In the code below, we will take a dictionary and use the Python sum function to calculate and print the sum of all the keys in our dictionary.

a={
    5: "Python",
  10: "sum",
  15: "function"
}

#using Python sum function without start parameter
Sum = sum(a)
print(Sum)

#using Python sum function with start parameter
Sum = sum(a, 20)
print(Sum)

Output

30

50

If, instead, you’d like to sum over all the values of a dictionary, then you'd need to explicitly pass them as .values() to the sum function as shown in the code below.

a={

   'a' : 10, 

   'b' : 12,

   'c' : 17

}

#using Python sum function without start parameter
Sum = sum(a.values())
print(Sum)

#using Python sum function with start parameter
Sum = sum(a.values(), 11)
print(Sum)

 Output

39

50

TypeError

You’ll get the TypeError when we use the Python sum function with an iterable consisting of data types other than numeric data types(int, float). Let’s see an example of TypeError in the Python sum function:

Example

a = ["interview", "kickstart", "Python", "sum"]

Sum = sum(a)
print(Sum)

Output

Traceback (most recent call last):

  File "file.py", line 2, in <module>

    print(sum(a))

TypeError: unsupported operand type(s) for +: 'int' and 'str'

Find Average using Python Sum Function

Let us solve a standard problem of finding the average using the Python sum function.

#find the average of numbers in the given list
a = [13, 47, 23, 55, 89]

Sum = sum(a)
Avg = Sum/len(a)

print(Avg)

Output

45

FAQs on Sum Function in Python

Question 1: Can we use the Python sum function to concatenate strings?

No, the Python sum function works only with numeric data types. To concatenate items of the given iterable (items must be strings), you may use the Python join() method.                     

Question 2: What will be the return value if we use the Python sum function with a dictionary?

If we use the Python sum function with a dictionary, the return value will be the sum of all the dictionary’s keys. Also, note that keys of the dictionary should be of a numeric data type; else, we will get TypeError.

Question 3: Can the Python sum function calculate the sum with exact precision?

No, if you need to add floating-point numbers with exact precision, then you should use math.fsum(iterable) instead.

import math

a = [1.1, 1.9, 2.1, 4.6]

# note that you cannot provide the start parameter when using fsum

Sum = math.fsum(a)
Avg = Sum/len(a)

print(Avg)

Output

2.425

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Article contributed by Anubhav Mishra