Author
Utkarsh Sahu
Director, Category Management @ Interview Kickstart || IIM Bangalore || NITW.
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:
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.
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.
sum(a)
sum(a, start)
Let us see some examples of how to use the Python sum function.
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)
29
39
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)
50
61
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)
25
40
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)
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)
39
50
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:
a = [“interview”, “kickstart”, “Python”, “sum”]
Sum = sum(a)
print(Sum)
Traceback (most recent call last):
  File “file.py”, line 2, in <module>
    print(sum(a))
TypeError: unsupported operand type(s) for +: ‘int’ and ‘str’
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)
45
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)
2.425
Whether you’re a Coding Engineer gunning for Software Developer or Software Engineer roles, or you’re targeting management positions at top companies, IK offers courses specifically designed for your needs to help you with your technical interview preparation!
If you’re looking for guidance and help with getting started, sign up for our free webinar. As pioneers in the field of technical interview prep, we have trained thousands of Software Engineers to crack the most challenging coding interviews and land jobs at their dream companies, such as Google, Facebook, Apple, Netflix, Amazon, and more!
————
Article contributed by Anubhav Mishra
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