Python sum()
The sum() is a built-in python function which sums all the items of a given iterable.
The Python sum() function is a built-in function that computes the total of all numeric items in an iterable. It accepts two parameters: iterable (a sequence of numbers such as a list, tuple, or set) and an optional start value that is added to the total (defaulting to 0). The function returns the sum of start plus all the numbers in the iterable. It works with integers, floats, and any objects that support the addition operator, but it explicitly does not support strings (use str.join() instead). The sum() function is essential for financial calculations, statistical computations, and data aggregation tasks. A real-world example is calculating the total price of items in a shopping cart or computing the average of a list of scores by dividing sum(scores) by len(). It pairs well with list comprehensions and generator expressions for filtered summation.
What does sum() return?
The sum() function returns the arithmetic total of all items in the iterable plus the start value. The return type matches the type of the elements being summed (integer, float, etc.).
When should you use sum()?
Use sum() when you need to compute the total of a collection of numbers, such as adding up prices, scores, measurements, or any other numeric data stored in a list, tuple, or generator.
The syntax of the sum() function is:
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sum(iterable, start)
sum() Parameters
The sum() functions takes two parameters as argument:
- iterable - Any iterable or sequence which contains numbers. For Example list, tuple, dict, etc)
- start (Optional) - A value that is added to the return value. Default it will take 0.
Let see some examples of sum() in python.
Example 1: How to use sum() with python list?
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numbers = [2,8,4,3,7,1]
# start parameter is not provided
numbers_sum = sum(numbers)
print(numbers_sum)
# start = 10
numbers_sum = sum(numbers, 10)
print(numbers_sum)
Output:
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25
35
Example 2: Using floating numbers with sum() function.
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numbers = [4.6,6.2,0.4,5.3]
# start parameter is not provided
numbers_sum = sum(numbers)
print(numbers_sum)
Output:
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16.5
Example 3 : Using negative numbers with sum() functions.
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numbers = [-2,-9,-4,-3,-5]
# start parameter is not provided
numbers_sum = sum(numbers)
print(numbers_sum)
Output:
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-23
Common Use Cases
A common use case for sum() is totaling a list of prices in an e-commerce application, such as sum(item['price'] for item in cart). Another practical scenario is computing running totals or aggregates in data analysis, such as summing monthly revenue figures or sensor readings. It is also frequently combined with len() to calculate averages, or used with the start parameter to add a base value like a shipping fee to a subtotal.
Rules of sum()
- sum() function takes on iterable as parameters.
- All the iterable must contain numbers as all items.
Machine Learning Engineer at Codiste, specializing in Generative AI, NLP, and Computer Vision. Building production AI systems with Python.