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Python sum() Function

The sum() function sums of all the items of an iterable and returns the total.

If you specify an optional parameter start, it will be added to the final sum.

Syntax​

sum(iterable,start)

sum() Parameters​

Python sum() function parameters:

ParameterConditionDescription
iterableRequiredAn iterable (such as list, tuple, dictionary etc.)
startOptionalA value to be added to the final sum. Default value is 0.

sum() Return Value​

Python sum() function returns the sum of start and items of the given iterable.

danger

This function is created specifically for numeric values. For other values, it will raise TypeError.

Examples​

Example 1: Summing Numeric Elements of a List​

For example, you can sum numbers from a list:

numbers = [1,  2,  3,  4,  5]
result = sum(numbers)
print(result) # 15

output

15

Example 2: Providing an Initial start Value​

The start parameter of the sum() function allows you to specify an initial value for the summation. This can be especially useful when you want to start the sum from a non-zero value.

numbers = [1,  2,  3,  4,  5]
initial_value =  10
result = sum(numbers, initial_value)
print(result) # Output: 25

output

25

Example 3: Summing Strings (concatenating strings)​

You can not sum strings: the sum() function is primarily used for numeric values!

The join() method is the correct approach for combining strings in a list into a single string.

strings = ['Hello', ' ', 'World', '!']
result = ''.join(strings)
print(result) # Output: Hello World!

output

Hello World!

Example 4: Summing Elements of a Tuple​

This example sums the elements of a tuple containing floating-point numbers:

my_tuple = (10.99,  5.99,  8.49)
result = sum(my_tuple)
print(result) # Output: 25.47

output

25.47

Example 5: Summing Elements of a Tuple nested in a List with map() and sum()​

my_tuple = [(1,  3), (5,  6,  7), (2,  6)]
res = sum(map(sum, my_tuple))
print(res)  # Output:  30

output

30

Example 6: Summing Values of a Dictionary​

To sum the values of a dictionary, you can use the sum() function in combination with the .values() method of the dictionary, which returns an iterable of the dictionary's values.

prices_dict = {'apple':  1.2, 'banana':  0.5, 'orange':  0.8}
total_price = sum(prices_dict.values())
print(total_price)  # Output:  2.5

output

2.5

Example 7: Summing Floating-Point Numbers of a List​

The sum() function can add up the floating-point numbers in the list.

my_list = [10.2,  12.5,  11.8]
result = sum(my_list)
print(result) # Output: 34.5

output

34.5

Example 8: Summing Complex Numbers of a List​

The sum() function is used to add complex numbers from a list, resulting in a complex number.

my_list = [3 +  2j,  5 +  6j]
result = sum(my_list)
print(result) # Output: (8+8j)

output

(8+8j)

Example 9: Summing Decimal Numbers of a List​

This example shows summing Decimal numbers from a list using sum() function:

from decimal import Decimal

my_list = [Decimal("10.2"), Decimal("12.5"), Decimal("11.8")]
result = sum(my_list)
print(result) # Output: Decimal('34.5')

output

34.5

Example 10: Summing Fraction Numbers of a List​

The sum() function adds Fraction numbers from a list, returning a simplified Fraction as the result.

from fractions import Fraction

my_list = [Fraction(51,  5), Fraction(25,  2), Fraction(59,  5)]
result = sum(my_list)
print(result) # Output: 69/2

output

69/2

Example 11: Concatenating Lists using sum() function​

This example shows how sum() function can be used to concatenate lists, effectively flattening a list of lists. The second argument to sum() is an empty list, which serves as the starting value for the summation.

my_list = [[1,  2,  3], [4,  5,  6]]
result = sum(my_list, [])
print(result) # Output: [1,  2,  3,  4,  5,  6]

output

[1, 2, 3, 4, 5, 6]

Example 12: Concatenating Tuples using sum() function​

This example shows how sum() function can concatenate tuples by providing an empty tuple as the starting value. The result contains the flattening of the nested tuples given as input.

my_tuple = ((1,  2,  3), (4,  5,  6))
result = sum(my_tuple, ())
print(result) # Output: (1, 2, 3, 4, 5, 6)

output

(1, 2, 3, 4, 5, 6)

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