The Python *math.fsum()* function takes a list of floating point numbers, and sums them up (totals/adds them all together). Here’s how to use it, with examples.

## Summing/Totalling/Adding Numbers

The concept of summing numbers is simple – take the numbers you wish to get the total of, and add them all together.

1 + 2 + 3 = 6

It’s basic arithmetic that you’ll use daily when writing computer software in any language.

## Summing Numbers in Python

The *sum()* function in Python sums numbers. It’s a built-in function, which can be used anywhere in your code without having to import any dependencies.

**BUT**

You should **NOT** use it to sum floating point numbers when high accuracy is required.

## Floating Point Precision Errors When Using *sum()*

Otherwise, you are likely to run into floating point precision errors:

sum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1]) # results in 0.9999999999999999

Above, an inaccurate result is returned by the *sum()* function – the answer should be **1**, not **0.9999999999999999**. *math.fsum()* will give the correct result:

import math math.fsum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1]) # results in 1.0

*math.fsum()* Syntax

The syntax for the *math.fsum()* function is as follows:

import math math.fsum(ITERABLE)

Note that:

**ITERABLE**can be any Python iterable, containing numerical values- Usually, this is a list of numbers

- Note that the
*math*library must be imported into your Python script before*math.fsum()*can be called

*math.fsum()* Example

Below, a list of floating point numbers is summed:

import math numberList = [2.1, 6.43, 18.3, 3.0] numberSum = math.fsum(numberList)