How to get the average of a list in Python?

If we look at the official documentation, we can realize that Python does not come with a native mean() or average() function, as it does with sum() or len(). Therefore, calculating the average of a list in Python is not as easy as it may sound.

Let’s have a look at the options we have at our disposal to achieve this operation.

Use len() and sum() to calculate the average of a list

One of the easiest options is to use the sum() and len() functions. Indeed, the average of a list is equal to the sum of its elements divided by its length. Easy, right?

my_list = [1,2,3,4,5,6,7] avg = sum(my_list) / len(my_list) print(f'The average is {avg}.')
Code language: Python (python)

Output:

The average is 4.0.
Code language: CSS (css)

While this is the option I’d use in most cases, let’s explore other approaches.

Use a while loop to calculate the mean of a list

This approach is more naive and add complexity to the solution of our problem. That being said, if you are starting with Python, I’d try to avoid the built-in function as much as you can to understand the underlying logics they use.

my_list = [1,2,3,4,5,6,7] #variable to sum values sum_list = 0 #variable to count values n_elements = 0 #start a while loop while my_list: #add first element to our sum_list variable sum_list += my_list[0] #add 1 to our n_elements variable n_elements += 1 #remove first element of our list my_list = my_list[1:] #calculate average avg_list = sum_list/n_elements #print it print(avg_list)
Code language: Python (python)

Output:

4.0
Code language: Python (python)

Use reduce() to calculate the average of a list

Reduce() is a function from the functools library that allows us to apply a function cumulatively to the items of an iterable (a list in our case), from left to right, to reduce the iterable to a single value. Under the hood, it uses a simple code:

def reduce(function, iterable, initializer=None): it = iter(iterable) if initializer is None: value = next(it) else: value = initializer for element in it: value = function(value, element) return value
Code language: Python (python)

Applied to our example, we can use a lambda function to calculate the sum of our list and then divide it by its length.

from functools import reduce my_list = [1,2,3,4,5,6,7] sum_list = reduce(lambda a,b:a+b, my_list) avg_list = sum_list/len(my_list) print(avg_list)
Code language: Python (python)

Again, not as easy as our first option, but a good example of how you can use the reduce() function.

Use mean() from statistics to calculate the mean of a list

Even if Python doesn’t come directly with a mean function, you can import a function from the statistics library. It would save you creating a custom function.

from statistics import mean my_list = [1,2,3,4,5,6,7] avg_list = mean(my_list) print(avg_list)
Code language: Python (python)

Output:

4.0
Code language: Python (python)

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