Examples of how to calculate the average (arithmetic mean) from a list of numbers in python:

Let's consider the following list

`l = [5, 3, 2, 9, 1, 4]`

to calculate the mean, there are several solutions:

Note: here the mean is based on the following estimator:

\begin{equation}

\hat{\mu} = \frac{1}{n} \sum x

\end{equation}

### Calculate the mean with the python module statistics

To calculate the mean from a list, a solution is to use the python module statistics, example:

`from statistics import mean`

`l_mean = mean(l)`

`print(l_mean)`

returns

`4.0`

### Calculate the mean with numpy

Another solution using numpy:

`import numpy as np`

`l_mean = np.mean(np.array(l))`

`print(l_mean)`

returns

`4.0`

### Calculate the mean with sum() et len()

`l_mean = sum(l) / len(l)`

`print(l_mean)`

returns

`4.0`

### Calculate the mean with a for loop

Another example using a for loop

`a = 0`

`b = 0`

`for i in l:`

`a += i`

`b += 1`

`l_mean = float(a) / b`

`print(l_mean)`

returns

`4.0`

### Create a function to calculate the mean

`def calculate_mean_from_list(list):`

`return sum(list) / len(list)`

`calculate_mean_from_list(l)`

returns

`4.0`

### Check that the list contains only numbers

Note: to be sure that the list contains only numbers a solution is to use the function isinstance(), illustration:

`l = [i for i in l if isinstance(i, (int, float))]`