# How to Calculate the Standard Deviation of a List in Python

You can use one of the following three methods to calculate the standard deviation of a list in Python:

Method 1: Use NumPy Library

```import numpy as np

#calculate standard deviation of list
np.std(my_list)
```

Method 2: Use statistics Library

```import statistics as stat

#calculate standard deviation of list
stat.stdev(my_list)```

Method 3: Use Custom Formula

```#calculate standard deviation of list
st.stdev(my_list)```

The following examples show how to use each of these methods in practice.

### Method 1: Calculate Standard Deviation Using NumPy Library

The following code shows how to calculate both the sample standard deviation and population standard deviation of a list using NumPy:

```import numpy as np

#define list
my_list = [3, 5, 5, 6, 7, 8, 13, 14, 14, 17, 18]

#calculate sample standard deviation of list
np.std(my_list, ddof=1)

5.310367218940701

#calculate population standard deviation of list
np.std(my_list)

5.063236478416116
```

Note that the population standard deviation will always be smaller than the sample standard deviation for a given dataset.

### Method 2: Calculate Standard Deviation Using statistics Library

The following code shows how to calculate both the sample standard deviation and population standard deviation of a list using the Python statistics library:

```import statistics as stat

#define list
my_list = [3, 5, 5, 6, 7, 8, 13, 14, 14, 17, 18]

#calculate sample standard deviation of list
stat.stdev(my_list)

5.310367218940701

#calculate population standard deviation of list
stat.pstdev(my_list)

5.063236478416116
```

### Method 3: Calculate Standard Deviation Using Custom Formula

The following code shows how to calculate both the sample standard deviation and population standard deviation of a list without importing any Python libraries:

```#define list
my_list = [3, 5, 5, 6, 7, 8, 13, 14, 14, 17, 18]

#calculate sample standard deviation of list
(sum((x-(sum(my_list) / len(my_list)))**2 for x in my_list) / (len(my_list)-1))**0.5

5.310367218940701

#calculate population standard deviation of list
(sum((x-(sum(my_list) / len(my_list)))**2 for x in my_list) / len(my_list))**0.5

5.063236478416116```

Notice that all three methods calculated the same values for the standard deviation of the list.