# Python program to find standard deviation

Standard deviation in Python: Here, we are going to learn how to find the standard deviation using python program?
Submitted by Anuj Singh, on June 30, 2019

While dealing with a large data, how many samples do we need to look at before we can have justified confidence in our answer? This depends on the variance of the dataset.

Variance tells us about the divergence and the inconsistency of the sample. The standard deviation of a collection of values is the square root of the variance. While it contains the same information as the variance. But Standard deviation is quite more referred. Why? Look at the below statement:

The mean income of the population is 846000 with a standard deviation of 4000.
The mean income of the population is 846000 with a variance of 16000000.

Now see which statement is more favorable and therefore we use standard deviation.

So in this python article, we are going to build a function for finding the SD.

So the following function can be used while working on a program with big data which is very useful and help you a lot.

So here is the function code:

```def stdv(X):
mean = sum(X)/len(X)
tot = 0.0
for x in X:
tot = tot + (x - mean)**2
return (tot/len(X))**0.5

# main code
#  a simple data-set
sample = [1, 2, 3, 4, 5]
print("Standard Deviation of the sample is: ", stdv(sample))

sample = [1, 2, 3, -4, -5]
print("Standard Deviation of the sample is: ", stdv(sample))

sample = [10, -20, 30, -40, 50]
print("Standard Deviation of the sample is: ", stdv(sample))
```

Output:

```Standard Deviation of the sample is:  1.4142135623730951
Standard Deviation of the sample is:  3.2619012860600183
Standard Deviation of the sample is:  32.61901286060018
```

Preparation