covariance.py

import math
import numpy as np

data_X = [5,6,8,12,15,18,10]
data_Y = [1,4,6,8,10,12,14]

def mean(x):
        return  sum(x)/len(x)

def de_mean(data):
# convert x by subtracting its mean ( so the result has mean 0)
        x_bar = mean(data)
        return [x_i - x_bar for x_i in data]

def covariance(x,y):
        n = len(x)
        return np.dot(de_mean(x), de_mean(y)) / (n-1)

print(covariance(data_X,data_Y))