Preforms simple linear regression in python

linear_regression.py

import warnings
#-----------------------------------------------------------------------------------------------------------------------
#power function
#python has one built in but the point of this program is to do unecessary things for practice
def power(x, pow):
    if type(pow) != int and pow > 0:
        warnings.warn("pow needs to be an integer value greater than 0")
    if pow == 0:
        return 1
    for i in range(pow-1):
        x = x*x
    return x
#-----------------------------------------------------------------------------------------------------------------------
#sum function
#python has one built in but the point of this program is to do unecessary things for practice
def ffsum(list):
    x = 0
    for i in list:
        try:
            x+= i
        except:
            warnings.warn("you probably don't have just numeric values in the list")
    return x
#-----------------------------------------------------------------------------------------------------------------------
#note here that x1, x2 denote the two lists that we will preform linear regression on
#we assume them to have the same size
def simple_linear_regression(x1, x2):
    if len(x1) != len(x2):
        warnings.warn("the lists are not the same size")
    x1x2 = []
    x1sq = []
    x2sq = []
    for i in range(len(x1)):
        x1x2.append(x1[i]*x2[i])
        x1sq.append(power(x1[i], 2))
        x2sq.append(power(x2[i], 2))
    #arbitrarily chose x1, could've used x2 as well
    n = len(x1)
    #Note we have to sloppily convert all of these values to float. Probably should find out a way to do it better.
    a = ((float(ffsum(x2))*float(ffsum(x1sq)))-(float(ffsum(x1))*float(ffsum(x1x2))))/(float(n)*float(ffsum(x1sq))-float(power(ffsum(x1), 2)))
    b = (float(n)*float(ffsum(x1x2))-float(ffsum(x1))*float(ffsum(x2)))/(float(n)*float(ffsum(x1sq))-float(power(ffsum(x1), 2)))
    print('a: ' + str(a))
    print('b: ' + str(b))
    return a, b
#-----------------------------------------------------------------------------------------------------------------------
if __name__ == "__main__":
    #test values
    x = [43,21,25,42,57,59]
    y= [99,65,79,75,87,81]
    #expected: a ~ 65.1416
    #expected: b ~ .385225
    simple_linear_regression(x, y)