from math import sqrt

def multipl(a,b):

    sumofab=0.0

    for i in range(len(a)):

        temp=a[i]*b[i]

        sumofab+=temp

    return sumofab

def corrcoef(x,y):

    n=len(x)

    #求和

    sum1=sum(x)

    sum2=sum(y)

    #求乘积之和

    sumofxy=multipl(x,y)

    #求平方和

    sumofx2 = sum([pow(i,2) for i in x])

    sumofy2 = sum([pow(j,2) for j in y])

    num=sumofxy-(float(sum1)*float(sum2)/n)

    #计算皮尔逊相关系数

    den=sqrt((sumofx2-float(sum1**2)/n)*(sumofy2-float(sum2**2)/n))

    return num/den

x = [0,1,0,3]

y = [0,1,1,1]

print corrcoef(x,y) #0.471404520791