自定义余弦相似度函数

def cos_sim(data,usr1,usr2):
    fenzi=0
    for i in range(len(data[usr1])):
        a=data[usr1][i]*data[usr2][i]
        fenzi+=a
    fenmu1=0
    for i in data[usr2]:
        fenmu1+=i*i
    fenmu2=0
    for i in data[usr1]:
        fenmu2+=i*i
    from math import sqrt
    cos_s=fenzi/sqrt(fenmu1*fenmu2)
    return cos_s