错误是由于最后两行的缩进级别（如 j1-lee 的注解中所述）：

# ...
   sum += i*j

# deindentation
cosine_similarity = sum / ((sqrt(sums1)) * (sqrt(sums3)))
print (cosine_similarity)

这里是通过将 * 余弦相似性 * 的定义分解成更小运算的另一实现：

def scalar_product(a, b):
    return sum(a_i*b_i for a_i, b_i in zip(a, b))

def norm(a):
    return sum(a_i**2 for a_i in a )**.5

def cosine_similarity(a, b):
    return scalar_product(a, b) / (norm(a)*norm(b))

S1 = [1,0,0,0,1,0,0,2]
S3 = [0,1,1,2,0,1,2,0]

cs = cosine_similarity(S1, S3)
print(cs)
# 0.0   # orthogonality
cs = cosine_similarity(S1, S1)
print(cs)
# 1.0...# parallelity

我认为您只需要删除代码末尾的额外括号，如下所示：

cosine_similarity = sum / (sqrt(sums1)) * (sqrt(sums3))
print (cosine_similarity)