python - 生成列表元素产品的序列

Question

使用sympy，让我们说一个列表:

xs=[-2,-1,1,2]

我需要得到:

[(x-x_0),(x-x_0)*(x-x_1),(x-x_0)*(x-x_1)*(x-x_2),...(x-x_0)*(x-x_1)*(x-x_2)...*(x-x_n)]

对于我的列表 xs，这将是:

[(x+2),(x+2)*(x+1),(x+2)*(x+1)*(x-1),(x+2)*(x+1)*(x-1)*(x-2)]

我已经尝试过:

terminos = []
def lag_l(xx):
    x = Symbol("x")
    for x_i in xx:
        x__i = ((x-x_i) * prod(t) for t in terminos)
        terminos.append((x-x_i))
    print terminos[::-1]

所以:

lag_l([-2,-1,1,2])

但这只是打印相同的内容。我做错了什么？

Answer 1

def product_sequence(xs):
  x = Symbol('x')
  y = 1
  res = []
  for item in xs:
     y *= x - item
     res.append(y) 
  return res

或者，使用yield更优雅:

def product_gen(xs):
  x = Symbol('x')
  y = 1
  for item in xs:
     y *= x - item
     yield y

res = list(product_gen(xs))